[The diagnostic value of anti-SSA antibody in primary Sjögren's syndrome]

According to international classification criteria (2002) on Sjögren's syndrome, labial pathology was still considered as a major criterion for diagnosis. Standard labial biopsy was hard to be carried out in China. This study is to evaluate whether the invasive labial biopsy could be replaced by noninvasive detection of serum anti-SSA antibody.

181 Chinese patients with the initial diagnosis of primary Sjögren's syndrome in Peking Union Medical College Hospital (PUMCH) were enrolled in Sjögren's International Collaborative Clinical Alliance (SICCA). All patients received standard labial biopsies (area of salivary gland tissue ≥ 4 mm²) and focal score (FS) of focal lymphatic sialadenitis were confirmed by pathologists from school of stomatology, University California of San Francisco (UCSF). Anti-SSA antibodies in sera of all patients were detected by double immunodiffusion (DID), Western blot in PUMCH and by enzyme-linked immunosorbent assay (ELISA) in central laboratory of SICCA. The correlation between labial pathological findings and serum anti-SSA antibody was studied by chi² test and the concordance was calculated by unweighted Kappa.

(1) Bivariate analysis revealed strong associations of FS > 1 with the presence of anti-SSA antibody by DID (83.9% vs 42.0%, P < 0.0001). The accordance between FS and antibody detection by DID was fine with a kappa value of 0.432. However, there were 16.1% false-positive antibody reports and 42.0% false-negative antibody reports. (2) FS > 1 was strongly associated with the presence of anti-SSA antibody by Western blot (83.0% vs 51.7%, P < 0.0001). But the accordance between FS and antibody detection by Western blot was only fair with a kappa value of 0.316. There were 17.0% false-positive antibody reports and 51.7% false-negative antibody reports. (3) FS > 1 was strongly associated with the presence of anti-SSA antibody by ELISA (81.5% vs 38.6%, P < 0.0001). The accordance between FS and antibody detection by ELISA was fine with a kappa value of 0.427. There were 18.5% false-positive antibody reports and 38.6% false-negative antibody reports.

In Sjögren's syndrome, labial biopsy with FS > 1 finding is strongly associated with anti-SSA antibody. Positive results of anti-SSA antibodies by DID or ELISA may indicate FS > 1, thus labial biopsy could relatively be avoided, negative results may need further standard labial biopsy procedure to confirm the diagnosis of Sjögren's syndrome.