Download TOPIC OUTLINE I. Introduction A. Renal Function B. The Nephron II

OS 213 [A]: Digestion and Excretion
1
Lec 02: Renal Function Tests
March 3, 2014
Lynn C. Almazan-Gomez, MD
TOPIC OUTLINE
I.
II.
III.
IV.
V.
VI.
VII.
Introduction
A. Renal Function
B. The Nephron
Glomerular Filtration Rate
A. Filtration
B. 24-Hour Urine Measurement Modalities of GFR
C. Alternatives to the 24-Hour Urine Modalities
Renal Function Tests
A. Cystatin C
B. Review of Lipid Metabolism
C. New Tubular Biomarkers
Urinalysis
A. Physical Characteristics
B. Chemical Characteristics
C. Urine Protein: Urine Creatinine Ratio
Urine Microscopy
A. Specimen Collection
B. Urine Sediments
C. Hematuria
D. Urine Volume
E. Bilirubin
F. Urobilinogen
G. Ketones
H. Nitrite
Imaging
A. Plain KUB X-Ray
B. Intravenous Pyelogram
C. Excretion Urography
D. Antegrade Pyelography
E. Retrograde Pyelography
F. Micturating Cystouretography
G. Cytoscopy
H. Ultrasonography
I. Computed Tomography (CT Scan)
J. Magnetic Resonance Imaging (MRI)
K. Arteriography or Venography
L. Radionucleide Studies
M. Renal Scintigraphy
Summary
Legends:
From the Powerpoint presentation
From the lecturer
T/N: Wala sa UVLE file na nakaupload iyong algorithm, at hindi naman siya
diniscuss masyado ni Ma’am. Ihahabol na lang naming iyong appendices, kasi
medyo malabo
I. INTRODUCTION
OVERVIEW OF RENAL STRUCTURE
Kidney
(Urine Production)
↓
Ureters
(Transport to the Bladder)
↓
Urinary Bladder
(Urine Storage)
↓
Urethra
(Transport to the Exterior)
OVERVIEW OF RENAL FUNCTION
 Homeostatic Regulation
o Maintenance of proper plasma volume and concentration
 Excretion and Elimination
o Removal of organic wastes from body fluids
 Endocrine Function
o Production of hormones such as renin, erythropoietin, and
vitamin D3
OVERVIEW OF RENAL EVALUATION MODALITIES
 Glomerular Filtration Rate (GFR)
 Urinalysis
 Imaging
NOTE: These modalities are only used for steady state evaluations!
A. RENAL FUNCTION
HOMEOSTATIC REGULATION
 Regulation of blood volume and pressure
o Urine volume is adjusted in order to maximize or minimize water
loss
o Regulatory hormones such as renin and erythropoietin are
produced and released by the kidneys
 Regulation of plasma ion concentration
o Achieved through controlled K+, Na+, and Cl- excretion in urine
o Vitamin D3 is a major regulatory hormone for calcium ion levels
in the blood
 Regulation of blood pH
o Achieved through controlled hydrogen ion (H+) and bicarbonate
(HCO3-) excretion in urine
 Nutrient Conservation
o Achieved by preventing the urinary excretion of vital substances.
o At the Proximal Convoluted Tubule (PCT), all glucose, amino
acids, K+, HCO3-, and 75% of Na+ is reabsorbed isotonically by
energy-dependent mechanisms
 Metabolism of Toxic Substances
o Antibiotics, antifungals, etc.
EXCRETION AND ELIMINATION
 The mechanism for excretion of excess electrolyte, nitrogenous
wastes, and organic acids are similar
 Maximal Excretory Rate
o Dependent on the plasma concentration of the solute, as well
as its glomerular filtration rate
o Does not exceed the amount of fluid transferred through the
glomeruli by ultrafiltration
 Maximal Excretory Amount
o Amount extracted through ultrafiltration at the glomerulus +
Amount secreted by tubular cells
 The primary objective in evaluation of renal excretory function is to
detect quantitatively the normal capacities, or the improvement of
impaired ones.
o Kidneys have a 60% functional reserve
o Dialysis is indicated for functional reserves amounting to 5%
ENDOCRINE FUNCTION
 Kidneys have primary endocrine function since they produce
hormones
 In addition, the kidneys serve as sites of degradation for hormones
such as insulin and aldosterone
 Hormones produced in the Kidneys:
o Erythropoietin
 Produced in the peritubular capillaries of the renal cortex
 Secreted in response to low oxygen levels in the blood
 Acts on bone marrow, eliciting an increase in red blood cell
production
o Renin
 Produced by cells of the juxtaglomerular apparatus
 Secreted in response to hyponatremia, a decrease in renal
perfusion, or changes in angiotensin II and antidiuretic
hormone (ADH) levels
 Key stimulus for aldosterone release from the zona
glomerulosa of the adrenal cortex
o Vitamin D3
 A.k.a. Calcitriol, 1,25-dihydroxycholecalciferol
 Converted from 25-hydroxycholecalciferol at the proximal
convoluted tubule
 Promotes GIT absorption of calcium  calcium-phosphorus
balance
B. THE NEPHRON
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VOLUME CONSIDERATIONS
 Receives 25% of resting cardiac output at any given time
 Glomerular Filtration
o 120mL per minute
o 170L in a day
 Urine Output
o 1-2L per day
Fun facts from 2016 [A]:

