Download RENAL TUBULAR FUNCTION

INVESTIGATION
OF RENAL
FUNCTION
肾功能的检测
武汉大学中南医院检验系、检验科 涂建成
电话：027-67812989,13507119120
E-mail：[email protected]
Ⅰ - STRUCTURE AND
FUNCTIONS OF THE KIDNEY
肾脏的结构与功能
Anatomical Location and Gross
Structure
Kidney: Cross-Section
A - STRUCTURE OF THE KIDNEY
肾脏的结构
The functional unit in the kidney is the nephron(肾单位).
Each kidney contains more than one million (1,200,000)
nephrons.
The different basic parts of the nephron are :
 the renal corpuscle（肾小体）,
 the renal tubules（肾小管）
 and the collecting duct（集合管）.
Glomerulus:肾小球
Proximal tubule:近曲小管
Distal tubule:远曲小管
Collecting duct:集合管
Loop of Henle:髓袢
Glomerular capillaries:球小动脉
renal capsule
renal corpuscle
glomerulus
proximal tubule
nephron
renal tubules
loop of Henle
distal tubule
collecting duct
Diagrammatic representation of the different parts of the nephron
B - FUNCTIONS OF THE KIDNEYS
(肾脏的功能)
The kidneys are the major organs responsible for
maintaining a constant level of composition and the
volume of the body fluid homeostasis(动态平衡)
They have several functions, which can be summarized as
the following two (2) basic functions:
 Urinary function（泌尿功能）
 Endocrine function (内分泌功能)
(1) Urinary function（泌尿功能）
 Elimination of waste products of metabolism （排泄代
谢废物）from the blood and their excretion in urine.
(e.g. urea 尿素 from protein metabolism, uric acid尿
酸 from nucleic acids, creatinine 肌 氨 酸 酐 from
muscle creatine肌氨酸).
 Removal of foreign chemicals from the blood
and their excretion in urine (e.g. drugs, pesticides 杀虫
剂, food additives 食品添加剂) .

Regulation of water content, mineral composition(electrol
ytes), and acidity of the body by excreting substances in a
n amount adequate to achieve total body balance and main
tain normal concentration in the extra-cellular fluid. (调节
水、电解质以及酸碱平衡）

Retention of nutrients such as proteins, glucose and water
(营养物质的保留 )
ERRR(Elimination-Removal-Regulation-Retention)
(2) Endocrine function(内分泌功能)
Kidneys secrete some hormones such as:
 erythropoietin, EPO 促红细胞生成素
controls erythrocyte production, 造血功能
 renin肾素(catalyzes the formation of angiotensin I血管
紧张素I from angiotensinogen in a series of biochemical
reactions that result in the stimulation of aldosterone 醛
固酮 synthesis),
 aldosterone (plays a key role in the control of sodium
balance调节钠离子平衡)
 antidiuretic hormone, ADH抗利尿激素 or vasopressin
血管加压素 influences water and sodium balance,
maintain blood pressure维持血压 。
 Parathyroid hormone, PTH甲状旁腺(激)素 promotes
tubular reabsorption of calcium and phosphate excretion,
and the synthesis of 1,25 dihydroxy-cholecalciferol (1，
25-二羟基维生素D3)
 1,25 dihydroxy-cholecalciferol
reabsorption by the gut 肠
regulates
calcium
（五）肾髓质渗透梯度形成和维持示意图
Ⅱ- INVESTIGATION OF
RENAL FUNCTION
肾功能的检测
 It is not easy to assess renal function without any tests or
investigations. However, a number of symptoms症状
may suggest disturbance of kidney function：frequency
of micturition频尿 (polyuria多尿and nocturia夜尿症 ),
oliguria少尿症, anuria无尿症and hematuria血尿症etc.
 The investigation of renal function consist mostly of the
evaluation of glomerular filtration and tubular
reabsorption and secretion function (肾功能的检测主要
包括肾小球的滤过与肾小管的重吸收和分泌功能的
检测)
A - RENAL GLOMERULAR
FILTRATION FUNCTION
肾小球滤过功能

