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AN INTRODUCTION TO
LABORATORY TESTS
AN INTRODUCTION TO
LABORATORY TESTS


Aim - introduction to laboratory tests of clinical and
diagnostic importance - biochemistry and haematology
Use?
 Assist doctor in making a diagnosis and monitoring treatment
 Assist pharmacist in assessing and monitoring drug treatment

Individual tests may provide insufficient information consider pattern of tests within a group


Single tests are of less value than a series - show trends
Expressed as a reference range - based on the assumption
that 95% of the population are normal
REFERENCE VALUES
1. RENAL FUNCTION TESTS

Serum Creatinine, Creatinine Clearance,
Urea
– Used to give an estimate of glomerular filtration
rate (GFR)
– GFR gives an indication of the efficiency of the
kidney and is decreased in renal impairment
– In practice, this is crucial information to determine
drug handling. Renally cleared drugs and
metabolites will accumulate in renal impairment
– Some drugs may reduce GFR e.g. NSAIDs and
aminoglycosides
1. RENAL FUNCTION TESTS

Serum Creatinine (Cr)
– Reference range 80 -150 micromoles/L
– Creatinine is a major metabolite of creatine
phosphate, a major constituent of muscle.
– Excreted almost exclusively by glomerular filtration
– freely filtered.
– GFR results in creatinine

Creatinine Clearance (CrCl)
– Renal impairment if< 50ml/min
– Serum creatinine can be used in the
Cockroft-Gault equation to estimate creatinine
clearance. GFR approximates to CrCl
COCKROFT and GAULT
EQUATION
Cr Cl = (140 - age) x Wt (kg) x F
Cr
Units are mls/minute
Cr = serum creatinine in micromoles/litre
F = 1.23 for males, 1.04 for females
1. RENAL FUNCTION TESTS

Urea (4.2-6.4mmol/L)
– Also known as blood urea nitrogen, BUN.
– Used to estimate renal function, but poor
measure of minor degrees of renal
impairment as it is influenced by other
factors.
– End product of protein metabolism. (High
protein diet increases urea)
– Usually measured as urea and electrolytes
(U&Es)
1. RENAL FUNCTION TESTS
HIGH SERUM CREATININE
signifies
GFR
 Renal impairment

RENAL IMPAIRMENT
Grade
GFR
(Creatinine Clearance)
ml/min
Mild
20-50
Moderate 10-20
Severe
<10



Serum
Creatinine
micromoles/L
150-300
300-700
>700
Renal impairment is arbitrarily divided into 3 grades ( see BNF)
Glomerular Filtration rate, measured by creatinine clearance
Note - definitions vary. Consult product literature for specific
drugs
2. ELECTROLYTES
Sodium, potassium, calcium, phosphate,
glucose
 Sodium
– Main extracellular cation. Osmolality of ECF is
largely determined by sodium and associated
anions
– Intimately linked with distribution of water between
intra and extracellular compartments (ICF and
ECF). Reflects fluid status of patient
– Changes in body sodium content result in changes
in ECF volume
– Reference value 133-144mmol/L
2. ELECTROLYTES
TOTAL BODY WATER
2. ELECTROLYTES
INTRA and EXTRA CELLULAR
FLUID
2. ELECTROLYTES
Hyponatraemia
Indicates an increase in free water in
ECF
 Caused by

– Sodium (and water) loss e.g.diuretics
– Water retention in excess of sodium e.g.
carbamazepine, tricylclics
– Symptoms if Na<120mmol/L – headache,
nausea, cramps, confusion
2. ELECTROLYTES
Hypernatraemia


Indicates a loss of free water and an increase
in sodium
Caused by
– Excessive water loss, or combined loss of water
and sodium with predominant water loss e.g.
diarrhoea in infants
– Unlikely to be caused by sodium excess - thirst
compensates

Symptoms at Na>160mmol/L - thirst, mental
confusion
coma
2. ELECTROLYTES
 Potassium
– Principal intracellular cation (<2-3% in
ECF)
– Involved in muscle excitation and cardiac
function. Body sensitive to changes in
serum potassium.
– Reference values 3.5 - 5 mmol/L
– Hypo - reduced muscle activity,
arrhythmias, mental slowing.
– Hyper - ventricular fibrillation and cardiac
arrest.
2. ELECTROLYTES
Hypokalaemia



Decreased potassium
Serious at <2.5mmol/L
(reference range 3.5-5)
Caused by
– Diuretics (loop and thiazide)
– Loss from GI tract (diarrhoea, vomiting)
– Shift into cells (insulin, salbutamol)
2. ELECTROLYTES
Hyperkalaemia



Increased potassium
Serious at >6.5 mmol/L
(reference range 3.5-5)
Caused by
–
–
–
–
Potassium sparing diuretics
Acute renal failure
Catabolic states e.g. diabetic ketoacidosis
Vast intracellular damage – cell lysis, release of K
3. LIVER FUNCTION TESTS
No specific test to determine degree of
liver impairment
 Important to look for a pattern using the
following tests

– ALP
– AST and ALT
– GGT
– Bilirubin
3. LIVER FUNCTION TESTS

Alkaline Phosphatase (ALP)
– Found in cells lining the bile duct – rise usually signifies
cholestasis [c] (obstruction to flow in bile duct)

Aspartate aminotransferase (AST) and
Alanine aminotransferase (ALT)
– Found in hepatocytes – rise usually signifies
hepatocellular damage [h]

Gamma-glutamyl transferase (GGT)
– Synthesis of the enzyme induced by alcohol and drugs.
Rise usually signifies hepatobiliary disease [hb]
3. LIVER FUNCTION TESTS

Bilirubin
Breakdown product of haemoglobin

Rise in UNCONJUGATED form usually signifies
» haemolysis (increased RBC destruction), or
» direct hepatocellualr damage.

Rise in CONGUGATED form usually signifies
» cholestasis - obstruction to bile flow

A rise in both CONJUGATED & UNCONJUGATED
bilirubin suggests
» mixed hepatocellular damage and cholestasis.
 Changes in LFTs may be due to disease process
(e.g. gallstones, hepatitis) or due to drugs
(e.g. chlorpromazine [h,c], flucloxacillin [c]).
3. LIVER FUNCTION TESTS
BILIRUBIN and UROBILINOGEN