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