Liver Function Test Interpretation

The phrase liver function tests compresses several different measurements into one misleading label. ALT and AST mainly report hepatocyte injury: damaged cell membranes leak these enzymes into the blood, but the result does not tell you whether the liver can still perform its essential functions. ALP, GGT and conjugated bilirubin point more toward impaired bile flow or cholestasis. Albumin and INR give information about synthetic reserve, although albumin also falls with inflammation, nephrotic syndrome and malnutrition, and INR can be altered by causes other than liver failure. A useful reading sequence is: identify the dominant pattern, assess synthetic reserve, fractionate bilirubin, and then search for the cause. The R ratio makes the pattern more reproducible: R = (ALT ÷ ALT ULN) ÷ (ALP ÷ ALP ULN). Calculate it from the presenting bloodwork because the pattern may change as an illness evolves. An R value above 5 is hepatocellular, below 2 is cholestatic, and 2–5 is mixed. Do not let the printed laboratory interval end the assessment. Canadian laboratories establish their own reference ranges, and a result labelled normal may still...