When we order liver function tests (LFTs) we normally get ALT / GGT / ALP / bilirubin / total protein / albumin. But are these true liver function tests? Should we add anything?
Well, ALT (alanine transaminase), AST (aspartate transaminase) are enzymes present in hepatocytes, GGT (gamma-glutamyl transpeptidase) in the hepatocytic membrane. If they are elevated they indicate acute hepatocyte injury, but they don’t give use any information about the actual function of the liver.
If you recall from medical school what the functions of the liver are, it’s easy to remember what tests to request:
– protein synthesis – low albumin and total protein
– production of non-endothelial coagulation factors (factors II, V, VII, IX, X, XI, XIII) – PT, INR will be elevated
Protein C and S are also synthesized in the liver, thus chronic liver disease is a prothrombotic state, despite having elevated INR and PT (and patients can get portal vein thrombosis, pulmonary embolism etc.).
Although not a direct function of the liver, thrombocytopaenia is a feature of chronic liver disease, due to a multitude of factors that include splenic sequestration and bone marrow suppression.
– bilirubin clearance – bilirubin resulted from haem breakdown is conjugated in hepatocytes and excreted in bile; elevated unconjugated (indirect) haemoglobin can be a marker of liver disease (can occur in haemolysis as well), while elevated conjugated (direct) haemoglobin is a marker of obstruction of the biliary tree
– gluconeogenesis / glycogenolysis / glycogenogenesis – hypoglycaemia is a marker of severe liver disease; patients with chronic liver disease have very poor glycogen stores and therefore their hypoglycaemic episodes should not be treated with glucagon as they have no glycogen to metabolize to glucose
– cholesterol and triglycerides synthesis
– conversion of ammonia to urea – elevated ammonia levels are markers of severe liver disease and one of the causes of hepatic encephalopathy