Shen Franz Jerry
Functional unit of the kidney
Each kidney contains 1,000,000 to 1,300,000 nephrons
Components:
o Glomerulus (ultrafiltration)
o Renal Tubules (secretion, reabsorption)
The body contains around 5L of blood
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Lec 02: Renal Function Tests
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99% of renal blood flow is reabsorbed
Quantity of blood filtered in a day: 200L
Quantity of urine per act of urination: 200cc
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OS 213
The Net Filtration Pressure is the sum total of these four vectors.
Any change in the forces, as in disease processes, will affect the
GFR.
THE SCHEMATIC NEPHRON
AUTOREGULATION OF FILTRATION
 Autoregulation of glomerular filtration rate takes place over a wide
range of blood pressures (Mean Arterial Blood Pressure =
80mmHg to 180mmHg)
o Mean Arterial Pressure (MAP) = (Systolic BP + Diastolic BP +
Diastolic BP) / 3
II. GLOMERULAR FILTRATION RATE
A. FILTRATION
THE RENAL CORPUSCLE
 Layers of the golmerular f iltration membrane:
o Glomerular Endothelium
 Fenestrated by endothelial pores
o Glomerular Basement Membrane
 Membranous Glomerulonephritis: thickening of the
basement membrane
o Podocyte Layer
 Made up of the foot processes (pedicels) of podocytes, as
well as the slit processes in between these pedicels
 Podocytes exhibit cross-talk through integrin and nephrin
molecules
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Autoregulation is primarily achieved through the actions of the
Renin-Angiotensin-Aldosterone System (RAAS) on the afferent
and efferent arterioles of the kidney.
Controlled vasodilations and vasoconstrictions of the
aforementioned arterioles compensate for changes involving the
perfusion of the nephrons
Figure 1. Layers of the Glomerular Filtration Membrane
PHYSIOLOGY OF FILTRATION
 Filtration is a force-driven process
o Forces that promote flow towards the Bowman’s Capsule:
 Hydrostatic Pressure exerted by blood in the glomerulus
 Colloid Osmotic Pressure exerted by non-diffusing solutes
in the Bowman’s Capsule not present in the glomerulus
o Forces that promote flow towards the glomerulus
 Hydrostatic Pressure exerted by fluid in the Bowman’s
Capsule
 Colloid Osmotic Pressure exerted by non-diffusing solutes
in the glomerulus not present in the Bow man’s Capsule
Shen Franz Jerry
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Lec 02: Renal Function Tests
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 Constricts in hypertension
 Dilates in hypotension and hypovolemia
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OS 213
An ideal chemical marker should be:
o Be freely filtered at the gloveruli
o Not to be bound to plasma proteins
o Not be metabolized
o Be non-toxic
o Be excreted only by the kidneys
o Be neither reabsorbed nor secreted by the renal tubules
o Be stable in blood and urine
o Be easily measured
1. INULIN
Gold standard for measuring GFR
Freely filtered by the glomerulus
Neither reabsorbed nor secreted by the renal tubules
Clinically Impractical
o Scarce
o Expensive
o Requires hospital admission
Common source of error: Incomplete Urine Collection
Inulin Clearance is used to determine the GFR
GFR = [Urine Concentration of Inulin] x [Volume of Urine]
[Plasma Concentration of Inulin]
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GLOMERULAR FILTRATION RATE
 Volume of plasma filtered per unit time
o Approximate value: 180L per day
o Urine output: 1-2L per day
 Implication: 99% of filtrate is reabsorbed
 Influenced by:
o Blood pressure and flow
o Obstruction of urine outflow
 ↑ Hydrostatic Pressure in Bow man’s Capsule
 ↓ GFR
o Loss of protein-free fluid
 Leads to changes in osmotic pressure
o Hormonal Regulation
 Renin-Angiotensin
 Aldosterone
 Antidiuretic Hormone (ADH): produced in the hypothalamus,
and stored at the neurohypophysis
 Atrial Natriuretic Peptide (ANP): produced in the atria of the
heart
JUXTAGLOMERULAR APPARATUS (JGA)
 Composed of Juxtaglomerular and Macula Densa Cells
o Juxtaglomerular Cells are located near the wall of the afferent
arteriole
o Macula Densa Cells are situated around the final portion of the
Loop of Henle
 Function
o Controls glomerular perfusion and f iltration
 Mechanism of Action
o Macula Densa Cells monitor changes in Na+, Cl-, and water
balance present in the Loop of Henle
o The JGA w ill then respond to these changes through the actions
of the RAAS, which is initiated by renin-producing
juxtaglomerular cells
o Controlled vasodilations and vasoconstrictions of the
afferent and efferent arterioles then ensue, leading to the
autoregulation of the GFR
2. IOHEXOL
Radiopharmaceutical
Freely filtered by the glomerulus
Neither reabsorbed nor secreted by the renal tubules
Administration: IV Bolus
Not widely used yet
3. CREATININE
End product of creatine metabolism
98% of body creatine is found in the muscles, serving as highenergy compounds in the form of creatine phosphate
1-2% of total muscle creatine is converted daily to creatinine through
the spontaneous, non-enzymatic loss of water or phosphate
Characteristics:
o Freely filtered by the glomerulus
o Secreted by the renal tubules (~10% of creatinine in urine)
o Not reabsorbed by the renal tubules
o Plasma creatinine is an endogenous substance not affected by
diet
o Levels of creatinine clearance remain fairly constant in adult life
GFR = [Urine Concentration of Creatinine] x [Volume of Urine] /1440 minutes]
[Plasma Concentration of Creatinine]
=
[Creatinine Clearance]
[Plasma Concentration of Creatinine]
.
UNIT: mL/minute
SERUM CREATININE
 From the above equation, it can be noted that plasma/serum
creatinine has an inverse relationship with the GFR
o Implication: Plasma/Serum creatinine may be used to
evaluate kidney function
o ↑ Plasma/Serum Creatinine: ↓ GFR, ↓ Kidney Function
B. 24-HOUR URINE MEASUREMENT MODALITIES OF GFR

