ALT (and all transaminases) require the coenzyme pyridoxal phosphate, which is converted into pyridoxamine in the first phase of the reaction, when an amino acid is converted into a keto acid.
It is commonly measured clinically as a part of a diagnostic evaluation of hepatocellular injury, to determine liver health. When used in diagnostics, it is almost always measured in international units/liter (U/L). While sources vary on specific reference range values for patients, 10-40 U/L is the standard reference range for experimental studies. Alanine transaminase shows a marked diurnal variation.
Test results should always be interpreted using the reference range from the laboratory that produced the result. However typical reference intervals for ALT are:
Significantly elevated levels of ALT (SGPT) often suggest the existence of other medical problems such as viral hepatitis, diabetes, congestive heart failure, liver damage, bile duct problems, infectious mononucleosis, or myopathy. For this reason, ALT is commonly used as a way of screening for liver problems. Elevated ALT may also be caused by dietary choline deficiency. However, elevated levels of ALT do not automatically mean that medical problems exist. Fluctuation of ALT levels is normal over the course of the day, and ALT levels can also increase in response to strenuous physical exercise.
When elevated ALT levels are found in the blood, the possible underlying causes can be further narrowed down by measuring other enzymes. For example, elevated ALT levels due to liver-cell damage can be distinguished from biliary duct problems by measuring alkaline phosphatase. Also, myopathy-related ALT levels can be ruled out by measuring creatine kinase enzymes. Many drugs may elevate ALT levels, including Zileuton, omega-3-acid ethyl esters (Lovaza), anti-inflammatory drugs, antibiotics, cholesterol medications, some antipsychotics such as Risperidone, and anti-convulsants.
For years, the American Red Cross used ALT testing as part of the battery of tests to ensure the safety of its blood supply by deferring donors with elevated ALT levels. The intent was to identify donors potentially infected with Hepatitis C because there was no specific test for that disease at the time. Prior to July 1992, widespread blood donation testing in the USA for Hepatitis C was not carried out by major blood banks. With the introduction of second-generation ELISA antibody tests for Hepatitis C, the Red Cross changed the ALT policy. As of July 2003[update], donors previously disqualified for elevated ALT levels and no other reason may be reinstated as donors by contacting the donor counseling department of their regional Red Cross organization.
^ abWang, CS; Chang, Ting-Tsung; Yao, Wei-Jen; Wang, Shan-Tair; Chou, Pesus (2012). "Impact of increasing alanine aminotransferase levels within normal range on incident diabetes". J Formos Med Assoc111 (4): 201–8. doi:10.1016/j.jfma.2011.04.004. PMID22526208.
^Ghouri, N; Preiss, David; Sattar, Naveed (2010). "Liver enzymes, nonalcoholic fatty liver disease, and incident cardiovascular disease: a narrative review and clinical perspective of prospective data". Hepatology52 (3): 1156–61. doi:10.1002/hep.23789. PMID20658466.