Liver Function Tests Health Article

Definition

Liver function tests, or LFTs, include tests that are routinely measured in all clinical laboratories. LFTs include bilirubin, a compound formed by the breakdown of hemoglobin; ammonia, a breakdown product of protein that is normally converted into urea by the liver before being excreted by the kidneys; proteins that are made by the liver including total protein, albumin, prothrombin, and fibrinogen; cholesterol and triglycerides, which are made and excreted via the liver; and the enzymes alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), and lactate dehydrogenase (LDH). Other liver function tests include serological tests (to demonstrate antibodies) and DNA tests for hepatitis and other viruses; and tests for antimitochondrial and smooth muscle antibodies, transthyretin (prealbumin), protein electrophoresis, bile acids, alpha-fetoprotein, and a constellation of other enzymes that help differentiate necrotic (characterized by death of tissues) versus obstructive liver disease.

Purpose

Liver function tests done individually do not give the physician very much information, but used in combination with a careful history, physical examination, and imaging studies, they contribute to making an accurate diagnosis of the specific liver disorder. Different tests will show abnormalities in response to liver inflammation; liver injury due to drugs, alcohol, toxins, or viruses; liver malfunction due to blockage of the flow of bile; and liver cancers.

Precautions

Blood for LFTs is collected by sticking a needle into a vein. The nurse or phlebotomist performing the procedure must be careful to clean the skin before sticking in the needle.

Bilirubin: Drugs that may cause increased blood levels of total bilirubin include anabolic steroids, antibiotics, antimalarials, ascorbic acid, Diabinese, codeine, diuretics, epinephrine, oral contraceptives, and vitamin A.

Ammonia: Muscular exertion can increase ammonia levels, while cigarette smoking produces significant increases within one hour of inhalation. Drugs that may cause increased levels include alcohol, barbiturates, narcotics, and diuretics. Drugs that may decrease levels include antibiotics, levodopa, lactobacillus, and potassium salts.

ALT: Drugs that may increase ALT levels include acetaminophen, ampicillin, codeine, dicumarol, indomethacin, methotrexate, oral contraceptives, tetracyclines, and verapamil. Previous intramuscular injections may cause elevated levels.

GGT: Drugs that may cause increased GGT levels include alcohol, phenytoin, and phenobarbital. Drugs that may cause decreased levels include oral contraceptives.

LDH: Strenuous activity may raise levels of LDH. Alcohol, anesthetics, aspirin, narcotics, procainamide, and fluoride may also raise levels. Ascorbic acid (vitamin C) can lower levels of LDH.