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Simplified Disease Activity Index (SDAI) for Rheumatoid Arthritis

The SDAI is the sum of 28-joint tender and swollen counts, patient and evaluator global assessments (0–10) and CRP in mg/dL. Remission ≤3.3, low ≤11, moderate ≤26, high >26.

  • Tender joint count (28 joints) (joints)
  • Swollen joint count (28 joints) (joints)
  • Patient global assessment of disease activity (0–10)
  • Evaluator (physician) global assessment of disease activity (0–10)
  • C-reactive protein (mg/L or mg/dL)
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Interpretation

ResultMeaning
≤ 3.3Remission
> 3.3–11Low
> 11–26Moderate
> 26High

Formula

SDAI = TJC28 + SJC28 + patient global (0–10) + evaluator global (0–10) + CRP (mg/dL). Enter CRP in mg/L or mg/dL; it is converted to mg/dL (mg/L ÷ 10).

Clinical pearls

  • CRP enters the SDAI in mg/dL: a CRP of 20 mg/L adds 2 points, not 20.
  • SDAI ≤3.3 is an ACR/EULAR-endorsed definition of remission, stricter than DAS28 <2.6.

Examples

sdai tjc 4 sjc 4 patient global 5 md global 4 crp 20 mg/Lsimplified disease activity index: 20 tender, 10 swollen, globals 8 and 7, CRP 5 mg/dL

FAQ

What SDAI score is remission?

An SDAI of 3.3 or less is remission; above 3.3 to 11 is low, above 11 to 26 moderate and above 26 high disease activity.

What units is CRP in for the SDAI?

mg/dL. Divide a CRP in mg/L by 10 before adding it (this calculator converts automatically).

Evidence

  1. Smolen JS et al. A simplified disease activity index for rheumatoid arthritis for use in clinical practice. Rheumatology (Oxford) 2003;42:244–57.
  2. Aletaha D, Smolen J. The SDAI and the CDAI: a review of their usefulness and validity in rheumatoid arthritis. Clin Exp Rheumatol 2005;23(5 Suppl 39):S100–8.

General & Anthropometrics · Reviewed 2026-10-14 · Methodology