Clinical utility of diagnostic tests for rheumatoid factor.
OBJECTIVE
To investigate and compare the accuracy and usefulness of diagnostic tests for rheumatoid factor (RF).


METHODS
In a cross-sectional study sera derived from patients admitted to the Section of Rheumatology were tested for presence of RF using either nephelometry or the Waaler test. Diagnostic sensitivity and predictive values of the tests were calculated and compared. The accuracy of the tests was compared using receiver-operating characteristics (ROC) methodology.


RESULTS
Good agreement was found between the tests (kappa approximately 0.7). At cut-off 19 IU/mL nephelometry showed the highest sensitivity (82.4%) and specificity (95.9%) for rheumatoid arthritis (RA). In comparison, the Waaler test had a sensitivity of 60.3% and specificity of 95.9% at cut-off titer 128. The tests showed nearly equal performance characteristics when predicting SS.


CONCLUSIONS
Although both tests exhibit good performance characteristics, nephelometry has a higher accuracy when predicting RA and SS. The common practice of using both tests for detection of RF is not recommended.
Ulvestad
E
E
Department of Microbiology and Immunology, The Gade Institute, Haukeland University Hospital, Bergen, Norway. elling.ulvestad@haukeland.no
Kanestrøm
A
A
Madland
T M
TM
Thomassen
E
E
Haga
H J
HJ
D003430:Cross-Sectional Studies; D006801:Humans; D009391:Nephelometry and Turbidimetry; D011237:Predictive Value of Tests; D012372:ROC Curve; D015203:Reproducibility of Results; D012216:Rheumatic Diseases / Q000097:blood / Q000175:diagnosis*; D012217:Rheumatoid Factor / Q000097:blood
D012217:Rheumatoid Factor