Allergy and Immunology

SULF-FAST calculator

Enter the published formula inputs below to calculate and interpret this score.

Clinical inputs

Time since the reaction

Five years or less is 2 points. Footnote a says unknown time is included, so unknown also scores 2 points.

Anaphylaxis or angioedema

Severe cutaneous adverse reaction

Anaphylaxis or angioedema and a severe cutaneous adverse reaction share one row of 2 points. Both together still add 2 points. Severe delayed rash with mucosal involvement counts. Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS, and acute generalized exanthematous pustulosis are the printed examples.

Treatment required for the reaction

Treatment required is 1 point. Footnote a includes unknown, so unknown treatment is also 1 point.

Result

4 fields remaining

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Primary source

Waldron JL et al. Development and Validation of a Sulfa Antibiotic Allergy Clinical Decision Rule. JAMA Netw Open. PMID: 37273210. The main text adapts the penicillin rule as SULF-FAST and says a score below 3 carried a low allergy risk (below 5% in the Australian cohort) while a score of 3 or more had a higher allergy risk (above 20% in the Australian cohort). Supplement 1 eMethods says the total score used the scoring algorithm in the eFigure. That eFigure prints 2 points for five years or less since the reaction, 2 points for anaphylaxis or angioedema or a severe cutaneous adverse reaction, and 1 point for treatment required. Footnote a, Includes unknown, is printed on the five-year row and on the treatment row. Footnote b lists Stevens-Johnson syndrome, toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms, and acute generalized exanthematous pustulosis, and says a severe delayed rash with mucosal involvement counts as a severe cutaneous adverse reaction. Anaphylaxis or angioedema and a severe cutaneous adverse reaction are one 2-point row, so both findings still add 2 points. The penicillin interpretation panel in the same figure (very low, low, moderate, and high penicillin test-risk percentages) is not the sulfa cutoff. Acute interstitial nephritis, drug-induced liver injury, serum sickness, and isolated drug fever were excluded phenotypes. (2023)

Scope: Adults aged 18 years or older with a reported trimethoprim-sulfamethoxazole allergy when the Supplement 1 eFigure weights are applied and the published sulfa cutoff is below 3 points versus 3 or more points.

Last reviewed 2026-10-17

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Professional use only

For qualified clinicians. Independently verify inputs, calculations, source guidance, and applicability before any clinical action. This calculator does not replace clinical judgment.

Source: Waldron JL et al. Development and Validation of a Sulfa Antibiotic Allergy Clinical Decision Rule. JAMA Netw Open. PMID: 37273210. The main text adapts the penicillin rule as SULF-FAST and says a score below 3 carried a low allergy risk (below 5% in the Australian cohort) while a score of 3 or more had a higher allergy risk (above 20% in the Australian cohort). Supplement 1 eMethods says the total score used the scoring algorithm in the eFigure. That eFigure prints 2 points for five years or less since the reaction, 2 points for anaphylaxis or angioedema or a severe cutaneous adverse reaction, and 1 point for treatment required. Footnote a, Includes unknown, is printed on the five-year row and on the treatment row. Footnote b lists Stevens-Johnson syndrome, toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms, and acute generalized exanthematous pustulosis, and says a severe delayed rash with mucosal involvement counts as a severe cutaneous adverse reaction. Anaphylaxis or angioedema and a severe cutaneous adverse reaction are one 2-point row, so both findings still add 2 points. The penicillin interpretation panel in the same figure (very low, low, moderate, and high penicillin test-risk percentages) is not the sulfa cutoff. Acute interstitial nephritis, drug-induced liver injury, serum sickness, and isolated drug fever were excluded phenotypes. (2023)

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Clinical inputs

Time since the reaction
Anaphylaxis or angioedema
Severe cutaneous adverse reaction
Treatment required for the reaction

Primary source

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