Alanine transaminase

Alanine transaminase or ALT is a transaminase enzyme (EC 2.6.1.2). It is also called serum glutamic pyruvic transaminase (SGPT) or alanine aminotransferase (ALAT).

ALT is found in serum and in various bodily tissues, but is most commonly associated with the liver. It catalyzes the two parts of the alanine cycle.

Function

It catalyzes the transfer of an amino group from alanine to a-ketoglutarate, the products of this reversible transamination reaction being pyruvate and glutamate.

glutamate + pyruvate ⇌ α-ketoglutarate + alanine

Clinical significance

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 normal range values, most show between 5-60 U/L as being normal. Alanine transaminase shows a marked diurnal variation.

Elevated levels

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. 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.^[1]

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, anti-inflammatory drugs, antibiotics, cholesterol medications, and anti-convulsants. Consider advanced schizophrenia.

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.^[2]

See also

• Aspartate transaminase
• Liver function tests

References

External links

• MeSH Alanine+transaminase
• ALT: MedlinePlus Medical Encyclopedia