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Summary An approach to understanding Liver Function Tests
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These provide a summary to understanding liver function tests.
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Chemical Pathology – Liver Function TestsThe following are looked at when assessing liver function:
- Bilirubin
o Unconjugated
o Conjugated
- Urine Urobilinogen
- Liver Enzymes
o Transaminases
AST
ALT
o Lactate Dehydrogenase
o ALP
o GGT
- Plasma Proteins
o Albumin
o Clotting factors
o Immunoglobulins
o AFP
- Plasma Ammonia
,Bilirubin:
Two forms are measured:
1.) Conjugated Bilirubin (aka Direct-reacting)
2.) Unconjugated Bilirubin (aka Indirect-reacting)
Lets us review the movement of bilirubin in the body:
- Haem broken down by the RES cells in the spleen
- (Unconjugated) Bilirubin produced
- This is attached to albumin which can be transported in the plasma
- NOTE: unconjugated bilirubin is found in plasma
- This is then taken to the liver and leaves the blood plasma
- Once in the hepatocytes, it becomes conjugated bilirubin
- This is then excreted into the duodenum
- In the colon it is converted into urobilinogen
- NOTE: conjugated bilirubin is not normally found in the blood plasma
When measuring the blood plasma (or serum) for bilirubin, the following should be noted:
- The normal total bilirubin should be <17 µmol/l
- This bilirubin will all be unconjugated of course
When things go wrong…
1.) ↑ unconjugated bilirubin in blood plasma:
- This may be due increased bilirubin production
o this is the case in haemolytic disorders
o this is the case in ineffective erythropoiesis
o These are your pre-hepatic liver disorders
- This may be due to decreased uptake or conjugation of bilirubin by the liver.
o This would occur in generalized hepatocellular dysfunction (thus the liver can’t carry out
its function of conjugating the bilirubin)
o This would also occur in specific rare inherited syndromes
Gilbert’s Syndrome – mutation in the conjugation enzymes
Criggler Najjar Syndrome - mutation in the conjugation enzymes
, When measuring the urine for bilirubin, the following should be noted:
- Normal urine should contain no bilirubin
- This is because unconjugated bilirubin is bound to albumin and thus does not get filtered
through the glomerulus
When things go wrong…
- If conjugated bilirubin does not get excreted into the bile canaliculi, they get shunted into the
blood plasma (serum)
- This then causes conjugated bilirubin to be found in blood plasma (serum)
- This conjugated bilirubin can thus enter the kidneys and be excreted in the urine as well
2.) ↑ conjugated bilirubin in blood plasma and urine:
- This may be due to obstructive liver disease (thus conjugated bilirubin is shunted back into the
blood)
- This would also occur in specific rare inherited syndromes
Rotor’s Syndrome
Dubin-Johnson Syndrome
Note: there is an exception when checking the urine for conjugated bilirubin. In the case of prolonged
obstructive jaundice (i.e. causing conjugated hyperbilirubinemia), the conjugated bilirubin does
something weird – it binds to albumin! This is known as delta-bilirubin. This is thus not able to be
excreted via the urine. Thus in this case we would expect to find that there is hyperbilirubinemia but no
bilirubinuria.
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