Alanine aminotransferase

Introduction

ALT is also known as GPT

Elevated blood values are not specific for one tissue and is not a reliable indicator of liver or muscle damage. ALT is not usually part of routine biochemistry.

ALT (Alanine aminotransferase) is considered to be liver specific in dogs and cats, although small amounts are present in muscle (skeletal and cardiac) and low levels in several body organs. It is not useful in large animals. ALT is found in the cytoplasm of hepatocytes and is released into the blood during changes in cell membrane permeability or necrosis. It’s cytoplasmic location means that a relatively mild insult, for example, hypoxia, may lead to increased serum levels. ALT is not an indicator of hepatic function. The half life is around 1-2 days in the dog and shorter in the cat. Therefore smaller changes are more significant in the cat. In chronic hepatic disease with loss of functional hepatocytes levels may be deceptively low. In acute disease, a rapid decline in levels may be a favourable sign. Research has demonstrated that ALT levels also increase due to increased synthesis and release by regenerating hepatocytes. The magnitude of the rise in ALT does not reflect the nature, severity of the disease, or the prognosis. Persistent elevation of ALT over 6-8 weeks is an indication for further investigation.

Causes of increased ALT activity

Primary Hepatopathies

• Acute and cholestatic liver disease
• Chronic active hepatitis (dog)
• Toxic hepatitis
• Cholangiohepatitis (cat)
• HypoxiaLiver trauma
• Hepatic neoplasia

Secondary hepatopathies

• Hyperthyroidism (cat)
• Hyperadrenocorticism
• Diabetes mellitus
• Glucocorticoid therapy
• Acute pancreatitis
• Hypothyroidism (dog)
• Posthepatic obstructive jaundice

Complementary tests

ALT activity is usually determined in conjunction with other tests of hepatocellular damage or hepatic function specifically ALP, GLDH, AST, GGT, albumin and bile acids.

Authors and References

NationWide Laboratories