Autoimmune Disease Activity Calculator

EULAR's standard bands are: below 2.6 is remission, 2.6 up to 3.2 is low disease activity, above 3.2 up to 5.1 is moderate disease activity, and above 5.1 is high disease activity. This calculator uses those same four cutoffs to classify the computed score and flags moderate-or-higher activity as a point to discuss treatment escalation with a rheumatologist.

Both joint counts enter the DAS28-ESR formula through a square root (0.56 x sqrt(TJC28) and 0.28 x sqrt(SJC28)), which grows more slowly as the count rises. Going from 0 to 1 tender joint changes sqrt(TJC28) by a full point, while going from 15 to 16 changes it by only about 0.13 -- so the formula is most sensitive to the first few joints affected and progressively less sensitive as more joints are involved.

Both matter, but they enter differently. ESR is transformed with a natural logarithm (0.70 x ln(ESR)), which compresses the influence of very high values, while the patient VAS enters linearly (0.014 x VAS) with a small fixed coefficient. In practice, that means a change in ESR from, say, 10 to 20 mm/hr moves the score more than the same 10-point rise from 80 to 90 mm/hr, whereas each additional VAS point contributes the same fixed amount regardless of where the VAS started.

Not exactly. The formally documented Clinical Disease Activity Index sums tender and swollen joint counts with SEPARATELY recorded patient and physician global assessments (each on a 0-10 cm scale). This calculator does not collect a physician assessment, so it estimates one from the swollen joint count as a stand-in. Treat the CDAI figure here as an approximation for illustration, not a substitute for the actual clinician-documented CDAI.