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Disease Activity Assessment

Multiple indices have been developed to measure disease activity in RA. Some specific indices, such as the Disease Activity Score 28 (DAS28) and the Simplified Disease Activity Index (SDAI), require laboratory testing in addition to physical examination, whereas the Clinical Disease Activity Index (CDAI), the Rheumatoid Arthritis Disease Activity Index (RADAI), the Patient Activity Scale (PAS), and the Routine Assessment Patient Index Data (RAPID) rely on a combination of patient- and physician-reported activity measures in addition to examination of the joints.¹ A recent report found that the patient-administered RADAI correlated well with the DAS28 in assessing disease activity in patients experiencing an RA flare.² The new ACR recommendations provide cut points for low, moderate, and high disease activity across the various instruments (Table 1).¹ No recommendations favoring any specific indices were made, but, in general, quantification of disease activity is necessary to make evidenced-based decisions about treatment.¹ According to Dr. Saag, not all rheumatologists are currently using a disease activity instrument, because of the time involved and other challenges such as additional laboratory testing required.¹ The ACR Task Force specifically chose not to recommend the use of any particular disease activity instruments, since certain measures work better than others in different clinical practice settings. New performance measures developed by the National Committee on Quality Assurance (NCQA) recommend that disease activity be assessed and classified every 12 months at minimum.¹ As Dr. Saag noted, assessing and classifying disease activity provides objective evidence that can be used to guide the appropriate initiation of specific therapies, particularly biologic therapies.

Table 1. Instruments and disease activity cut points for RA.¹

In addition to measures of disease activity, the recommendations cite various factors that have been determined to be prognostic in RA. These include active disease with high counts for tender and swollen joints, the presence of joint erosion, elevated levels of rheumatoid factor, the presence of anti-cyclic citrullinated peptide (anti-CCP) antibodies, elevated erythrocyte sedimentation rate (ESR), elevated C-reactive protein (CRP) levels, worse physical functioning as indicated by scores on the Health Assessment Questionnaire, and the presence of the HLA-DRB1 genotype.¹ The presence of anti-CCP antibodies prior to and at the time of disease onset has been associated with a more aggressive form of RA; the presence of both anti-CCP antibodies and rheumatoid factor has predicted disease progression on radiographic examination when combined with swollen joint count and Larsen score.⁴ Levels of anti-CCP antibodies also correlate with therapeutic response; ie, antibody levels decrease in patients responding to treatment.⁴ Persistently elevated ESR (≥52 mm/hr) and CRP level (≥3 mg/dL) during treatment with methotrexate has been associated with greater progression on radiography.⁵ Patient health status, as indicated by scores on the Health Assessment Questionnaire in the first 3 months of the disease, has been identified as a strong predictor of patient outcomes 10 years later.⁶