R factor
Classifies a liver injury as hepatocellular, cholestatic or mixed, from the ALT and ALP each expressed as a multiple of the upper limit of normal. It is used in drug-induced liver injury, including for choosing the RUCAM scale. Use values from the first abnormal set of results.
Enter ALT and ALP.
How it is worked out
- R = (ALT ÷ ALT upper limit) ÷ (ALP ÷ ALP upper limit)
- New R (nR) uses whichever of ALT or AST is the higher multiple of its upper limit.
| R | Pattern |
|---|---|
| 5 or more | Hepatocellular |
| Above 2 and below 5 | Mixed |
| 2 or less | Cholestatic |
Hy's law
ALT or AST above 3 times the upper limit with bilirubin above 2 times the upper limit, without an initial cholestatic picture (ALP below 2 times the upper limit), and no other explanation. In drug-induced liver injury it predicts a mortality or transplant rate of about 10%.
Notes
- The pattern can change as the injury evolves, so the first set of abnormal results is the one to classify.
- ALP from bone, pregnancy or growth raises it without liver injury. A raised GGT supports a liver source.
- For the full panel of liver scores from one set of results, use the liver blood test panel.
References
Chalasani NP, Maddur H, Russo MW, et al. ACG Clinical Guideline: diagnosis and management of idiosyncratic drug-induced liver injury. Am J Gastroenterol. 2021;116(5):878-898.
European Association for the Study of the Liver. EASL Clinical Practice Guidelines: drug-induced liver injury. J Hepatol. 2019;70(6):1222-1261.