AST : ALT ratio

• ratio of AST to ALT has been used as a diagnostic aid:
  • AST:ALT ratio of more than 2:1 is characteristic in patients with alcoholic liver disease
    • a raised AST level out of proportion to the ALT level appears to be caused by a differential reduction in hepatic ALT due to deficiency of the cofactor pyridoxine-5-phosphate
    • AST:ALT ratio of more than 2:0 is suggestive of alcoholic liver disease - however this result does not preclude other diagnoses
      • a raised ALT level to more than 500 IU/L suggests a diagnosis other than alcoholic liver disease, even if the AST:ALT ratio is greater than 2:0
        • other blood tests also suggestive of the presence of alcoholic liver disease include raised of serum gamma-glutamyltranspeptidase (GGT) level and mean corpuscular volume
    • in viral viral hepatitis
      • the AST:ALT ratio, which is typically less than 1:0 (particularly true in patients with hepatitis C), can rise to greater values as fibrosis and cirrhosis develop
      • exact mechanism of AST:ALT ratio alteration in progression of liver disease is unclear, and the correlation with and accuracy in predicting degree of fibrosis and presence of cirrhosis are controversial
    • in many forms of acute and chronic liver injury or steatosis (fatty infiltration of the liver), the ratio is less than or equal to 1
      • study of 140 patients with nonalcoholic steatohepatitis (NASH; confirmed by liver biopsy) or alcoholic liver disease found a mean AST/ALT ratio of 0.9 in patients with NASH and 2.6 in patients with alcoholic liver disease (2)
        • within the study population
          • 87 percent of patients with an AST/ALT ratio of 1.3 or less had NASH (87 percent sensitivity, 84 percent specificity)
          • severity of NASH as measured by the degree of fibrosis increased, as did the AST/ALT ratio
          • mean ratio of 1.4 was found in patients with cirrhosis related to NASH
    • Wilson's disease can cause the AST/ALT ratio to exceed 4 (3)

In conclusion

• AST:ALT ratios are suggestive of certain conditions
  • there is significant overlap between AST:ALT ratios in different conditions
  • this ratio cannot be relied on exclusively when making a diagnosis

Reference:

• (1) Gopal DV, Rosen HR. Abnormal findings on liver function tests Interpreting results to narrow the diagnosis and establish a prognosis. Postgraduate Medicine 2000; 107 (2).
• (2) orbi D et al. The ratio of aspartate aminotransferase to alanine aminotransferase: potential value in differentiating nonalcoholic steatohepatitis from alcoholic liver disease. Am J Gastroenterol 1999;94:1018-22.
• (3) Davern TJ, Scharschmidt BF. Biochemical liver tests. In: Feldman M, Friedman LS, Sleisenger MH, eds. Sleisenger & Fordtran's Gastrointestinal and liver disease: pathophysiology, diagnosis, management. 7th ed. Philadelphia: Saunders, 2002:1227-38.