What type of sample is typically used for a liver function test?

The most common type of sample used for liver function tests is serum. Serum is the liquid portion of blood that remains after coagulation and is free of cells, allowing for the analysis of various biochemical substances. In liver function tests, serum is preferred because it contains enzyme levels, proteins, and metabolites that reflect liver health and function. Key liver enzymes such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST), along with other parameters like bilirubin and alkaline phosphatase, are typically measured in serum.

Using serum also minimizes the impact of clotting factors, which can interfere with certain tests that assess liver function. Since liver function tests aim to evaluate enzyme levels and substances produced or cleared by the liver, serum provides a clear view of these metrics, making it the gold standard for this type of testing.

Whole blood, which still contains cells and clotting factors, may not provide accurate results for the liver function tests focused on biochemical analysis. Plasma, while also a liquid component of blood, can have different characteristics depending on the anticoagulants used during collection, which can affect certain measurements. Urine is unrelated to liver function tests since it is more indicative of renal function rather than hepatic function.