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Test ID: ALT    
Alanine Aminotransferase (ALT) (GPT), Serum

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Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis and monitoring of liver disease associated with hepatic necrosis

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Alanine aminotransferase (ALT) is present primarily in liver cells. In viral hepatitis and other forms of liver disease associated with hepatic necrosis, serum ALT is elevated even before the clinical signs and symptoms of the disease appear. Although serum levels of both aspartate aminotransferase (AST) and ALT become elevated whenever disease processes affect liver cell integrity, ALT is a more liver-specific enzyme. Serum elevations of ALT are rarely observed in conditions other than parenchymal liver disease. Moreover, the elevation of ALT activity persists longer than does AST activity.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Males

> or =1 year: 7-55 U/L

Reference values have not been established for patients who are <12 months of age.

Females

> or =1 year: 7-45 U/L

Reference values have not been established for patients who are <12 months of age.

Interpretation Provides information to assist in interpretation of the test results

Elevated alanine aminotransferase (ALT) values are seen in parenchymal liver diseases characterized by a destruction of hepatocytes. Values are typically at least ten times above the normal range. Levels may reach values as high as one hundred times the upper reference limit, although twenty to fifty-fold elevations are most frequently encountered. In infectious hepatitis and other inflammatory conditions affecting the liver, ALT is characteristically as high as or higher than aspartate aminotransferase (AST), and the ALT/AST ratio, which normally and in other condition is <1, becomes greater than unity. ALT levels are usually elevated before clinical signs and symptoms of disease appear.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Pyridoxal phosphate is a cofactor in the reaction and must be present for optimal enzyme activity.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

Tietz Textbook of Clinical Chemistry. Edited by CA Burtis, ER Ashwood. Philadelphia, WB Saunders Company, 1994