Glomerular Filtration Rate

creatinine clearance

Serum creatinine and urea

Proteinuria

Urine collection

Other tests of glomerular function
1 - Tests of glomerular function
The thin walls of the glomerular basement membrane基底
膜covering the capillaries (毛细管 ) acts as molecular
filters(分子滤过膜), allowing small compounds to filter
out of the capillaries into the glomerulus（fig 1）.
Glomerular Filtration Rate
肾小球滤过率
The glomerular filtration rate (GFR，肾小球滤过率）is
the rate (速度), at which the plasma is filtrated by the
glomerulus. It is approximately 140 ml/min in the
average-sized 70kg healthy male. Estimation of GFR is an
extremely important tool in the assessment of renal
function.
 A normal GFR depends on normal renal blood flow (正
常肾血流量), normal blood pressure, body size and
age.
 If the GFR falls due to limitation of the renal blood
supply, or the destruction of nephrons by renal disease,
there is retention of the waste products of metabolism
in the blood (代谢废物累积).
The concept of Clearance 肾清除率
A clearance of a substance is the volume of plasma
from which a measured amount of that substance is
eliminated into a volume of urine per unit of time (min).
UxV
Volume of plasma =
P
Where U is the concentration of the substance in the
urine (mmol/l), V is urine flow speed (ml/min) in a
given time (liters per 24h),and P is the plasma
concentration of the substance.
Example of the calculation of the
creatinine clearance (肌酐的肾清除率)
Case History 10
A male aged 35 presenting with loin pain （腰痛）has
a serum creatinine of 150μmol/L. A 24-hour urine of
2160 ml is collected and found to have a creatinine
concentration of 7.5 mmol/L.
Calculate the creatinine clearance.
UxV
It is calculated using the formula : C =
P
U is the urine concentration of creatinine and equals to 7.5
mmol/L = 7500μmol/L ,
V is the urine flow-rate (尿流速), it is expressed in
mililiter per minute (ml/min) and equals to
2160
V =
24 x 60
= 1.5 ml/min
P is the plasma concentration of creatinine and equals to
150μmol/L, so
7500 x 1.5
C =
150
= 75 ml / min
In practice, the creatinine clearance value obtained must be
corrected for height and weight; sex and age of the
individual before it can be used to identify patients with
impaired renal function, the formula becomes:
UxV
C =
X
P
1.73
A
Where 1.73 and A are the standard and the patient’s body
surface area （体表面积）respectively. A can be
determined from the patient’s height and weight with a
nomograph (测算图) or DuBois formula:
Log A (m2) = 0.425 Log (weight) (kg) + 0.725 Log (height) (cm) – 2.144
The maximum rate that the plasma can be “cleared” of any
substance is equal to the GFR. It can be calculated from the
clearance of some plasma constituents which is freely
filtered (自由地滤过) at the glomerulus, and is neither
reabsorbed nor secreted in the tubule.Examples: inulin(菊
粉) a plant fructose polysaccharide , creatinine（肌酐)，
mannitol（甘露醇), Cr-EDTA etc.
(2) Serum creatinine and urea
血肌酐和尿素浓度测定

The creatinine 肌酐is the metabolite (代谢物) of the
creatine phosphate (磷酸肌酸) of the muscle(肌肉). It
is mostly filtered by the glomerulus, but not reabsorbed
by the tubules. (only a small quantity by the proximal
tubule).


