This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
Why classify liver injury?
When liver tests come back abnormal, the pattern of the abnormality points to the cause. Damage to the liver cells themselves (hepatocellular injury) releases ALT, while blocked bile flow (cholestasis) raises alkaline phosphatase (ALP). Viral hepatitis, ischemia and many drugs such as acetaminophen overdose cause a hepatocellular pattern; gallstones, tumors and drugs such as amoxicillin-clavulanate often cause a cholestatic or mixed one.
The formula
The R factor compares the two enzymes, each relative to its own upper limit of normal (ULN), so that results from different labs can be compared:
R = (ALT ÷ ULN of ALT) ÷ (ALP ÷ ULN of ALP)
| R | Pattern |
|---|---|
| 5 or more | hepatocellular |
| above 2 and below 5 | mixed |
| 2 or less | cholestatic |
These cut-offs come from an international consensus meeting published in 1990 and are used by the RUCAM method to assess whether a drug caused liver injury, and by drug regulators.
The new R
Some injuries raise AST much more than ALT. The “new R” uses whichever of ALT or AST is higher relative to the upper limit. Enter an AST value to see it; with no AST, it equals the classic R.
Example
With an ALT of 250 U/L (ULN 40) and an ALP of 140 U/L (ULN 120), ALT is 6.25 times normal and ALP 1.17 times normal. R is 6.25 ÷ 1.17 = 5.36: a hepatocellular pattern.
Hy’s law
Hyman Zimmerman observed that drug-induced hepatocellular injury combined with jaundice was fatal in about 10% of cases. Regulators now flag any case with ALT above 3 times normal and total bilirubin above 2 times normal, without a large rise in ALP and without another explanation. The calculator shows a warning when this pattern appears.
Practical notes
- Use the first abnormal results, as the pattern can shift over time.
- Check the ULN printed on your lab report; it differs between labs and sometimes by sex.
- A pattern is a clue, not a diagnosis: imaging, viral serology and the medication history complete the picture.