The following measurement modalities are meant to assess
glomerular filtration rates in the steady state
o Implication: These modalities can only be used to assess
normal and chronically diseased kidneys.
o Acute disease states require alternative assessment modalities
Shen Franz Jerry
Figure 5. Serum Creatinine vs. GFR. Take note that serum creatinine
values may not be too sensitive to renal function (50% decline in GFR
before an increase in serum creatinine may be seen)
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Lec 02: Renal Function Tests
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Normal Plasma/Serum Creatinine values: 0.6 to 1.2 mg/dL
Factors that affect serum creatinine:
o Increased Creatinine Production
 Rhabdomyolysis
 Meat
o Decreased Creatinine Excretion
 Cimetidine (Cimetidine Challenge Test) – used to negate the
effects of transplantation
 Triamterene
 Probenecid
 Amiloride
 Trimethoprim
 Spironolactone
o Measured Bias
 Not caused by an actual increase in creatinine
 Endogenous: Ketones, Ketoacids, Glucose, Bilirubin, Urate,
Urea, Fatty Acids
 Exogenous: Cephalosporins, 5-FU, Phenylacetyl Urea
OS 213
GFR = [140 – age in years] x [lean body weight in kg] x 0.85*
72 x [Serum Creatinine]
MODIFICATION OF DIET IN RENAL DISEASE STUDY (MDRD)
 Designed to assess the effect of dietary restriction and BP
Control on progression of renal disease
 Data from the study helped develop an equation correlating GFR
and Serum Creatinine
GFR= 170 x [Serum Creatinine]-0.999 x [Age]-0.176 x [BUN]-0.17 x
[Albumin]-0.318
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NO NEED TO MEMORIZE!
BUN and Albumin values are optional when computing for the
EGFR
o 6-value Equation v. 4-value Equation (No BUN and albumin)
EGFR is affected by ethnicity and gender
o Caucasians (80mL/minute) vs. Negroes (97mL/minute)
o Additional Multipliers:
 Gender: Females (x 0.762)
 Race: Negroes (x 1.180)
The equation does not take into account actual muscularity
The above equation tends to underestimate GFR for near normal
creatinine clearance.
o Report only if creatinine clearance is > 60mL/minute
NKDEP RECOMMENDED MDRD EQUATION
 According to the National Kidney Disease Education Program,
EGFR derived from the MDRD equation is more accurate than
creatinine clearance measurements (Figure 7)
Figure 6. Other factors that affect Serum Creatinine levels
Figure 7. MDRD-predicted GFR vs. Actual GFR. Note that at GFR
levels above 60 ml/min/1.73m2 , predicted GFRs are overestimated
using the MDRD Equation.

NKDEP recommends that creatinine clearance measurement be
only performed on the following instances that suggest abnormal
basal creatinine production:
o Obesity
o Malnourishment
o Muscle-wasting diseases
B. ALTERNATIVES TO 24-HOUR URINE MODALITIES