The urea 尿素 is the metabolite of the body proteins
that cannot be broken down into small molecules. Its
serum concentration depends on the body proteins
catabolism ( 分 解 代 谢 ), the diet proteins and the
excretion ability of the kidneys. It is freely filtered by
the glomerulus, but 50% are reabsorbed by the tubules
Serum creatinine and urea concentrations ，on the
certain degree，can reflect the glomerular filtration
ability.They are convenient (方便), but insensitive (低
灵敏度) to measure of glomerular function:

the GFR must fall to about half its normal value before a
significant increase in serum creatinine becomes apparent.

because plasma creatinine levels are related to an
individual’s muscle mass, the reference intervals will
vary with age and body size.

dietary protein intake affect serum urea concentration.


gastrointestinal bleeding (胃肠出血) will cause rising
of serum urea
urea is reabsorbed in the tubules.
So most laboratories measure both serum creatinine
and urea and their ratio（比值） is useful in the
investigation of renal disorders.
 High-performance liquid chromatography was used to
measure GFR directly in a critically ill patient with
acute renal failure. This approach involved evaluating
the elimination kinetics of nonionic 非离子物质排泄
动力学 contrast material administered intravenously
for radiologic imaging.
(3) Proteinuria (蛋白尿)

When large amount of protein (more than 150 mg/24h)
are detected in a urine specimens, that means,
significant damage to the glomerular membrane has
occurred. It is called glomerular proteinuria (肾小球性
蛋白尿).

Proteins tested are macromolecules such as albumin(白
蛋白), transferrin（转铁蛋白), IgG, IgA, IgM, 2-
macroglobulin (2-巨球蛋白) etc.
(4) Urine collection（尿的收集）

An accurate urine collection is very important in
the determination of creatinine clearance.
(5) Other tests of glomerular function
 Determination of uric acid (UA)尿酸
It is the end product of purine 嘌呤 nucleotide
metabolism and it is excreted along with the urine.
Hyperuricemia高尿酸血症 is associated with renal
disease, but it is usually considered a marker of renal
dysfunction rather than a risk factor for progression.
Determination of serum cystatin C
（半胱氨酸蛋白酶抑制剂 C ）
Cystatin C is a cysteine proteinase inhibitor半胱氨
酸蛋白酶抑制剂, which is produced by most
nucleated cells.
More recently, the serum concentration of cystatin C
has been measured as a potentially superior index of
kidney function. （Cystatin C是反映肾小球滤过
率的灵敏标志物）
Biomarkers for the early detection of
acute kidney injury.
Nguyen MT, Devarajan P.
Nephrology and Hypertension, MLC 7022, Cincinnati Children's Hospital Medical Center,
 Acute kidney injury (AKI), previously referred to as acute
renal failure (ARF), represents a persistent problem in
clinical medicine. Despite significant improvements in
therapeutics, the mortality and morbidity associated with
AKI remain high.
 A major reason for this is the lack of early markers for
AKI, CK to troponins in acute myocardial disease, and
hence an unacceptable delay in initiating therapy.
Fortunately, the application of innovative technologies
such as functional genomics and proteomics to human and
animal models of AKI has uncovered several novel genes
and gene products that are emerging as biomarkers.
The most promising of these are chronicled in this article.
These include a plasma panel [neutrophil gelatinaseassociated lipocalin (NGAL) and cystatin C] and a urine
panel [NGAL, interleukin 18 (IL-18), and kidney injury
molecule 1 (KIM)-1].
As they represent sequentially expressed biomarkers, it is
likely that the AKI panels will be useful for timing the
initial insult and assessing the duration of AKI.
Based on the differential expression of the biomarkers, it is
also likely that the AKI panels will distinguish between the
various types and etiologies of AKI. It will be important in
future studies to validate the sensitivity and specificity of
these biomarker panels in clinical samples from large
cohorts and from multiple clinical situations.
Scand J Clin Lab Invest. 2007;67(2):179-90
Cystatin C reduces the in vitro formation of
soluble Abeta1-42 oligomers and protofibrils.
Selenica ML, Wang X, Ostergaard-Pedersen L, Westlind-Danielsson A, Grubb A.
Disease Biology, H. Lundbeck A/S. Copenhagen. Denmark.
There are an increasing number of genetic and
neuropathological observations to suggest that cystatin C,
an extracellular protein produced by all nucleated cells,
might play a role in the pathophysiology of sporadic
Alzheimer's disease (AD).
Recent observations indicate that small and large soluble
oligomers of the beta-amyloid protein (Abeta) impair
synaptic plasticity and induce neurotoxicity in AD. The
objective of the present study was to investigate the
influence of cystatin C on the production of such
oligomers in vitro.
Co-incubation of cystatin C with monomeric Abeta1-42
significantly attenuated the in vitro formation of Abeta
oligomers and protofibrils, as determined using electron
microscopy (EM), dodecyl sulphate polyacrylamide gel
electrophoresis (SDS-PAGE), immunoblotting, thioflavin
T (ThT) spectrofluorimetry and gel chromatography.
However, cystatin C did not dissolve preformed Abeta
oligomers. Direct binding of cystatin C to Abeta was
demonstrated with the formation of an initial 1:1 molar
high-affinity complex.
These observations suggest that cystatin C might be a
regulating element in the transformation of monomeric
Abeta to larger and perhaps more toxic molecular
species in vivo.
2 - Glomerular dysfunction
They are two basic types of disease resulting from
glomerular dysfunction:


