title: Regional differences in Finland in the prevalence of rheumatoid factor in the presence and absence of arthritis.
abstract: OBJECTIVE
  To look for possible regional differences in the prevalence of rheumatoid factor (RF) in the presence and absence of arthritis.
  
  
  METHODS
  The study covered a representative sample of the Finnish population aged 30 years or over, primarily comprising 8000 people, of whom 7217 participated in the field survey carried out in 1978-80. RF from serum samples from 7116 subjects was determined by the Waaler-Rose (sensitised sheep cell agglutination) test. Titres >or=32 were regarded as positive and titres >or=128 as strongly positive. Arthritis was diagnosed by a thorough clinical examination.
  
  
  RESULTS
  In the absence of arthritis the prevalence of positive and strongly positive RF reactions was 2.1% and 1.0%, respectively. The lowest prevalence of strongly "false positive" RF occurred in south western Finland. After adjustment for age, sex, smoking, and coffee consumption the odds ratio of having a strongly "false positive" RF reaction in eastern Finland was 3.16 (95% confidence interval 1.29 to 7.72) and in northern Finland 2.94 (1.13 to 7.64) compared with south western Finland. The corresponding odds ratio of strongly RF positive arthritis in eastern Finland was 5.08 (1.41 to 18.27).
  
  
  CONCLUSIONS
  Regional differences are found in the prevalence of a strongly positive RF reaction in the Finnish population. The findings are in accordance with recent results from another study concerning regional differences in the incidence of rheumatoid arthritis in Finland.
authors.affiliation: Department of Medicine, Kuopio University Hospital, Kuopio, Finland.
authors.forename: T
authors.initials: T
authors.lastname: Korpilähde
authors.forename: M
authors.initials: M
authors.lastname: Heliövaara
authors.forename: O
authors.initials: O
authors.lastname: Kaipiainen-Seppänen
authors.forename: P
authors.initials: P
authors.lastname: Knekt
authors.forename: K
authors.initials: K
authors.lastname: Aho
mesh_terms: D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000453:epidemiology; D015415:Biomarkers / Q000097:blood; D005189:False Positive Reactions; D005260:Female; D005387:Finland / Q000453:epidemiology; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D015995:Prevalence; D012217:Rheumatoid Factor / Q000097:blood*
chemical_list: D015415:Biomarkers; D012217:Rheumatoid Factor