Diagnostic performance and clinical utility of referral rules to identify primary care patients at risk of an inflammatory rheumatic disease.

OBJECTIVE To determine the diagnostic performance and clinical utility of the Rotterdam Early Arthritis CoHort (REACH) and the Clinical Arthritis RulE (CARE) referral rules in an independent population of unselected patients from primary care. METHODS This study consisted of adults who were suspected of the need for referral towards a rheumatologist by their general practitioner. Diagnostic accuracy measures and a net benefit approach were used to compare both rules to usual care for recognizing inflammatory arthritis (IA) and inflammatory rheumatic diseases (IRD). Using the least absolute shrinkage and selection operator method and cross-validation we created an optimal prediction rule for IRD. RESULTS This study consisted of 250 patients, of whom 42 (17%) were diagnosed with IA and 55 (22%) with an IRD three months after referral. Considering IA, the AUC was 0.72 (95% CI 0.64-0.80) for the REACH and 0.82 (95% CI 0.75-0.88) for the CARE. Considering IRD, the AUC was 0.66 (95% CI 0.58-0.74) for the REACH and 0.76 (95% CI 0.69-0.83) for the CARE. The CARE was of highest clinical value when compared to usual care. The composite referral rule for IRD of ten parameters included: sex, age, joint features, acute onset of complaints, physical limitations, and duration of complaints (AUC 0.82, 95% CI 0.75-0.88). CONCLUSION Both validated rules have a net benefit in recognizing IA as well as IRD compared to usual care, however the CARE rule shows superiority over the REACH rule. Although the composite referral rule indicates a greater diagnostic performance, external validation is needed.