This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
Measuring rheumatoid arthritis activity
Rheumatoid arthritis is an inflammatory disease of the joints whose activity rises and falls over time. Treatment follows a treat-to-target strategy: the rheumatologist measures disease activity at each visit and adjusts treatment until the patient reaches remission or low activity. The Disease Activity Score on 28 joints (DAS28) is the most widely used composite measure for this.
The four components
- TJC28: the number of tender joints among 28 (shoulders, elbows, wrists, the ten knuckles, the ten middle finger joints counting the thumb’s, and the knees)
- SJC28: the number of swollen joints among the same 28
- ESR in mm/h or CRP in mg/L, the laboratory marker of inflammation
- GH: the patient’s global assessment of health or disease activity on a 0 to 100 mm scale
The formulas
- DAS28-ESR = 0.56 × √TJC + 0.28 × √SJC + 0.70 × ln(ESR) + 0.014 × GH
- DAS28-CRP = 0.56 × √TJC + 0.28 × √SJC + 0.36 × ln(CRP + 1) + 0.014 × GH + 0.96
The tender joint count carries twice the weight of the swollen joint count, and the square roots mean the first few joints count most.
Example
Six tender joints, four swollen joints, an ESR of 30 mm/h and a global assessment of 50:
- 0.56 × 2.449 + 0.28 × 2 + 0.70 × 3.401 + 0.014 × 50 = 5.01
- That is moderate activity, just below the high activity threshold.
Interpreting the score
| DAS28 | Disease activity |
|---|---|
| < 2.6 | Remission |
| 2.6 – 3.2 | Low |
| 3.2 – 5.1 | Moderate |
| > 5.1 | High |
The EULAR response criteria compare two scores: a fall of more than 1.2 points to a value of 3.2 or less is a good response, while a fall of 0.6 points or less is no response.
Limits
The 28-joint count leaves out the feet and ankles, so active disease there can be missed. DAS28 remission still allows a few swollen joints, which is why stricter definitions such as the Boolean ACR/EULAR remission are also used. ESR rises with age, anemia and pregnancy, so the CRP version is often preferred.