About

The Disease Activity Score 28 (DAS28) is the global standard for assessing the activity of Rheumatoid Arthritis (RA). Unlike subjective pain scales, DAS28 combines objective laboratory markers (ESR or CRP) with specific physical examination findings. By quantifying disease activity, clinicians can make evidence-based decisions regarding the escalation or tapering of biological and DMARD therapies.

Accurate calculation is critical because treatment reimbursement and eligibility often hinge on specific DAS28 thresholds. A score difference of just 0.1 can categorize a patient differently between 'Moderate' and 'High' activity, potentially altering their access to necessary medication. This tool provides a visual interface to reduce data entry errors and supports both erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) formulas.

Formulas

The DAS28-ESR calculation relies on four variables: Tender Joint Count (TJC), Swollen Joint Count (SJC), ESR (mm/h), and the Patient Global Health (GH) assessment (0-100 visual scale).

DAS28 = 0.56 × √TJC28 + 0.28 × √SJC28 + 0.70 × ln(ESR) + 0.014 × GH

For CRP (mg/L), the constant implies a slightly different weighting:

DAS28_CRP = 0.56 × √TJC28 + 0.28 × √SJC28 + 0.36 × ln(CRP + 1) + 0.014 × GH + 0.96

Reference Data

DAS28 Score	Disease Activity Level	Clinical Interpretation
< 2.6	Remission	Goal of therapy. No significant joint inflammation.
2.6 – 3.2	Low Disease Activity	Minimal symptoms; monitor for stability.
3.2 – 5.1	Moderate Disease Activity	Evaluation for treatment adjustment required.
> 5.1	High Disease Activity	Aggressive therapy typically indicated.
Δ > 1.2	Good Response	Significant improvement from baseline.
Δ 0.6 – 1.2	Moderate Response	Some clinical benefit observed.
Δ < 0.6	No Response	Treatment likely ineffective.
Formula Used	DAS28-ESR	Standard validated metric.
Alternative	DAS28-CRP	Used when ESR is unavailable or unreliable.

Frequently Asked Questions

The DAS28 includes shoulders, elbows, wrists, metacarpophalangeal joints, proximal interphalangeal joints, and knees. Feet and ankles are excluded because they are often confounded by non-inflammatory conditions like osteoarthritis or structural damage, and studies showed the 28-joint count correlates sufficiently well with the full 66/68 joint count for monitoring RA activity.

DAS28-ESR is the original validated formula. DAS28-CRP was developed later. While they correlate well, DAS28-CRP tends to yield slightly lower scores. It is crucial to be consistent; do not switch between ESR and CRP methods when tracking a single patient's progress over time.

The Global Health assessment is a patient-reported outcome measured on a Visual Analog Scale (VAS) from 0 to 100 mm, where 0 represents 'best possible health' and 100 represents 'worst possible health'. It captures the patient's subjective perception of their disease burden.

In active disease phases, guidelines often recommend monitoring every 1-3 months. Once the treatment target (remission or low activity) is achieved, monitoring every 3-6 months is standard practice to ensure sustained control.