Enter the results
The default upper limits are those used throughout this site. Change them to match the ranges printed on your own laboratory report.
How the R-factor works
Comparing a raw ALT with a raw ALP is meaningless, because the two tests have different reference ranges. The R-factor fixes that by expressing each as a multiple of its own upper limit of normal before dividing:
R = (ALT ÷ ULN of ALT) ÷ (ALP ÷ ULN of ALP)
| R-factor | Pattern | What to think about |
|---|---|---|
| ≥ 5 | Hepatocellular | Viral hepatitis, drugs and paracetamol, alcohol, ischaemic injury, autoimmune hepatitis, Wilson disease |
| 2–5 | Mixed | Many drug reactions; cholangitis inflaming liver cells; overlapping disease |
| ≤ 2 | Cholestatic | Bile duct stones, tumours and strictures; drug cholestasis; PBC and PSC |
Two worked examples
Example A — hepatocellular
ALT 400 (upper limit 41) = 9.76×. ALP 150 (upper limit 105) = 1.43×. R = 9.76 ÷ 1.43 = 6.8. That is hepatocellular: think hepatitis, drugs or ischaemia, and send a viral screen and a paracetamol level.
Example B — cholestatic
ALT 80 (upper limit 41) = 1.95×. ALP 650 (upper limit 105) = 6.19×. R = 1.95 ÷ 6.19 = 0.32. That is cholestatic. The bloods tell you bile is not flowing but not where — so the next test is an ultrasound to ask whether the ducts are dilated.
What the R-factor does not do
It classifies a pattern, not a cause, and it is a guide rather than a rule. Real patients mix categories: cholangitis inflames hepatocytes, and many drugs injure both. Repeating the tests over 24 to 72 hours often tells you more than any single R-factor, because the trend reveals a passing stone or a recovering hepatitis. The R-factor is also used formally in assessing drug-induced liver injury, where it is calculated at the first available set of abnormal results.