Calc Function

    • Calcs that help predict probability of a diseaseDiagnosis
    • Subcategory of 'Diagnosis' designed to be very sensitiveRule Out
    • Disease is diagnosed: prognosticate to guide treatmentPrognosis
    • Numerical inputs and outputsFormula
    • Med treatment and moreTreatment
    • Suggested protocolsAlgorithm





    Chief Complaint


    Organ System


    Patent Pending

    Simple Disease Activity Index (SDAI) for Rheumatoid Arthritis

    Determines severity of rheumatoid arthritis using clinical and laboratory data.
    When to Use
    Why Use
    • All patients with rheumatoid arthritis.
    • Reassessing patients after starting a new medication for RA.
    • Assessment of disease activity in rheumatoid arthritis (RA) should be viewed as a dynamic, on-going process; many experts recommend assessing it at every patient visit.
    • Early treatment is important for optimal RA outcomes, and the SDAI can help give a gestalt view of a patient's disease severity and activity.
    • The Clinical Disease Activity Index (CDAI) provides similar information and correlates well but without the need for laboratory data (CRP).
    • The Simplidied Disease Activity Index (SDAI) provides an excellent overview of a patient's disease severity (it correlates closely with the CDAI which does not require laboratory data) and the DAS-28.
    • The SDAI can also help guide therapy based on severity of disease.


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    Next Steps
    Creator Insights

    Critical Actions

    Patients with high activity scores should receive early and aggressive RA medications with close follow-up, as attaining low activity or remission-level scores may prevent disease progression and disability.


    SDAI = Tender Joint Count + Swollen Joint Count + CRP + Patient Global Activity + Provider Global Activity

    Facts & Figures

    SDAI Score Range Disease Severity
    ≤ 3.3 Remission
    > 3.3 - 11.0 Low
    > 11.0 - 26.0 Moderate
    > 26.0 High
    Dr. Josef Smolen

    About the Creator

    Josef Smolen, MD, is a professor of internal medicine and chairman of the Division of Rheumatology at the Medical University of Vienna. Previously, he was president of the European League Against Rheumatism (EULAR), of the Austrian Society of Rheumatology and of the Austrian Society of Immunology. Dr. Smolen focuses on pathogenetic and outcomes research in rheumatological disease.

    To view Dr. Josef Smolen's publications, visit PubMed