Alanine aminotransferase

Alanine aminotransferase

glutamic-pyruvate transaminase
Identifiers
Symbol GPT
Entrez HUGO OMIM RefSeq UniProt EC number Locus q24.2-qter
Alanine transaminase
Identifiers
EC number CAS number IntEnz BRENDA ExPASy KEGG MetaCyc metabolic pathway
PRIAM PDB structures PDBsum
Gene Ontology EGO

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

ALT is found in plasma 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 L-alanine to α-ketoglutarate, the products of this reversible transamination reaction being pyruvate and L-glutamate.

L-glutamate + pyruvate α-ketoglutarate + L-alanine


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.

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).[1][2] While sources vary on specific reference range values for patients, 10-40 U/L is the standard reference range for experimental studies.[1] Alanine transaminase shows a marked diurnal variation.

Elevated levels

Test results should always be interpreted using the reference range from the laboratory that produced the result. However typical reference intervals for ALT are:

Patient type Reference ranges[3]
Female ≤ 34 IU/L
Male ≤ 45 IU/L

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.[4]

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),[5] 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, 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.[6]

See also

References

External links

  • Medical Subject Headings (MeSH)
  • ALT: analyte monograph; The Association for Clinical Biochemistry and Laboratory Medicine
  • Alanine aminotransferase (ALT) at Lab Tests Online