glomerular nephritis
(肾小球肾炎)
and nephrotic syndrome（肾病综合征） .
(1) Glomerular nephritis

It is caused by an acute inflammation of the glomerular
basement membrane. That yields to the decrease of the
GFR and the urine formation (oliguria 少尿) or no urine
formation (anuria 无尿).

The decrease of renal function results in an increase in
blood concentrations of waste products（废物）.

There is also increased leakage of RBC (hematuria血尿)
and protein into the urine (proteinuria).
(2) The nephrotic syndrome

It can result from many causes, including infectious
agents(传染源), toxins (毒素) , allergens (致敏源) and
immunological destruction of glomerulus.

It is also secondary to other diseases like cancers and
diabetes. It is defined clinically by a massive protein
loss into urine with edema 水肿, hypoalbuminemia 低
白蛋白血症, hyperlipidemia 高脂血症 and lipiduria.
Summary

The capacity of the kidneys to filter plasma at the
glomeruli can be assessed by measuring the creatinine
clearance, which approximates to the glomerular
filtration rate.

Serum creatinine concentration is an insensitive index of
renal function, as it may not appear to be elevated until
the GFR has fallen below 50% of normal. Once the
serum creatinine is found to be abnormal, changes in
concentration reflect changes in GFR.

Large amounts of protein in a urine specimen may
indicate glomerular damage.

The biggest error in the measurement of creatinine
clearance, or of the daily excretion of any metabolite
lies in the collection of the timed urine sample.
B - RENAL TUBULAR
FUNCTION
肾小管的功能

Whereas the glomeruli provide an efficient filtration
mechanism for clearing the body of waste products
and toxic substances, tubular reabsorption（肾小管的
重吸收） prevent the lost of important constituents
such as water, sodium, glucose, amino acids, calcium,
chloride and potassium from the body.

The excretion (排泌) is the process by which the
epithelial cells (上皮细胞)of the tubules and the
collecting duct transfer their products (H+ , NH3) or some
blood substances (paraaminohippurate, PAH 对氨基马
尿酸 Phenolsulfonphthalein PSP酚红) to the renal
tubular cavity（肾小管 腔）.

The kidneys excrete H+ and retain Na+ (肾脏排H+保Na+ )
1 - Investigation of tubular function
Include investigation of the following functions :

the tubular reabsorption
TRS重吸收率, Fe排泄分数, TmG葡萄糖最高重吸
收率 etc.

Excretion
PSP酚红排泄试验, TmPAH对氨基马尿酸最大排泄
试验etc.

water and electrolyte regulation specific gravity尿
比重, osmolality尿渗透压

acid base regulation H+ total excretion, acid load
test酸负荷试验, base load test碱负荷试验
(1) Osmolality measurements in
plasma and urine.

