| Alanine transaminase | |||||||||
|---|---|---|---|---|---|---|---|---|---|
 | |||||||||
| Identifiers | |||||||||
| EC no. | 2.6.1.2 | ||||||||
| CAS no. | 9000-86-6 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDBPDBePDBsum | ||||||||
| Gene Ontology | AmiGO /QuickGO | ||||||||
| |||||||||
Alanine transaminase (ALT), also known asalanine aminotransferase (ALT orALAT), formerlyserum glutamate-pyruvate transaminase (GPT) orserum glutamic-pyruvic transaminase (SGPT), is atransaminaseenzyme (EC2.6.1.2) that was first characterized in the mid-1950s by Arthur Karmen and colleagues.[1] ALT is found inplasma and in various body tissues but is most common in theliver. It catalyzes the two parts of thealanine cycle. Serum ALT level, serum AST (aspartate transaminase) level, and their ratio (AST/ALT ratio) are routinely measured clinically asbiomarkers for liver health.[2]
Thehalf-life of ALT in the circulation approximates 47 hours.[3]Aminotransferase is cleared bysinusoidal cells in the liver.[3]
ALT catalyzes the transfer of anamino group fromL-alanine toα-ketoglutarate, the products of this reversibletransamination reaction beingpyruvate andL-glutamate.[4]
ALT (and all aminotransferases) require the coenzymepyridoxal phosphate, which is converted into pyridoxamine in the first phase of the reaction, when an amino acid is converted into a keto acid.[5]
ALT is commonly measured clinically as part ofliver function tests and is a component of theAST/ALT ratio.[6] When used in diagnostics, it is almost always measured in international units/liter (IU/L)[7] orμkat. While sources vary on specific reference range values for patients, 0-40 IU/L is the standard reference range for experimental studies.[6]
Test results should always be interpreted using thereference range from the laboratory that produced the result. However typical reference intervals for ALT are:
| Patient type | Reference ranges[8] |
| Male | ≤ 45 IU/L |
| Female | ≤ 34 IU/L |
Significantly elevated levels of ALT (SGPT) often suggest the existence of other medical problems such as viralhepatitis,diabetes,congestive heart failure, liver damage,bile duct problems,infectious mononucleosis, ormyopathy, so ALT is commonly used as a way of screening for liver problems.[citation needed] Elevated ALT may also be caused by dietarycholine deficiency.[citation needed] 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 they can also increase in response to strenuous physical exercise.[9]
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 tohepatocyte damage can be distinguished from bile duct problems by measuringalkaline phosphatase. Also, myopathy-related elevations in ALT should be suspected when the aspartate transaminase (AST) is greater than ALT; the possibility of muscle disease causing elevations in liver tests can be further explored by measuring muscle enzymes, includingcreatine kinase. Many drugs may elevate ALT levels, includingzileuton,omega−3-acid ethyl esters (Lovaza),[10] anti-inflammatory drugs, antibiotics, cholesterol medications, some antipsychotics such as risperidone, and anticonvulsants.[11]Paracetamol (acetaminophen) may also elevate ALT levels.[12]
For years, theAmerican 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 no specific test for that disease was available at the time. Prior to July 1992, widespread blood donation testing in the US for hepatitis C was not carried out by major blood banks. With the introduction of second-generationELISA antibody tests forhepatitis 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 when they contact the donor-counseling department of their regional Red Cross organization.[13]
In 2000, the American Association for Clinical Chemistry determined that the appropriate terminology for AST and ALT are aspartate aminotransferase and alanine aminotransferase. The term transaminase is outdated and no longer used in liver disease.[14]
Low plasma ALT can be a marker of lowmuscle mass and is associated withfrailty,sarcopenia,disability, as well as increased mortality in the elderly population.[15] In patients withinflammatory bowel disease, low ALT is associated with a more active disease.[16]
Aminotransferase clearance is carried out within the liver by sinusoidal cells. The half-life in the circulation is about 47 hours for ALT, about 17 hours for total AST and, on average, 87 hours for mitochondrial AST.
