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R Factor for Drug-Induced Liver Injury Pattern

R = (ALT ÷ ALT ULN) ÷ (ALP ÷ ALP ULN). R ≥ 5 indicates a hepatocellular pattern, R ≤ 2 a cholestatic pattern, and R between 2 and 5 a mixed pattern of liver injury (CIOMS/RUCAM; ACG 2021 DILI guideline).

  • ALT (U/L)
  • ALT upper limit of normal (U/L)
  • Alkaline phosphatase (ALP) (U/L)
  • ALP upper limit of normal (U/L)
  • AST (optional, for "new R") (U/L)
  • AST upper limit of normal (U/L)
—

Interpretation

ResultMeaning
≥ 5Hepatocellular
> 2 to < 5Mixed
≤ 2Cholestatic

Formula

R = (ALT ÷ ALT ULN) ÷ (ALP ÷ ALP ULN). New R (nR) uses the higher of ALT or AST (each ÷ its ULN) in the numerator.

Clinical pearls

  • Use the first set of liver tests at presentation; R changes over time as the injury evolves.
  • ULNs default to ALT 40 U/L and ALP 120 U/L if not entered; use your laboratory's reference limits.
  • The pattern selects the RUCAM causality scale (hepatocellular vs cholestatic/mixed) and narrows the differential, but it does not establish that a drug is the cause.

Examples

r factor alt 400 alp 150dili pattern ALT 250 (ULN 35) ALP 300 (ULN 115)is this liver injury hepatocellular or cholestatic? ALT 80, alk phos 360

FAQ

How do you calculate the R factor?

Divide ALT by its upper limit of normal, divide ALP by its upper limit of normal, then divide the first ratio by the second.

What R value means hepatocellular injury?

R ≥ 5 is hepatocellular; R ≤ 2 is cholestatic; values in between are mixed.

Evidence

  1. Bénichou C. Criteria of drug-induced liver disorders. Report of an international consensus meeting. J Hepatol 1990;11:272–6.
  2. Chalasani NP et al. ACG Clinical Guideline: Diagnosis and Management of Idiosyncratic Drug-Induced Liver Injury. Am J Gastroenterol 2021;116:878–98.

Hepatology & GI · Reviewed 2026-10-14 · Methodology