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Aminotransferase – Function, Values and Diagnosis

Aminotransferases are enzymes that play a key role in metabolism and serve as laboratory markers for assessing liver and heart health.

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Things worth knowing about "Aminotransferase"

Aminotransferases are enzymes that play a key role in metabolism and serve as laboratory markers for assessing liver and heart health.

What Are Aminotransferases?

Aminotransferases (also known as transaminases) are enzymes found in various tissues throughout the human body, particularly in the liver, heart muscle, skeletal muscle, and kidneys. They catalyze reactions in which amino groups are transferred from one molecule to another – a central step in amino acid and energy metabolism.

In clinical practice, two aminotransferases are of particular importance:

ALT (Alanine Aminotransferase), previously known as GPT (Glutamate Pyruvate Transaminase) – found mainly in the liver
AST (Aspartate Aminotransferase), previously known as GOT (Glutamate Oxaloacetate Transaminase) – found in the liver, heart muscle, and skeletal muscle

Biological Function

Aminotransferases play a central role in amino acid metabolism. They enable the transfer of amino groups to keto acids, resulting in the formation of new amino acids. This process, known as transamination, is essential for amino acid biosynthesis, protein breakdown, and the provision of energy substrates in the body.

Clinical Significance as Laboratory Values

Under normal conditions, aminotransferases are found predominantly within cells. When cells are damaged – for example due to inflammation, disease, or injury – these enzymes are released into the bloodstream. Elevated aminotransferase levels in the blood are therefore an important indicator of tissue damage.

Reference Values

Reference ranges may vary slightly between laboratories, but typical values are:

ALT: up to approximately 35–45 U/L (units per liter), depending on sex
AST: up to approximately 35–40 U/L

Elevated Values – Possible Causes

Elevated aminotransferase levels may indicate a variety of conditions:

Liver diseases: hepatitis (viral, alcoholic, autoimmune), fatty liver disease (NAFLD/NASH), liver cirrhosis, liver cancer
Heart conditions: myocardial infarction (especially elevated AST)
Muscle disorders: myopathies, intense physical exercise
Medications: certain drugs can stress the liver and cause elevated values (e.g., statins, high-dose paracetamol/acetaminophen)
Thyroid disorders and other metabolic conditions

Diagnosis and Laboratory Testing

Aminotransferase levels are measured from a simple blood sample. This test is part of a routine liver function panel and is commonly ordered during health check-ups, to monitor drug therapy, or when liver disease is suspected.

To help differentiate between conditions, the ratio of AST to ALT – known as the De Ritis ratio – is used. A value above 2 often suggests alcoholic liver disease, while a value below 1 is more indicative of viral hepatitis or non-alcoholic fatty liver disease.

Treatment for Elevated Values

Elevated aminotransferase levels are not a disease in themselves but a sign of an underlying condition. Treatment is therefore always directed at the root cause:

Alcoholic liver disease: abstinence from alcohol
Viral hepatitis: antiviral therapy
Fatty liver disease: weight reduction, dietary changes, increased physical activity
Drug-induced elevation: adjustment or discontinuation of the causative medication (only under medical supervision)

Important: elevated aminotransferase levels should always be evaluated by a physician, even in the absence of symptoms.

References

Longo DL et al. (eds.) – Harrison's Principles of Internal Medicine, 21st Edition, McGraw-Hill Education (2022)
Kwo PY, Cohen SM, Lim JK – ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries. American Journal of Gastroenterology, 2017; 112(1):18–35. PubMed PMID: 27995906
World Health Organization (WHO) – Laboratory Manual for Biochemical Testing, WHO Press (2020)

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