R = (SGPT value ÷ SGPT upper limit of normal [ULN]) ÷ (alkaline phosphatase value ÷ alkaline phosphatase ULN )

An R ratio greater than 5 suggests hepatocellular injury, less than 2 suggests cholestatic injury, and 2-5 indicates a mixed pattern.

Facts

1. Liver  panel includes measurement of serum SGPT, SGOT, alkaline phosphatase, and bilirubin. They are indirect markers of hepatobiliary disease or liver injury; they are not "liver function tests."
2. True tests of liver function include prothrombin time and others that are not commonly performed, such as measurement of hepatic substrates that are cleared by hepatic uptake or metabolism.
3. Hepatocellular disease is typically defined as a disproportionate elevation of the SGOT and SGPT levels compared with alkaline phosphatase levels, whereas cholestatic disease is signaled by a disproportionate elevation of the alkaline phosphatase level compared with SGOT and SGPT levels.
4. Because SGPT is present primarily in the liver, it is a more specific marker of hepatocellular injury than SGOT which is present in the liver as well as other organs, including cardiac muscle, skeletal muscle, kidney, and brain.
5. An increase in SGOT without an elevation in SGPT is suggestive of cardiac or muscle disease.
6. In isolated alkaline phosphatase elevation cholestatic injury can be confirmed by measurement of the serum gamma-glutamyltransferase (GGT) level or fractionation of alkaline phosphatase isoenzymes to differentiate liver alkaline phosphatase from nonliver sources.
7. GGT should not be used as a screening test for underlying liver disease in the absence of abnormal liver chemistries.
8. An elevated serum conjugated bilirubin level implies hepatocellular disease or biliary obstruction.
9. Previous guidelines have recommended basing clinical decisions to evaluate abnormal aminotransferase levels on multiples of the ULN (eg, 3X ULN) without specifically defining the cutoff level of ALT or AST.
10. A normal SGPT level in prospectively studied populations without identifiable risk factors for liver disease ranges from 29 to 33 IU/L for males and from 19 to 25 IU/L for females. Levels above this range should trigger an assessment.
11. A normal SGPT level may not exclude significant liver disease; significant liver disease may occur in the presence of "normal" values on liver chemistry tests. 
12. If SGPT is <5X ULN, assess for hepatitis B and C, alcoholic liver disease, and NAFLD
13. SGPT >15X ULN or > 10,000 IU/L, test for paracetamol toxicity, viral hepatitis and ischemic hepatopathy (shock liver).
14. SGOT / SGPT > 3 increases the likelihood of alcoholic liver disease. [Source Medscape GI]