To assess the renal tubules’s ability to reabsorb water,
or the kidney’s ability to produce a concentrated urine,
the urine osmolality尿渗透压 is determined and then
compared to the plasma’s 血浆渗透压.

If the tubules and collecting ducts are working
efficiently, and if Arginine Vasopressine抗利尿激素
(AVP) is present, they will be able to reabsorb water.

So in normal individuals on an average fluid intake the
urine/plasma osmolality ratio is usually between 1.0 and
3.0. When this ratio is 1.0 or less, the renal tubules are
not reabsorbing water.
(2) The water deprivation test
禁水试验

To find the cause of excessive polyuria, a patient is
deprived of any fluid intake for 24-hours period, with
measurement of the osmolality of all the urine specimens
passed during the second 12 hours of the test. The
osmolality should be greater than 700 mmol/kg and
urine/plasma osmolality ratio should be 2.0 or above.

In polyuria of diabetes insipidus尿崩症, where the
hormone AVP is lacking, the ratio will remain
between 0.2 and 0.7 even after fluid restriction.

Administration of AVP as a synthetic analogue
(DDAVP) will result increasedurine concentration.But
in nephrogenic diabetes insipidus, there is no response,
due to the deficiency of AVP receptors.
(3)The acid load test 酸负荷试验

It is used for the diagnosis of renal tubular acidosis.
Ammonium chloride ( 氯 化 铵 )is administered orally in
gelatin凝胶capsules, urine samples are collected for the
following 8 hours.

With normal renal function, the pH of at least one sample
should be less than 5.3. In a difficult diagnosis, if necessary,
the excretion rates of titratable acid and ammonium ion, and
serum bicarbonate concentration, are all measured.
(4) Urinalysis 尿分析

The urinalysis can provide extremely important
information about renal function and presence of disease
states. It includes: urine physical examination, its
microscopic examination and biochemical analysis.

Urine physical examination
Its color, volume, clarity and its specific gravity .

Microscopic examination of urine
The urine microscopic examination for cells,
casts, crystals, bacteria, or parasites is a critical
procedure

Biochemical analysis
Include pH, osmolality, protein, urea, creatinine,
glucose, nitrogens etc.
2 – Tubular dysfunction

Defects in tubular function result in a reduction of the
tubules ability to reabsorb specific biochemicals. This
in turn can lead to an inability to produce
concentrated（浓缩） or dilute（稀释） urine and
affect electrolyte（电解质） and acid-base balance
（酸碱平衡）.
(1) Renal tubular proteinuria

It is the result of an inabilily of the proximal tubule to
reabsorb small amounts of low molecular weight protein
(β2 microglobulin 微球蛋白 and α1 microglobulin )
normally filtered through the glomerulus.

This can result from genetic abnormalities or tubular
damage.
(2) Renal tubular acidosis
肾小管酸中毒

Impaired secretion of hydrogen ions in the distal
tubule远端小管or reabsorption of bicarbonate ions
(HCO3-) in the proximal tubule近端小管can lead to
chronic metabolic acidosis慢性代谢性酸中毒.
Distal tubular acidosis (Type – I)

In type I renal tubular acidosis (RTA), the ability to
develop a hydrogen ion gradient梯度 across the distal
tubule is impaired, leading to an impair excretion of
hydrogen.

So the patients are unable to reduce their urine pH below
6.5. It may be an inherited or acquired disorder . It is
often associated with hypercalciuria高钙尿症,
hyperkalemia 高钾血症 and hyperuricemia 高尿酸血
症。
Proximal tubular acidosis (Type –II)

In type II RTA, the capacity of the proximal tubules to
reabsorb bicarbonate （HCO3- ）碳酸氢盐 is
decreased, so that urine pH is > 7 at normal levels of
plasma HCO3-. Instead of bicarbonate ，chloride氯化
物 is reabsorbed leading to a hyperchloremic acidosis高
氯性酸毒 .

