How this calculator works
The modified DF uses the difference between patient and laboratory control prothrombin times, plus total bilirubin in mg/dL. This differs from Maddrey's original unmodified formula. A value of at least 32 is a traditional severity threshold in alcohol-associated hepatitis. It does not independently establish that diagnosis or determine whether corticosteroids are appropriate. Use PT in seconds, not INR or activated partial thromboplastin time. The result is an estimate for information only and is not medical advice.
Formula
Modified DF = 4.6 x (patient PT - control PT, in seconds) + total bilirubin (mg/dL). Reverse modes rearrange this linear expression.
Worked example
PT 18 seconds, control 12 seconds and bilirubin 10 mg/dL give 4.6 x 6 + 10 = 37.6. With PT 16, control 12 and bilirubin 8, the result is 26.4.
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Frequently asked questions
Can I substitute INR for PT?
No. This version requires PT in seconds and its matching laboratory control.
Does DF at least 32 mean steroids should be started?
No. Diagnosis, contraindications, infection assessment and specialist judgement are required.
Can DF be negative?
Yes, if patient PT is shorter than control and bilirubin is low. The arithmetic is preserved; interpretation needs context.