Utilization & predictive value of laboratory tests in patients referred to rheumatologists by primary care physicians

OBJECTIVE: 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


METHODS: 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.

RESULTS: 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.

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