Comparison of the different classification criteria sets for primary Sjögren's syndrome.

Objective: To assess the comparability of different classification criteria sets for primary Sjögren's syndrome (pSS).

Methods: In a prospective study we examined all patients with suspected pSS who were admitted to our Department of Rheumatology or referred to our outpatient clinic between 1 January 2001 and 31 December 2002. The Copenhagen, Californian, 1996 European, and American-European consensus group (US-EU) criteria sets were used to assess each patient.

Results: Ninety out of 222 patients (41%) were diagnosed with pSS by fulfilling at least one classification criteria set. The highest number of patients who were diagnosed with pSS fulfilled the European criteria set (36%), followed by the Copenhagen (28%), the US-EU (26%), and the Californian (9%) criteria sets. On average, the group of patients fulfilling the Californian criteria set were 5.6 years older than the patients in the other three groups (p < 0.05). In addition, the disease duration before diagnosis was 2.6 years longer than in the other three groups. The groups of patients fulfilling either the Californian or the US-EU criteria sets had a higher prevalence of leucopaenia (p < 0.05). Those fulfilling the US-EU criteria set also had a higher prevalence of arthritis (p < 0.05). No significant differences were found in the prevalence of the other clinical and laboratory parameters studied.

Conclusions: Different patients are diagnosed with pSS if different classification criteria sets are used. Therefore, studies based on different classification criteria sets for diagnosing pSS are not directly comparable.