Utilization and predictive value of laboratory tests in patients referred to rheumatologists by primary care...

Antinuclear antibodies (ANA), rheumatoid factors (RF), and erythrocyte sedimentation rate (ESR) are among the most frequently requested tests in the diagnosis and investigation of connective tissue diseases (CTD). We evaluate the utilization patterns and predictive value of these tests in patients referred to rheumatologists by primary care physicians.

We reviewed the records of all new patients referred by primary care physicians in 1994 to 2 rheumatologists practicing at the University of Alberta. Data extracted from the records included diagnostic tests requested by referring primary care physicians, signs and symptoms at the initial rheumatology consult, and followup diagnoses.

Seven hundred eleven new patients had been referred by over 300 primary care physicians: RF had been requested in 25%, ANA in 21%, and ESR in 29%. One hundred nine (15%) of the 711 patients had a CTD, 45 (6%) had rheumatoid arthritis (RA), and 8 (1%) systemic lupus erythematosus (SLE). The predictive values of positive tests for the diagnosis of CTD were low: 49% for RF, 29% for ANA, and 35% for ESR. For RA, the positive predictive values were 44% for RF, 8% for ANA, 17% for ESR; for SLE, 2, 12, and 3%, respectively. Diffuse musculoskeletal pain and fatigue were significantly associated with test utilization, although most patients with these symptoms had fibromyalgia or localized soft tissue rheumatism.

Primary care physicians frequently requested autoantibodies in patients referred to rheumatologists. Most tests were negative, and were often requested in patients without CTD, resulting in low positive predictive values and questionable clinical utility. These findings suggest inappropriate overuse and lack of understanding of the use of autoantibody tests in diagnosing rheumatic diseases. A decrease in inappropriate use could be achieved by emphasizing that fatigue and diffuse musculoskeletal pain are not indicative of CTD in the absence of other features such as joint swelling, typical rash, or organ involvement.