What is a DAS-28 (Disease Activity Score-28) score?

What is a DAS-28 Score?

The DAS-28 (Disease Activity Score in 28 joints) is a composite measure used to quantify rheumatoid arthritis disease activity by combining four components: a 28-joint tender count, a 28-joint swollen count, an acute-phase reactant (ESR or CRP), and patient global assessment of disease activity, calculated using a complex weighted formula. 1

Components and Calculation

The DAS28 includes the following elements:

• 28 tender joint count (weighted more heavily than swollen joints in the calculation) 1
• 28 swollen joint count 1
• Acute-phase reactant: typically ESR (DAS28-ESR), though CRP can be used (DAS28-CRP) 1
• Patient global assessment of disease activity 1

Notably, DAS28 does NOT include a provider global assessment, unlike other composite measures such as SDAI. 1

The calculation requires differential weighting of individual components and is more complex than simple arithmetic addition, typically requiring a calculator. 1

Disease Activity Categories

DAS28 scores are interpreted as follows:

• Remission: ≤2.4 (though this is less conservative than other measures like SDAI or CDAI) 1
• Low disease activity: >2.4 to ≤3.2 1
• Moderate disease activity: >3.2 to ≤5.1 2
• High disease activity: >5.1 2

Treating to a DAS28 target of ≤2.4 has been shown to improve RA outcomes. 1

Important Clinical Considerations and Pitfalls

ESR vs. CRP Versions

• DAS28-CRP and DAS28-ESR are NOT interchangeable and should not use the same cut-off values 3
• DAS28-CRP scores are generally lower than DAS28-ESR scores, which can incorrectly estimate remission 1
• ESR contributes approximately 15% of the information in DAS28-ESR 1

Potential for Misclassification

Critical pitfall: The inclusion of acute-phase reactants introduces complexity that can lead to misclassification:

• In high ESR states with few active joints, remission may be underestimated 1
• In low ESR states, remission criteria may be met despite patients having a significant number of swollen joints 1
• Newer biologic agents targeting specific inflammatory cytokines may disproportionately affect ESR and CRP, potentially deflating the composite score 1

Comparison to Other Measures

DAS28 remission criteria are less stringent than SDAI (≤3.3) or CDAI (≤2.8), meaning DAS28 may classify patients as being in remission when other measures would not. 1, 4

Unlike SDAI and CDAI, which use simple arithmetic addition:

• DAS28 requires complex differential weighting 1
• SDAI is the most sensitive and specific for predicting clinical decisions to change DMARDs 1

Practical Application

Advantages

• Well-validated and extensively used in clinical trials and practice 2, 5
• Incorporated into electronic patient records and web-based monitoring systems 5
• Useful for tight control strategies and treatment-to-target approaches 2

Disadvantages

• Requires laboratory results (ESR or CRP), which delays point-of-care calculation 1
• Complex calculation requiring a calculator or computer 1
• Examiner-dependent joint counts may be unreliable if the assessor changes 1
• Logistical barriers have delayed widespread adoption in smaller practice settings 1

Standardization of assessment methods is crucial when implementing DAS28 in clinical practice to minimize variability in the four components. 6