R Factor for Liver Injury
Differentiates cholestatic from hepatocellular liver injury, recommended by ACG guidelines.
Use the first lab values (ALT and ALP) indicating acute liver injury to calculate the R factor.
Advice
R Factor >5 suggests hepatocellular pattern of liver injury.
- Acute viral hepatitis, ischemic liver injury, Budd-Chiari syndrome, autoimmune hepatitis, and Wilson’s disease (in younger patients) should be ruled out as causes.
- Commonly used drugs that can cause this pattern of liver injury include: isoniazid, macrolides, nitrofurantoin, minocycline, anti-epileptics, NSAIDs, green tea extract, and inhaled anesthetics.
R Factor <2 suggests cholestatic pattern of liver injury.
- Pancreatic malignancy, cholangiocarcinoma, primary malignancy of the gallbladder, choledocholithiasis, sepsis, TPN, heart failure, PSC, and PBC should be ruled out as causes.
- Commonly used drugs that can cause this pattern of liver injury include: amoxicillin/clavulanate, trimethoprim/sulfamethoxazole, azathioprine, and anabolic steroids.
R Factor between 2 and 5 suggests a mixed pattern of liver injury.
Management
Recommendations for workup based on R Factor, adapted from Chalasani 2014.
Critical Actions
Though the R Factor does not incorporate coagulopathy (INR) and mental status, these two factors should always be immediately assessed in all cases of acute liver injury to rule out acute liver failure.