What is a liver function test?

A liver function test, also called an LFT, is a blood test that measures enzymes and proteins in the blood. Enzyme tests show the extent of damage to a liver, while proteins show how well a liver is performing. An LFT is a diagnostic tool used to detect whether a person’s liver is damaged, and can also be a screening tool for measuring the severity and type of liver disease.

Liver function is measured with a series of blood tests, called a panel. In a standard liver panel, liver enzyme tests measure levels of alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and gamma-glutamyl transpeptidase (GGT). Increased levels of ALT and AST can be a sign of liver damage, while increased levels of ALP and GGT can be a sign of bile duct or liver damage.

Liver protein tests measure total protein, which consists of measuring levels of globulin, prothrombin and albumin; low levels of these proteins in a person’s blood can indicate liver damage. Globulin aids the immune system with fighting infections, prothrombin aids in blood clotting, and albumin levels show whether the liver is producing a normal level of proteins.

A liver panel will also measure bilirubin levels in a person’s body to determine the severity of liver damage. During advanced stages of liver damage, bilirubin can leak out of the liver and cause jaundice, turning the urine dark and eyes yellow.

Before an LFT, a physician will advise their patient not to consume certain foods or drinks that could potentially affect the results. These include over-the-counter and herbal supplements. The results of an LFT can vary depending on factors such as age and gender.

Additional information may be found at these websites:

http://www.nlm.nih.gov/medlineplus/ency/article/003436.htm

http://www.mayoclinic.org/tests-procedures/liver-function-tests/basics/definition/prc-20012602

http://www.liverfoundation.org/abouttheliver/info/liverfunctiontests/