Considered to be Estimates of the Glomerular Filtration Rate
(EGFR)
Figure 8. NKDEP recommended MDRD equations
COCKROFT-GAULT FORMULA
 GFR is estimated based on demographics: age, gender, weight,
and the serum creatinine
 Should NOT be used for the underweight or the morbidly obese
 A multiplier of 0.85 (highlighted below) is only used when getting the
EGFR of FEMALES (due to the lower muscle mass in females)
 If Serum Creatinine is given in mmol/L, divide the value by 88.4 to
arrive at the mg/dL measurement
Shen Franz Jerry
CHRONIC
KIDNEY
DISEASE
EPIDEMIOLOGY
COLLABORATION (CKD-EPI) FORMULA
 Uses the same variables as MDRD, but it does not overestimate
the true GFR, especially if it is >60mL/minute (refer back to
Figure 7)
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Lec 02: Renal Function Tests
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Figure 9. CKD-EPI Formula
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SCHWARTZ FORMULA
 Estimated GFR from 2 years of age to adulthood
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Figure 10. Schwartz Formula
OS 213
No gender difference in reference range
Levels rise with age over 50 years
Serum concentration mainly determined by GFR
Especially useful in moderate CKD (<60ml/min)
Ideal for renal replacement therapy (RRT)
o This does not exclusively refer to kidney transplants, but also
refers to other renal procedures as well.
In Europe: more dependable than serum Cr
o Can be used even for children and elderly (reflects better
estimates for these age groups)
o Proposed as improved GFR marker – more sensitive than serum
Cr; not affected by other factors like muscle wasting
Influenced by cancer, icterus and thyroid diseases
Cystatin C vs. Serum Creatinine*
*based on EDTA GFR
 Cystatin C more sensitive in “creatinine blind” early GFR loss
 Cystatin C assay less precise
 Cystatin C more expensive (£ 2-3 or ~₱150-200)
 Cystatin C may have malignant progression
o There is suggested upregulation of cystatin C in tumor
progression
o Expression of cystatin C observed in human and colon cancer
cell lines
o Cathepsins (which cystatin C inhibit) implicated in a variety of
models of malignant progression
o To date: still no effect seen in the progression of multiple
myeloma and proliferative hematogical disorders
 In hyperthyroids, there is a decrease in creatinine clearance but an
increase in cystatin C
Other settings (which Cystatin C can be used)
 CKD
 Pediatrics (esp 24-27 weeks or very young)
 Renal Tx monitoring
 Chemotherapy monitoring
 Pre-eclampsia
 Type 2 DM
 Spinal Cord injury
 Renovascular disease
 Myeloma
 Rheumatoid Arthritis on NSAIDS
Measurement of Cystatin C
 Measured by immunoassay
 Problem: still no international standard
 Generally free from spectral interferences (hemolysis, icterus,
lipaemia)
 Precision as good as creatinine
Figure 11. Normal GFR values by age
KIDNEY DYSFUNCTION AND GFR
 Kidney dysfunction can be classified based on the derived GFR
value.
 Staging:
o Stage 1 (>90mL/minute): structural damage or proteinuria
o Stage 2 (60-90mL/minute)
o Stage 3 (30-60mL/minute) – symptoms start to appear such as
anemia, hypertension, and fluid and electrolyte imbalances
o Stage 4 (15-30mL/minute)
o Stage 5 (<15 mL/minute): requires dialysis
 Stages 3-5: late stage of chronic renal disease
Monitoring function over time
 20 Pima Indians with type 2 diabetes
 All hyperfiltering
 Iothalamate GFR over 4 years
 Cystatin C
 MDRD
 C&G
Cystatin C and CKD
 Cystatin C detects CKD earlier than creatinine
 More sensitively predicts earlier complications of CKD
 Better markers for GFR are needed; cystatin C is a possible new
detector
 Maybe used for:
o Treatment monitoring
o Pediatric patients
o pregnancy
B. SERUM UREA
III. RENAL FUNCTION TESTS
A. CYSTATIN C
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Protein structure
o Mol. mass c.13 kDA
o basic protein
o 120 AAs, single pp. chain
Cysteine-protease inhibitor
Stable production rate by most nucleated cells
Freely filtered at glomerulus
Reabsorbed/ catabolized in the proximal tubule
Immunoturbidimetric / nepholometric particle-enhanced assays
Interference from turbidity and rheumatoid factors
Stable room temperature for 7 days
Shen Franz Jerry
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May be used as a marker, but it is also made in the liver (non-renal
influences: non-specificity is a problem)
Deamination of amino acids
Major route for N excretion
Filtered but major tubular reabsorption (esp. in low urine flow
rates or hypoperfusion)
BUN:creatinine ratio essentially asks Is the patient hypovolemic?
o BUN increases more than creatinine in
hypoperfused/hypovolemic states (prerenal azotemia)
Hypovolemia: Urea reabsorbed is more than 50%
and leads more fluid to be reabsorbed and restore blood volume
o Dehydrated states cause an increase in urea absorption
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Lec 02: Renal Function Tests
OS 213
o usually indicates the presence of nonalbumin proteins in the
urine, most commonly immunoglobulin light chains
Blood Urea Nitrogen (BUN)
 Reverse relationship with GFR, but many confounding factors
 Urea nitrogen can reabsorb paralleling with Na and H2O resorption
 BUN：Pcr = 15-20:1
 Also used to measure GFR
 However, it is a poorer measure of GFR than creatinine. It is not a
good measure of kidney function because it can be affected by:
protein intake, catabolism, liver function, GI bleeding, renal
perfusion, volume status.
o reabsorption of urea depends on volume status: the more
dehydrated, the more urea is absorbed
o urea clearance is only 60% of creatinine clearance
 BUN is a good measure of volume status
Figure 12. Urinalysis
C. NEW TUBULAR MARKERS
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New Biomarkers for assessing ACUTE kidney injury (AKI) – tubular
markers
2016B: Remember that creatinine clearance cannot be used in AKI
there should be steady state in measuring creatinine clearance
Urinary Neutrophil Gelatinase- Associated Lipocalin (NGAL)
o Most promising new biomarker
o Rises earlier than creatinine, making it an earlier marker
o Ann Intern Med 2008;148:810-819
Urinary Interleukin 18
o Am J Kidney Dis 2004;43:405-414
Urinary Kidney Injury Molecule-1 (KIM-1)
o J Am SocNephrol 2007;18:904-912
D. COMPARISON OF ACCURACY OF MARKERS
Least Accurate
Most Accurate
Urea (reabsorbed)
24-hr CCr
Creatinine
Cystatin C
CCr calculated from Cr
GFR calculated from Cr
3-hr CCr with Cimetidine
Direct GFR Measurement
Chromium-EDTA Clearance
Inulin Clearance
Iohexol Clearance
IV. URINALYSIS
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Major noninvasive diagnostic tool available
Should be performed in all patients with renal disease
Important in screening for disease routine test for every patient,
and not just for the investigation of renal diseases
Comprises a range of analyses that are usually performed at the
point of care rather than in a central laboratory.
One of the most common biochemical tests performed outside the
laboratory.
Examination of a patient's urine should not be restricted to
biochemical tests.
Supernatant tested for protein, glucose, heme pigments, pH and
concentration
o Dipsticks often used to detect abnormal pH, presence of protein
or hemoglobin, other abnormal constituents of urine, such as
glucose, bacteria and bilirubin
Examine midstream specimen within 30-60 minutes of voiding
o Urine should be placed in the ref if not examined immediately
after voiding because pH will turn alkaline. When it becomes
alkalinized you lose some of the casts.
Midstream specimen adequate in men
o Midstream and morning urine collection – ideal urine collection
because of concentrating ability is better measured (kasi
overnight) and all casts are presents.
Midstream specimen adequate in women
o External genitalia should be cleaned in women to avoid
contamination by vaginal secretion and flora
Centrifuged at 3000 rpm for 3 to 5 minutes supernatant poured
into separate tube small amount of sediment placed on slide
A significantly positive SSA (gold standard for albuminuria) test
PLUS a negative urine dipstick
Shen Franz Jerry
Urinalysis using Disposable Strips
 Biochemical testing of urine involves the use of commercially
available disposable strips When the strip is manually immersed
in the urine specimen, the reagents react with a specific component
of urine in such a way that to form color
 Color change produced is proportional to the concentration of the
component being tested for.
 Fresh sample = Valid sample
 To test a urine sample:
o Fresh urine is collected into a clean dry container
o The sample is not centrifuged
o The disposable strip is briefly immersed in the urine specimen
o The color of the test areas are compared with those provided on
a color chart
A. PHYSICAL CHARACTERISTICS
Color
 Note gross appearance, volume, and odor as well
 Normal color: straw
Table 3. Causes of Coloration of Urine
PINK-ORANGERED-BROWNRED
BLACK
ENDOGENOUS
CAUSES:
Methylene Blue
 Haemoglobin
 Hemoglobin
Pseudomonas
 Myoglobin
 Myoglobin
Riboflavin
 Phenolpthalein
 Red Blood Cells*
 Rifampicin
(Blood appears
darker in lower
pH)
 Homogentisic
acid (in
alkaptonuria)
 Melanogen/mela
nin
 Porphyrin (in
porphyria) – turn
brown black
when urine left
standing
BLUE GREEN
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EXOGENOUS
CAUSES:
 Beet root
 Imipenem/Levod
opa
 Methyldopa
 Nitrofurantoin
(yellow to brown)
*subject to microscopy to confirm if RBC as it can be caused by food changes
Turbidity (from 2015)
 Sign of infection or nephrotic syndrome
 Urine commonly becomes turbid on standing because of
precipitation of phosphates
 Hematuria makes urine slightly cloudy when red cell counts not quite
sufficient to produce visible color change
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OS 213
o decreased tubular reabsorption of protein (RBP, Albumin)
In chyluria, urine is milky and laden with fat and leukocytes; implies
a fistula between lymphatic system and the bladder; most common
cause of filariasis
Implicated by encephalopathy than selective shunts
Specific Gravity
 This is a semi-quantitative measure of concentration.
 Normal: 1.001 – 1.035
o <1.008 – diluted
o >1.020 - concentrated
 A higher specific gravity indicates a more concentrated urine.
 Assessment of urinary specific gravity usually just confirms the
impression gained by visually inspecting the color of the urine. (very
Specific Gravity
Turbidity
Normal Value
1.003 – 1.030
Clinical Value
1.000-1.005
D. Insipidus
> 1.030
Contrast dyes;
Glucose, mannitol
Clear
Infection,
crystalluria, chyluria
(milky white)
i.e. fistula
Table 4. Specific Gravity and Turbidity
Figure 13. Causes of Proteinuria
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Osmolality
 Osmolality serves as general marker of tubular function. Because
the ability to concentrate the urine is highly affected by renal
diseases.
 This is conveniently done by determining the osmolality, and then
comparing this to the plasma
 If the urine osmolality is 600mmol/kg or more, tubular function is
usually regarded as intact
 When the urine osmolality does not differ greatly from plasma (urine:
plasma osmolality ratio=1), the renal tubules are not reabsorbing
water
B. CHEMICAL CHARACTERISTICS
1. Urine pH
 Normal urine pH is 5.0-6.0
 Changes in pH have particular significance with renal calculi
o pH <5.0 typical in the presence of uric acid stones
o pH 7-8 in the presence of infection stones
 Urine pH may also alter urine microscopy
o Hemoglobin disappears more rapidly from erythrocytes in acidic
urine
o Both cells and casts disappear more quickly in an alkali urine
o So, urine must be tested within 30-60 mins (or, according to
2016, placed in 20°C to prevent this)
 Changes from normal range indicative of certain conditions
 Urine pH typically 5-6 in initial morning specimen
 pH may rise to 7.0 on vegetarian diet
 A value of 8.0 despite metabolic acidosis is characteristic of renal
tubular alkalosis (failure of urinary acidification; 2 types: proximal
and distal)
o Hypokalemia: Alkalosis
o Hyperkalemia: Acidosis
 8.0 also seen in urine infection with urea-splitting organisms (eg.
Proteus vulgaris)
Blood
Urinalysis dipstick
Urinalysis
microscopy
Table 5. Urinalysis Tests
Protein
Negative, trace, 1,
Negative, trace, 1,
2, 3
2, 3
Are the RBCs from
NA
the kidney
2. Proteinuria
 Hallmark for glomerular integrity (but can also have tubular
proteinuria as in multiple myeloma which has tubular albuminuria)
 The glomerular basement membrane does not usually allow
passage of albumin and large proteins. A small amount of albumin,
usually less than 25 mg/24 hours, is found in urine.
 When larger amounts, in excess of 250 mg/24 hours, are detected,
significant damage to the glomerular membrane has occurred.
 Quantitative urine protein measurements should always be made on
complete 24-hour urine collections.
 Causes:
o overflow (raised plasma Low MW Proteins, Bence Jones,
myoglobin)
o glomerular leak
Shen Franz Jerry


