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Reliability and sensitivity of diagnostic tests for primary Sjögren's syndrome
H J Haga1, B Hulten, A I Bolstad
1Medical Department B, Center for Molecular Medicine, The Gade Institute; Haukeland University Hospital, Bergen, Norway.
Objective:
To investigate whether diagnostic tests for primary Sjögren's syndrome (pSS) are reproducible when repeated after one year (reliability). To evaluate whether the sensitivity of the diagnostic tests increases with repeated testing.
Methods:
A structured interview investigating the subjective sensation of dry eyes and dry mouth, and the diagnostic tests Schirmer I, unstimulated whole saliva collection (UWSC), serological tests for antinuclear antibodies (ANA), for anti-Ro/SSA and anti-La/SSB antibodies as well as Waaler's test for rheumatoid factor, were performed twice with a one year interval in 66 patients with pSS. Reliability was given as the percentage of positive tests remaining positive at the second examination, while sensitivity was given as the percentage of patients with positive tests.
Results:
Highest reliability was obtained for the sensation of dry mouth (98.2%) and sensation of dry eyes (96.4%), and anti-SSA/SSB antibodies (93.3%). Lowest reliability was obtained for rheumatoid factor at cutoff titer 1:32 (70.6%) and positive Schirmer I in one eye (77.4%). The reliability for ANA was 80% at cutoff titer 1:32, and increased to 93.3% at cutoff titer 1:128. UWSC had a reliability of 84.2%. The pooled sensitivity for all the tests increased significantly (p < 0.05) compared to the examination, which had the lowest sensitivity.
Conclusion:
The diagnostic tests for pSS are generally highly reliable when performed twice with a one year interval. The gain in sensitivity by repeating the tests is limited, being most marked for Schirmer I.