Smoking history and serum cotinine and thiocyanate concentrations as determinants of rheumatoid factor in non-rheumatoid subjects.

OBJECTIVES: Smoking is associated with false-positive rheumatoid factor (RF). We explored the dose-response relationship of this association, using smoking history and serum cotinine and thiocyanate concentrations as measures of tobacco exposure. METHODS: A total of 6947 men and women aged 30 yr or over and free of clinical arthritis were included in the Mini-Finland Health Survey carried out between 1978 and 1980. Detailed histories of smoking and RF (sensitized sheep cell agglutination test) were obtained in the basic examination. In 2000, serum cotinine and thiocyanate were determined from serum samples collected at baseline and stored at -20 degrees C. A cut-off point of 100 microg/l was used for serum cotinine and 10 micromol/l for thiocyanate to indicate active smoking. RESULTS: There was a close association between smoking and strongly positive RF. After adjustment for age, sex, coffee consumption and region, the odds ratios (95% confidence intervals in brackets) in current smokers and in those who had quit smoking were 3.94 (2.04-7.61) and 2.71 (1.33-5.53), respectively, compared with those who had never smoked. Among current smokers, the intensity, duration or tertiles of pack-years of smoking were not related to RF. No relationship between serum cotinine or thiocyanate and RF positivity was observed within the subgroups of current smokers and those who had quit. Among those who reported that they had never smoked but who nevertheless had serum cotinine levels at least 100 microg/l, the adjusted odds ratio of strongly positive RF was 4.48 (1.48-13.50) compared with people who had never smoked and whose serum cotinine levels were less than 100 microg/l. CONCLUSIONS: The results are not in line with the hypothesis of a dose-response relationship between smoking exposure and RF positivity.

Regional differences in Finland in the prevalence of rheumatoid factor in the presence and absence of arthritis.

OBJECTIVES: 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). CONCLUSION: 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.