Major manifestation of renal disease and a dominant risk factor for
deterioration in most renal diseases for which risk factors have been
defined (vasculature of patient damaged = leakage of proteins even
in eyes, brain, etc.)
Usually reflects an increase in glomerular permeability that allows
filtration of normally nonfiltered macromolecules such as albumin
Normal urine protein excretion is < 150 mg/24 hr (140 mg/M2 in
children)
Greater part of normal urine protein is Tamm-Horsfall protein (30 –
50 mg) with some albumin and globulin
Routine detection is by dipstick testing but detects only albumin
Pure tubular or overflow proteinuria needs 24 hr urine collection or
urine tested with sulfosalicylic acid which detects all proteins
Assessment of Glomerular Integrity
 Injury of glomerular integrity results in the filtration of large
molecules which are normally retained and is marked as proteinuria:
the appearance of abnormal quantity of protein in the urine.
 Proteinuria may be due to: (note that not all are due to glomerular
disease)
o An abnormality of the glomerular basement membrane.
o Decreased tubular reabsorption of normal amounts of filtered
proteins.
o Increased plasma concentrations of free filtered proteins. (as in
multiple myeloma)
o Decreased reabsorption and entry of protein into the tubules
consequent to tubular epithelial cell damage.
 Measurement of individual proteins such as β2-microglobulin have
been used in the early diagnosis of tubular integrity.
o With severe glomerular damage, red blood cells are detectable
in the urine (hematuria), the red cells often have an abnormal
morphology in glomerular disease.
o Hematuria can occur as a result of lesions anywhere in the
urinary tract
Assessing Urine Protein Levels
 Since the amount of urine creatinine per day is relatively constant,
the concentration in urine provides an index of urine concentration
or dilution
 Solution: the protein: creatinine ratio or albumin/ creatinine ratio will
adjust for changes in urine concentration
 Albumin-creatinine ratio (ACR) represented as mg of albumin per g
of creatinine from 2 samples taken from a single patient
o Concentrated sample: 10mg/dl albumin per 100 mg/dl creatinine
Table 6. ACR and PCR
Protein
Albumin/creatinine ratio (ACR)
Random urine (children, adults)
Ma’am: Like taking 24h urine;
30-300mg/g: microalbuminuria
used to interpolate diagnosis
(metabolic syndrome, early
glomerulosclerosis)
Protein/creatinine ratio (PCR)
<0.2 g/g: normal
0.2-2 g/g: proteinuria
> 2g/g:nephrotic
Ways to Quantify the Amount of Proteinuria
 24h urine collection
o Albumin
 30-300mg/d: microalbuminuria
 >300mg/d: macroalbuminuria – kidney disease
o Protein
 150mg/d: proteinuria
 >3.5g/d: nephrotic
Page 7 / 11
Lec 02: Renal Function Tests

 Albumin/creatinine ratio
o Estimates 24-h urine albumin excretion
o Used to diagnose microalbuminuria
 Microalbuminuria present if ACR >= 3.5 mg/mmol in females
and >=2.5 mg/mmol in males
o Unlike the dipstick test, ACR is unaffected by variations in urine
concentration
o Also used to monitor kidney disease progression, response to
therapy, and risk of progression
 Prognositc marker in diabetes mellitus, hypertension, poststreptococcal glomerulonephritis
Urine electrophoresis – to determine type of protein
(SEE APPENDIX
PROTEINURIA)
2.
APPROACH
TO
A
PATIENT



