Calculators · Rheumatology · Score

SDAI (Simplified Disease Activity Index)

Also called SDAI, simplified disease activity index RA

Rheumatoid arthritis activity: joint counts + global assessments + CRP (mg/dL).

0–10
0–10

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Formula and scoring

SDAI = TJC28 + SJC28 + patient global (0–10) + evaluator global (0–10) + CRP (mg/dL).

Exam and ward pearls

  • SDAI remission (≤3.3) is a stricter target than DAS28 <2.6; CRP contributes only about 5% of SDAI (Aletaha 2005).

When not to rely on it

  • CRP goes in mg/dL; 10 mg/L = 1 mg/dL. Using mg/L inflates the score tenfold for CRP.

Source

  1. Aletaha D, Smolen J. The Simplified Disease Activity Index (SDAI) and the Clinical Disease Activity Index (CDAI): a review of their usefulness and validity in rheumatoid arthritis. Clin Exp Rheumatol. 2005;23(5 Suppl 39):S100-8. PMID 16273793
  2. Aletaha D, Nell VP, Stamm T, et al. Acute phase reactants add little to composite disease activity indices for rheumatoid arthritis: validation of a clinical activity score. Arthritis Res Ther. 2005;7(4):R796-806. doi:10.1186/ar1740 · PMID 15987481
  3. England BR, Tiong BK, Bergman MJ, et al. 2019 Update of the American College of Rheumatology recommended rheumatoid arthritis disease activity measures. Arthritis Care Res (Hoboken). 2019;71(12):1540-55. doi:10.1002/acr.24042 · PMID 31709779

Formula and cut-offs checked against these sources on 8 Nov 2026. Educational tool for clinicians; it does not replace clinical judgement.

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