Diagnostic characteristics of a gelatin based Waaler-Rose assay (Serodia-RA) for the detection of rheumatoid factor.
OBJECTIVE
To evaluate the diagnostic usefulness of a gelatin based Waaler Rose assay (Serodia-RA) for the detection of rheumatoid factor (RF) in rheumatoid arthritis (RA).


METHODS
RF was measured by Serodia-RA and rate nephelometry in 90 patients with RA according to the revised ACR criteria and 102 patients with rheumatological diseases other than RA. Sensitivity, specificity, accuracy, likelihood ratios, and area under the curve using receiver operating characteristics (ROC) analysis were determined for both tests. Agreement between assays was assessed on 1657 consecutive samples.


RESULTS
At equal specificity, Serodia-RA tended to be more sensitive than rate nephelometry (0.66 v 0.58; p = 0.04). ROC plots showed an area under the curve of 0.843 for Serodia-RA and 0.784 for nephelometry, providing further evidence that Serodia-RA was slightly better at differentiating between RA and non-RA arthropathy. Good agreement was found between both assays.


CONCLUSIONS
Serodia-RA is slightly more accurate than rate nephelometry for the detection of RF in RA, and a combination of both assays only marginally improves the diagnostic usefulness of RF detection. Use of two tests for detection of RF is not recommended. One test for detection of RF together with a more specific test, such as antibodies to cyclic citrullinated peptide, is suggested.
Department of Laboratory Medicine, University Hospitals Leuven, Belgium.
T
T
Spiritus
P
P
Verschueren
R
R
Westhovens
X
X
Bossuyt
D000328:Adult; D000372:Agglutination Tests / Q000379:methods; D001172:Arthritis, Rheumatoid / Q000175:diagnosis*; D015415:Biomarkers / Q000097:blood; D003937:Diagnosis, Differential; D005780:Gelatin; D006801:Humans; D008875:Middle Aged; D009391:Nephelometry and Turbidimetry; D012372:ROC Curve; D012216:Rheumatic Diseases / Q000175:diagnosis; D012217:Rheumatoid Factor / Q000097:blood*; D012680:Sensitivity and Specificity
D015415:Biomarkers; D005780:Gelatin; D012217:Rheumatoid Factor