 Very refractive hyaline casts can present in normal
patients. Most benign of all casts, difficult to see.
 Waxy casts - Pathonogmonic of nephrotic syndrome
 Fatty casts - Nephrotic syndrome (oval fat body casts)
D. CRYSTALS




WITH
C. URINE PROTEIN: URINE CREATININE RATIO

Calculates total protein to creatinine ratio (mg/mg) on a random
urine specimen
Ratio of <0.2 mg protein/ mg creatinine or <22mg protein/mmol
equates to urine protein
No need to do cumbersome 24h urine collection
If laboratory reports Upr/Ucr as mg protein/mg creatinine:
Table 6. ACR and PCR
Normal
< 0.1
Mild proteinuria
0.1 – 1.0
Moderate proteinuria
1.0 – 10.0
Heavy proteinuria
> 10.0






A. SPECIMEN COLLECTION







Full bladder
Periurethral area gently cleansed with water and labia held wide
apart
First 200 ml discarded and without interruption of urinary stream, a
midstream sample is taken
In males foreskin should be retracted
Glans cleansed with water before collecting midstream specimen
Catheterized sample should be obtained if with difficulty collecting
uncontaminated specimens
Needle aspiration in children
More accurate to count cells in uncentrifuged specimen
Semiquantitative techniques (counting number of cells per high
power field more commonly used although less accurate)










Microscopic examination of sediment from freshly passed urine
involves looking for cells, casts, fat droplets
Blood: haematuria is consistent with various possibilities ranging
from malignancy through urinary tract infection to contamination
from menstruation.
Red cell casts could indicate glomerular disease
Crystals
Leucocytes in the urine suggest acute inflammation and the
presence of a urinary tract infection.
F. URINE VOLUME

C. CASTS







Urinary casts are cylindrical structures produced by the kidney and
present in the urine in certain disease states.
They form in the distal convoluted tubule and collecting ducts of
nephrons, then dislodge and pass into the urine, where they can be
detected by microscope.
They form via precipitation of Tamm-Horsfall mucoprotein which is
secreted by renal tubule cells, and sometimes also by albumin.
Cast formation is pronounced in environments favoring protein
denaturation and precipitation (low flow, concentrated salts, low pH).
Tamm-Horsfall protein is particularly susceptible to precipitation in
these conditions.
Casts generally maintain their shape and composition as they pass
through the urinary system.
Although the most common forms are benign, others indicate
disease.
Various casts found in urine sediment as follows (SEE APPENDIX 3
FOR ILLUSTRATIONS AND DESCRIPTIONS):
o Erythrocyte Casts: Glomerular diseases
o Leukocyte Casts:Pyuria, glomerular disease
o Degenerating Casts: (in different stages of degeneration)
 Granular casts - Nonspecific (Tamm-Horsfall protein)
 Hyaline casts* - Nonspecific (Tamm-Horsfall protein)
Shen Franz Jerry
Presence of three or more RBCs per HPF in 2 of 3 samples
o In males, the presence of RBCs already qualifies as hematuria,
since RBCs are not expected to be present in the urine
Dipstick for blood detects peroxidase activity of erythrocytes
However, myoglobin and hemoglobin also will catalyze this reaction,
so positive test result may indicte hematuria, myoglobinuria, or
hemoglobinuria
Blood in the urine is never normal, but not everything that is
red is blood
Visualization of intact erythrocytes on microscopic examination of
the urinary sediment can distinguish hematuria from other
conditions. Microscopic examination also may detect RBC casts or
dysmorphic RBCs.
Hematuria is divided into glomerular, renal (i.e., nonglomerular), and
urologic etiologies
May be microscopic or macroscopic
The blood can be from any site along the urinary system.
Dysmorphic RBCs and RBC casts strongly suggest renal/glomerular
origin because these took time to travel to the kidney down to
tubules (Non-dismorphic are most probably from the tubules)
Blood, particularly painless hematuria, can be a sign of renal cell CA
(SEE APPENDIX 4. ALGORITHM FOR PATIENT WITH
HEMATURIA)
Table 8. Causes of heme negative red urine
Medications
Food Dye
Metabolites
Doxorubicin
Beets
Bile pigments
Chloroquine
Blackberries
Homogentidsic acid
Deferoxamine
Food Coloring
Melanin
Ibuprofen
Methemoglobin
Iron sorbitol
Porphyrin
Nitrofurantoin
Tyrosinosis
Phenazopyridine
Urates
Phenolphthalein
Rifampin
B. URINE SEDIMENTS

Urate – irregularly shaped
o Ammonium biurate – brownish
o Uric acid
Triple Phosphate – coffin-shaped
Calcium Oxalate – most common, envelope or rhomboid shaped
Amino Acids
o Cystine – hexagonal, hereditary disorder; due to IEM
o Leucine – fine needle-shaped
o Tyrosine
Sulfonamide
Cholesterol
E. HEMATURIA

V. URINE MICROSCOPY


OS 213




Water homeostasis is determined by several interrelated processes:
o Water intake and water formed through oxidation of food stuffs.
o Extra-renal water loss: insensible water loss via feces, and
sweating.
o A solute load to be excreted that is derived from ingested
minerals and nitrogenous substances.
o The ability of the kidneys to produce concentrated or dilute urine.
o Other factors such as vomiting and diarrhea become important in
various disease states; loss of ability to produce concentrated
urine is a feature of virtually all types of chronic renal diseases.
Important to know what is anuria and oligonuria.
To maintain water homeostasis, the kidneys must produce urine in a
volume precisely balances water intake and production to equal
water loss through extra renal routes.
Minimum urine volume is determined by the solute load to be
excreted whereas maximum urine volume is determined by the
amount of excess water that must be excreted
Causes of polyurea (>3L/day)
o Increased osmotic load, e.g due to glucose
o Increased water ingestion
o Diabetes insipidus: Failure of ADH production results in marked
polyuria, which stimulates thirst and greatly increases water
intake
o Nephrogenic diabetes insipidus: The tubules’ lack of response to
ADH/vasopressin has a similar effect
Page 8 / 11
Lec 02: Renal Function Tests
o
o
o
o
o
G. BILIRUBIN




