Liver Function Tests
Liver Function Tests: PT and INR
Besides its functions in metabolism, the liver makes proteins that are essential to normal blood clotting. True liver function tests check the liver's ability to make these proteins. They include:
- Prothrombin time (PT): A test of the time it takes for a blood sample to clot, under specific conditions in a lab; if low levels of clotting factors are present, the prothrombin time is longer.
- International normalized ratio (INR): Not really a test, but a standardized way for all labs to report PT, so their results can be compared accurately with each other.
PT and INR rise in people with severe liver disease because the liver fails to make normal amounts of certain clotting factors. An elevated PT can have many other causes besides liver disease, however.
PT is often checked together with PTT (partial thromboplastin time), which is not a liver function test. If PT and/or PTT are elevated, a problem with bleeding or clotting may be present.
Liver Function Tests: Albumin
The liver also makes albumin, an essential protein that circulates in blood. Albumin levels are low in people with severe chronic liver disease, because the liver does not make normal amounts of albumin. However, albumin levels also may fall in a variety of medical conditions. A low albumin level is often temporary, so it is not a reliable way to diagnose liver disease.
Liver Function Tests: Bilirubin
Bilirubin is a waste product from the breakdown of red blood cells. The liver processes bilirubin so it can be excreted in stool. Bilirubin flows through the liver's bile ducts, dissolved in bile.
Bilirubin blood levels may be elevated in people with impaired bile flow. This can occur in severe liver disease, gallbladder disease, or other bile system conditions. Very high bilirubin levels cause jaundice, in which the skin and whites of the eyes turn yellow. Bilirubin can be a useful liver function test in people with a known bile flow problem. An elevated bilirubin may also be present in people with a type of anemia, called hemolytic anemia.