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Liver Function Tests

The liver is located in the upper right corner of the abdomen, and it plays a variety of important roles in the body: It stores fuel gleaned from sugars, makes needed proteins, and helps remove poisons and toxins. The liver also makes bile, a substance that helps in digestion.

Liver function tests are a group of blood tests that doctors order when they want to find out whether the liver is functioning as it should, and whether there's been any kind of damage to the liver. These tests can help a doctor diagnose viral infections (like mononucleosis or viral hepatitis) or any sort of liver damage from other health problems.

Sometimes liver function tests are referred to as a liver panel and they typically measure: alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), albumin, total protein, and total and direct bilirubin.

The Liver Function Tests
Alanine Transaminase (ALT)

Alanine transaminase is an enzyme that plays a role in processing proteins, and it's found in the liver, heart, muscles, and kidneys. When the liver is injured or inflamed, levels of ALT in the blood usually rise.

Aspartate Transaminase (AST)

Aspartate transaminase is an enzyme that plays a role in metabolism, the process that converts the fuel from food into energy the body needs. If the liver is injured in any way, AST is released into the bloodstream.

Alkaline Phosphatase (ALP)

Alkaline phosphatase is an enzyme in the liver. Kids and teens normally have higher levels of ALP than adults, even when they're healthy. But ALP levels also tend to be higher when kids have viral infections.

Albumin and Total Protein

The levels of albumin (a type of protein the body makes) and total protein show how well the liver is making proteins that the body needs to fight infections, carry oxygen throughout the body, and perform other functions. Sometimes when there's a problem with the liver, it can't make proteins as well, so the levels of total protein and albumin are lower.

Total and Direct Bilirubin

Bilirubin is produced by the normal breakdown of red blood cells. It's the substance that gives bile its yellow-green color. Normally, bilirubin passes through the liver and is eventually excreted through the body. But if that's not happening as it should because of a liver disease or other health problem, bilirubin levels can rise. When high bilirubin levels accumulate in the blood, the skin can take on the yellow discoloration known as jaundice.

Reviewed by: Frederick A. Meier, MD, and Neil Izenberg, MD