Bilirubin exists in the blood in two forms, conjugated water soluble
and unconjugated.
Bilirubinuria indicates the presence of conjugated bilirubin in urine.
This is always pathological.
Conjugated bilirubin is normally excreted through the biliary tree into
the gutmechanical obstruction results in high levels of
conjugated bilirubin in the systemic circulationexcreted into the
urine
OS 213
Adequacy of parenchymal thickness
Abnormality of cortical contours or papillary appearance
Dilatation or blunting of calyces
Abnormal position or course of ureter
Reflux or congenital variations
H. UROBILINOGEN



In the gut, conjugated bilirubin is broken down by bacteria to
urobilinogen, or stercobilinogen.
Urobilinogen is found in the systemic circulation and is often
detectable in the urine of normal subjects. Thus the finding of
urobilinogen in urine is of less diagnostic significance than bilirubin.
High levels are found in any condition where bilirubin turnover is
increased, e.g. haemolysis, or where its enterohepatic circulation is
interrupted by, e.g. liver damage.
I. GLUCOSE AND KETONES
1. Glucose – detected in urine if serum glucose > 180 mg/dl
Figure 15. Intravenous Pyelogram. Notice the Staghorn calculi in
the left kidney
2. Ketones - products of fatty acid breakdown.
 Their presence usually indicates that the body is using fat to provide
energy rather than storing it for later use.
 This can occur in uncontrolled diabetes, where glucose is unable to
enter cells (diabetic ketoacidosis), in alcoholism (alcoholic
ketoacidosis), or in association with prolonged fasting or vomiting.
From 2015 & 2016 (not discussed):

Urinate immediately prior to the procedure to ensure the
bladder is empty; access to a vein will be placed in an arm.
An intial “scout” image will be taken while face-up.

Once the injection of contrast dye is complete, it is
necessary to remain still during the procedure, which may
take up to one hour. At the end of the procedure, you will
again be asked to urinate for a final image, to see how well
the bladder has emptied
J. NITRITE


This test depends on the conversion of nitrate (from the diet) to
nitrite by the action in the urine of bacteria that contain the
necessary reductase
A positive result points towards a urinary tract infection, but a
negative one does not point to the absence of UTI. (Bacteria may
not be able to convert nitrate to nitrite)
VI. IMAGING
PLAIN KUB XRAY






Identifies radiodense site of calcification (kidney stones–renal
calculi)
Can be in kidney, renal, pelvis, ureters or bladder
Cheap, simple, routine and available in most academic centres
However, shadows from bowels/ bones can obscure site of calculi
Little specific information; CT scan may be more definitive
Gives information on size, shape, and position of the kidneys,
presence of calcium in cyst, tumors, or stones can be detected
along with vascular or lymph node calcifications in the area
EXCRETION UROGRAPHY






Still used, but being replaced by ultrasonography
Give iodine containing contrast medium intravenously
Kidneys usually have smooth outlines 11-14 cm long
Can indicate scars/ masses
Small size may indicate chronic disease of kidney tissue or
vasculature
Good for tracking obstructions, but more accurate techniques are
available.
Problem with injecting dye intravenously:
If you have diminished kidney function, the dye will not be
excreted by the kidneys. Instead it will be pooled in your body
causing nephrotoxicity. Therefore it may cause further
damage to those already with impaired renal function.
ANTEGRADE PYELOGRAPHY





Involves injection with needle at level of renal pelvis (junction
between kidney and ureter).
Inject contrast medium to show where obstruction in tract occurs
Often used after ultrasound has shown there is a problem
Focuses on renal pelvis and ureters
Guided with CT or ultrasound; seldom used because of availability
RETROGRADE PYELOGRAPHY






Done following cystoscopy, inject contrast medium at bottom of
ureter
Track upwards to find blockages
Again, can be done after ultrasound or excretion urography
Very invasive
Requires general anaesthetic
In males, dye is injected directly into the urethra
Figure 14. Plain KUB. Calcium Stone/Calculi on right kidney
MICTURATING CYSTOURETOGRAPHY (MCU)
INTRAVENOUS PYELOGRAM




A dye is injected to visualize the following:
o Nephrogram – opacification of blood parenchyma of the
kidneys; depends on GFR dose and rate of contrast infusion
o Pyelogram – filling of the pelvocalyceal system
Nephron size ≥ 11 cm
L longer than R by 1.5 cm
Gives information on:
o Renal size, position, number, and presence of calcification
o Distorting intrinsic or extrinsic mass lesion
Shen Franz Jerry

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
You inject a dye and take shots while the patient is urinating
Catheterise bladder and instill contrast medium
Remove catheter and screen subject whilst they void to check for
any reflux or watch urethra and bladder empty.
Often combined with pressure studies
Not used if person has recurrent infection of urinary tract
CYSTOSCOPY


You insert a scope in the urethra and visualize the bladder
Direct inspection of interior of bladder (done with anesthesia)
Page 9 / 11
Lec 02: Renal Function Tests



Can also be followed by urodynamic studies where you can monitor
changes in pressure during filling and emptying
Can show exactly were the problem is in the urinary tract, and you
can take biopsies whilst you are in there
Cheap and usually available in most academic centres.

