Liver function tests

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A set of biochemical tests related to the liver. It is a misnomer, as the individual tests give only a loose indication of true Liver function and are more markers of liver damage or cholestasis. As the liver is a complex metabolic organ with many functions, it is impossible to exhaustively test metabolic function with a limited set of tests. For this reason, many biochemistry departments avoid calling these tests 'liver function tests', preferring more general, though admittedly vague labels like the 'liver group' of tests.

Contents

Pathophysiology

Providing these limitations are appreciated, these tests can collectively provide useful information about the hepatobiliary system (see below and individual tests). The exact selection of tests that make up the liver group varies from hospital to hospital, but generally includes most of the following:

Tests

Breakdown product of the haem moiety of haemoglobin, myoglobin and cytochromes. Hepatocytes are involved in the degradation and processing of haem into bilirubin.
raised in alcoholic liver disease and in liver damage, but smaller increases can be seen in cholestasis.
Increased in hepatocellular damage, but smaller increases can be seen in cholestasis.
May be bone or liver origin. Disproportionately increased in cholestasis and biliary obstruction.
Disproportionately increased in cholestasis and biliary obstruction. May be raised patients with high alcohol intake.
Rough measure of synthetic function. One of the most abundant circulating plasma proteins. Functions as transport molecule and also contributes to oncotic pressure. Low levels can be associated with non-liver disease (e.g. malnutrition, sepsis, catabolic states)

Other Useful Tests

Raised in cholestasis.
Can be a useful test of liver synthetic function, e.g. deranged clotting following paracetamol overdose is a bad prognostic indicator. Many of the clotting factors have fairly short half-lives (4-24 hours), so any impairment in synthetic function is quickly reflected in deranged clotting. However, in chronic liver disease, prothrombin time may not accurately reflect actual coagulation as the derangements in both pro-thrombotic and anti-thrombotic affect clotting function in a complex way.[1]
Made in the liver. Low levels seen in severe liver disease.

Interpretation

Primary care

See BMJ article.[2]

Online CPD modules on LFTs

References

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