Calculate modified Maddrey discriminant function from PT prolongation and bilirubin without turning a score into a treatment directive.
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Adjacent Calculators
- International Normalized Ratio Calculator — Calculate INR separately when clinically appropriate; classic Maddrey DF requires patient and control PT in seconds, so INR must not be substituted into its formula.
- AUDIT-C Alcohol Screening Calculator — Screen alcohol-use patterns separately; AUDIT-C does not diagnose alcohol-associated hepatitis, calculate Maddrey DF, or determine treatment.
Modified Maddrey Discriminant Function Formula
The modified Maddrey discriminant function, often shortened to modified DF or mDF, combines prothrombin-time prolongation with total bilirubin for severity context in adults with alcohol-associated hepatitis:
Patient PT and control PT must both be entered in seconds. Bilirubin must be expressed in mg/dL when the equation is applied. If bilirubin is entered in µmol/L, the calculator converts it before calculating the score:
The output has no unit. It is a numerical score derived from two laboratory domains: the difference between the patient’s PT and a matched laboratory control PT, plus total bilirubin.
Modified Maddrey DF Variables
| Variable | What to Enter | Required Unit |
|---|---|---|
| Patient PT | The patient’s measured prothrombin time from the relevant laboratory panel. | Seconds |
| Control PT | The matched control value for the laboratory method used to report the patient’s PT. | Seconds |
| Total bilirubin | The patient’s total bilirubin from the corresponding clinical assessment. | mg/dL in the equation; µmol/L is converted by the calculator |
Why the Matched Control PT Matters
The equation does not use patient PT by itself. It uses PT prolongation, calculated as patient PT minus control PT. Control values can differ among laboratories and thromboplastin reagents, so a generic number copied from another source can change the result. Use the control PT supplied for the same laboratory method whenever it is available; do not substitute a personal historical PT or the midpoint of a reference range without laboratory confirmation.
This calculator conservatively rejects patient PT below control PT. A negative prolongation would reduce the score mathematically, but it more often signals that the two values, units, or laboratory contexts should be checked before using a prolongation-based clinical model. This validation rule is a data-quality safeguard, not a diagnosis.
What Is the Maddrey Score?
The Maddrey discriminant function originated in a 1978 clinical study of alcohol-associated hepatitis. Prothrombin-time prolongation and serum bilirubin were identified as important variables in the original discriminant analysis. A later multicenter trial used the modified equation shown above, including the 4.6 coefficient and a value above 32 as a study enrollment criterion.
That history explains why 32 is still widely recognized on the modified DF scale. It is a historical study cutoff, not a universal diagnosis and not a stand-alone treatment instruction. The score can be calculated only after the relevant clinical and laboratory information is known; it cannot determine whether alcohol-associated hepatitis is present.
Modified DF and Current Severity Assessment
The 2024 American College of Gastroenterology guideline describes modified DF as the historical index used in alcohol-associated hepatitis. The same guideline identifies MELD as the most accurate score for current severity stratification and uses MELD above 20 to define severe alcohol-associated hepatitis. Modified DF must not substitute for that current clinician-led severity assessment.
The models are not numerically interchangeable. Modified DF uses PT prolongation and bilirubin, while MELD uses different inputs. A modified DF value cannot be converted into MELD with a simple formula.
How to Calculate the Modified Maddrey DF
- Confirm that patient PT and the matched control PT are both in seconds.
- Subtract control PT from patient PT to find PT prolongation.
- Use total bilirubin in mg/dL. If it is reported in µmol/L, divide by 17.1.
- Multiply PT prolongation by 4.6.
- Add total bilirubin in mg/dL.
- Report the resulting modified DF and its position relative to the historical value of 32.
- Interpret it only within the complete clinician-led evaluation.
Worked Maddrey Score Example
Assume the following values for an educational example:
- Patient PT: 18 seconds
- Matched control PT: 12 seconds
- Total bilirubin: 10 mg/dL
First calculate PT prolongation:
Then apply the modified DF equation:
The result is 37.6, which is above 32 on the historical study scale. That description reports the arithmetic position only. It does not establish the diagnosis, estimate an individual’s mortality, or prescribe treatment.
Example With Bilirubin in µmol/L
Suppose patient PT is 16 seconds, control PT is 12 seconds, and total bilirubin is 232.56 µmol/L. Convert bilirubin first:
Now calculate the score:
This result equals the historical value of 32. The example also shows why unit conversion must occur before bilirubin is added to the PT term.
How to Interpret the Result
The calculator reports one of three neutral positions: below 32, equal to 32, or above 32. A result near 32 is not biologically discontinuous from a nearby value on the other side. Laboratory variation and the selected control PT can move a borderline calculation.
Modified DF also omits several clinical issues that can materially affect assessment, including infection, acute kidney injury, active bleeding, encephalopathy, diagnostic uncertainty, and contraindications. It should be reviewed alongside current severity measures and the full clinical presentation.
Why INR Cannot Replace PT
INR standardizes PT for certain coagulation uses, but it is not the same input as PT prolongation in the modified DF equation. Do not place an INR value into either PT field. If only INR is available, the information needed to reproduce this equation has not been supplied. An INR-based model or calculator answers a different question.
Common Input Mistakes
- Using INR instead of patient PT in seconds.
- Entering the upper end of a PT reference range when a matched control PT is required.
- Mixing patient PT and control PT from different laboratories or reagent systems.
- Entering bilirubin in µmol/L while selecting mg/dL, which makes the bilirubin contribution about 17 times too large.
- Using direct bilirubin instead of total bilirubin.
- Reversing patient PT and control PT.
- Trying to reverse-solve a PT value for a target score of 32.
- Treating a historical cutoff as a diagnosis, treatment recommendation, or personal outcome estimate.
Clinical Scope and Limitations
This calculator is limited to the forward modified DF equation. It does not reverse-solve a PT target, calculate MELD, establish alcohol-associated hepatitis, or determine eligibility for medication. The arithmetic should be reviewed by a clinician who can confirm the diagnosis, source the correct control PT, evaluate competing causes of liver injury, and apply current guidance.
Frequently Asked Questions
Is Maddrey DF the Same as MELD?
No. They are separate models with different inputs, formulas, and clinical histories. Current 2024 ACG guidance recommends MELD above 20 for severity stratification in alcohol-associated hepatitis, while describing modified DF as a historical index.
Why Does This Calculator Not Solve for the PT Needed to Reach 32?
The published equation is a forward severity model based on observed values, not a target-setting equation. Reverse-solving PT could imply that a laboratory target determines care, which is not a validated use. The calculator therefore accepts measured inputs and reports only the resulting score.
Can a Modified DF Result Diagnose Alcohol-Associated Hepatitis?
No. The diagnosis requires clinical evaluation and exclusion of competing explanations. Modified DF assumes that the relevant clinical context has already been established; it does not establish the cause of abnormal bilirubin or coagulation results.
Why Can the Control PT Change the Score?
The control value is subtracted directly from patient PT, and the difference is then multiplied by 4.6. A one-second change in control PT changes the calculated score by 4.6 points when all other inputs stay the same. That is why the matched laboratory control is important.
Medical note: This calculator reproduces a historical clinical equation for educational and clinician-support purposes. It is not a stand-alone treatment recommendation or individual mortality prediction.
Primary and current sources: Maddrey et al., original discriminant-function study, Carithers et al., modified DF multicenter trial, and 2024 ACG Clinical Guideline: Alcohol-Associated Liver Disease.