Higher doses of radiation

Superior to CT scan in the ability to detect tumor thrombus in a
major vessel and in distinguishing renal hilar collateral vessels
from hilar lymph node (esp. Renal CA)
Useful for differentiating adrenal mass lesions
Evaluation of patients with pheochromocytoma
Also called nuclear magnetic resonance (NMR)
Not usually used, but can image renal masses not identified by
previous methods and can monitor renal arteries
Image based on radiofrequency (RF) pulse returned from RFstimulated protons in magnetised tissues
No contrast agent, instead gadollinum is used
Accurate only for main vessels and their blood flows
Expensive, limited availability
Very versatile and can measure from many planes/angles, has
good contrast
Doesn’t use ionising radiation – less chance of biological damage
Cannot be used for those on dialysis because it can cause
nephrogenic systemic fibrosis
Can’t use near pacemakers
Cannot image bone or calcium
MAGNETIC RESONANCE IMAGING (MRI)











Figure 16. Cystoscopy
ULTRASONOGRAPHY







Best diagnostic modality for renal cyst
Most non-invasive test, because you don’t use any dye and you
don’t have to drink a lot of water
Better than Xrays since it avoids radiation and IV contrast mediumuses high frequency sound waves
Used to:
o Measure size of parts of renal system
o Check for blood vessel diameter
o Checking whether masses are cysts or solid/textured
o Measure perfusion, check for clots (uses Doppler shift in signal)
o Can also check bladder wall thicknesss, stones or emptying
Disadvantages:
o Lack of detail - poor specifitiy/sensitivity
o Cannot fully visualize adult ureter
o May miss small stones or those in ureters (<1 cm)
o Reliant on experience and interpretaion of the operator.
Normal kidney length is between 8.5 to 12 cm, measure from pole
to pole
Renal cortices about 1 cm in thickness, smooth in contour and not
echogenic
Figure 17. Ultrasound of the Kidney. Right shows colored UTZ
showing the blood vessels
OS 213


ARTERIOGRAPHY OR VENOGRAPHY









Gold standard for diagnosing primary disease of renal vessels
(e.g. renal infarction)
Use angiography to monitor blood vessels as in heart
Can also use digital subraction angiography (DSA)
DSA uses small doses of contrast medium to monitor blood flow in
nal vessels (venous or arterial)
Inject it into larger artery or vein near kidneys
Mainly used to monitor extrarenal or intrarenal arterial disease
Arteriorgraphy still the gold standard in renal imaging, but MRI
and CT are getting better
Invasive, but becoming more routine.
Less discomfort for subject, since doesn’t go through the more
embarassing “plumbing” system. Usually insert catheter through
small incision in groin (e.g. femoral vein)
Figure 18. Screening Arteriography. Visualization of the aorta and
its branches.
From 2016 (not discussed):

Difference at >1.5 cm in kidney stones – suggests
asymmetric renal disease

Simple Cyst: No internal echoes with sharply defined
smooth internal wall

Hydronephrosis: multioculated fluid collection within the
renal sinus.

Can be done first before subjecting patient to MRI, which
may exposed him/her to unnecessary danger
COMPUTED TOMOGRAPHY (CT)







Best used for detecting small stones and tumor
Spiral technology that collects images from volume of tissue, rather
than slice-by-slice
Xray fired from moving emmitter, measure by ring of detectors
Improved image resolution and can recontruct data from variety of
planes/ angles. Good for 3D imaging.
Good at finding masses/stone (even small stones <1-2 mm)
Uses dye to visualize arteries and veins
Generally useful for finding structural abnormalities, but may require
large volumes of contrast medium.
Shen Franz Jerry
Figure 19. Huge tumor arising from the upper pole of the left kidney.
Patient probably presented with severe hypertension because the tumor
is impinging on the renal vessels
Page 10 / 11
Lec 02: Renal Function Tests
Figure 19. Huge tumor arising from the upper pole of the left
kidney. Patient probably presented with severe hypertension
because the tumor is impinging on the renal vessels
RADIONUCLEIDE STUDIES







Used to complement ultrasound
99 mTc DTPA – Estimate GFR
99 mTc DMSA – Bound to tubules and provides information on the
location, size of functional renal tissue; better in evaluating the
tubules
131 I OIH – Secreted into the tubules and used to assess RPF
When you do a renal scan, it is like doing a GFR. You look at the
glomerulus and tubules.
In Differential GFR, you have to know the GFR of the left and right
kidneys. You do this when you are deciding what to operate.
When you are undecided, do you operate on the better or worse
kidney? Answer: It depends. When you are trying to save a patient
with a stone, you operate on the better kidney.
*DTPA= Diethylenetriaminepentaacetic acid
DMSA = 2,3 – Dimercaptosuccinic acid
OIH = Orthoiodohippurate
OS 213
Figure 21. Scintigraphy. Left shows normal kidney. Right shows renal
scarring.
STATIC SCINTIGRAPHY
 Performed using 99Tcm-DMSA, which is taken up by tubular cells.
 Uptake is proportional to renal function.
 Function evenly divided between kidneys.
 This technique good for looking for problems that only affect one
kidney as can detect imbalances in function.
 Normal kidneys show uniform uptake with smooth renal outline.
 Again, less invasive and tells us about actual function, but only gives
us a snapshot of what is going on and poor anatomical resolution.
SUMMARY



Wealth of techniques used to assess renal function
GFR estimates, urinalysis and imaging techniques added to a good
history and physical examination are essential not only in making a
diagnosis but in planning disease management.
From 2016: If there is inability to diagnose, a biopsy may be done.
END OF TRANSCRIPTION
INDICATIONS FOR NUCLEAR RENOGRAM
 Quantify total renal function – Through measurement of overall GFR
and RPF
 Quantify the percentage contribution of each kidney to overall renal
function – Good for differentiating the two kidneys in transplantation
screening.
 Detect obstruction
 Detect (+) or (-) of normal renal parenchyma in suspecting mass
lesion
 Evaluate renovascular disease
RENAL SCINTIGRAPHY


Uses gamma camera and can be divided into:
o Dynamic studies where kidney function monitored serially over
period of time, most often by using a radiopharmaceutical
excreted by glomerular filtration.
o Static studies involving imaging of tracer that is taken up and
retained by the renal tubule.
Uses ionizing radiations, so you would have to justify why technique
needed to be used.
DYNAMIC SCINTIGRAPHY
 99Tcm-DTPA excreted by glomerular filtration
 123I-Hippuran is both filtered and excreted by tubules.
 Following venous injection with tracer, emissions from kidney
recorded and computer analyses time-activity curves.
 Allows examination of renal blood perfusion, glomerular filtration,
transit through kidney and outflow from urinary tract.
 Can give false-positive or false-negative results.
 Less invasive and can give a lot of information about whole urinary
system over time.
 Can monitor more realistic physiological conditions.
Shen Franz Jerry
Page 11 / 11