It is often associated with several inherited diseases such
as Fanconi syndrome 范康尼综合征, multiple myeloma多
发性骨髓瘤, vitamin D deficiency, and chronic
hypocalcemia低血钙症 with secondary
hyperparathyroidism续发行甲状旁腺功能亢进

Renal tubular acidosis Type – III is the combination of
types I and II and is very rare.
Renal tubular acidosis Type -Ⅳ

In this case, there is aldosterone deficiency醛固酮缺乏
due to the aldosterone receptor defects, nephrotoxic
drugs 肾毒药, amyloidosis 淀粉样变性病and exposure
to heavy metal重金属 which block aldosterone action:
 this reduces potassium (K) excretion, causing
hyperkalemia血钾过多 , which reduces ammonia
(NH4+) production and acid (urea and H+) excretion by
the kidney. This is largely responsible for the acidosis.
 bicarbonate reabsorption by renal tubule is also
impaired
(3) Glycosuria 糖尿病

Normally, the body excretes glucose in the urine only when
glucose levels in the blood are very high, and when glucose
renal threshold肾阈 (the capacity for the tubules to reabsorb
glucose) is reached.

In most healthy people, glucose that is filtered from the
blood by the kidneys is completely reabsorbed back into the
blood. In pathological conditions, glucose may be excreted
into the urine despite normal or low levels of glucose in the
blood. This happens because of a specific lesion损伤in the
tubular cells that decreases the reabsorption of glucose. It is
call renal glycosuria肾性糖尿病 .

Renal glycosuria may be a hereditary condition. It is
also associated with other disorders of tubular function
like Fanconi syndrome.

Diagnosis is made by demonstrating glucose in the
urine after an overnight fast整夜禁食 in a patient
with normal glucose tolerance葡萄糖耐量.
(4) Aminoaciduria 氨基酸尿症

Normally,amino acids in the glomerular filtrate are
reabsorbed in the proximal tubules. But when the
plasma concentration exceeds the renal threshold, or
when there is specific failure of normal tubular
reabsorption mechanisms,amino acids are present in
urine in excessive amount. Example: cystinuria 胱氨酸
尿症。
(5) Specific Tubular defects
The Fanconi syndrome 范康尼综合征
 It is defined as a generalized tubular defects such as
renal tubular acidosis, aminoaciduria and tubular
proteinuria.
 It can occur as a result of heavy metal poisoning, or from
the effects of toxins and inherited metabolic diseases
such as cystinosis胱氨酸病 that reduces the absorption
of certain substances in proximal tubule, leading to
losses of glucose, amino acids, phosphate, and proteins
along with a metabolic acidosis.
Renal stones 肾结石

Renal stones (calculi) produce severe pain and
discomfort and are common causes of obstruction阻
塞 in the urinary tract .To investigate why they have
formed, their chemical analysis is necessary.
Following are the different types of stones:

Calcium phosphate: it may be a consequence of primary
hyperparathyroidism 甲状旁腺功能亢进 or renal tubular
acidosis.

Magnesium, ammonium and phosphate: these are
often associated with urinary tract infections.

Oxalate 草酸盐: may be a consequence of hyperoxaluria
高草酸尿,

Uric acid尿酸: may be a consequence of hyperuricaemia
高尿酸血症

Cystine: they are rares, characteristics of Cystinuria 胱氨
酸尿症.
Summary





Chemical examination of urine is just one aspect of
urinalysis.
A comparison of urine and serum osmolality measurements
will indicate if a patient has ability to concentrate urine
Specific tests are available to measure urinary concentrating
ability and the ability to excrete an acid load.
The presence of specific small proteins in urine indicates
tubular damage.
Chemical analysis of renal stones is important in the
investigation of their aetiology.
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