HIGH PREVALENCE OF RHEUMATOID-FACTOR IN COMMUNITY-BASED SERIES OF PATIENTS WITH RHEUMATOID-ARTHRITIS MEETING THE NEW (1987) ARA CRITERIA - RF-NEGATIVE NONEROSIVE RHEUMATOID-ARTHRITIS IS VERY RARE

The aim of the study was to assess the prevalence of rheumatoid factor (RF) in a community-based rheumatoid arthritis (RA) series. The subje cts of the series represented prevalent RA cases in the Kuusamo commun ity in Northern Finland with 13,000 adult inhabitants. The patients we re selected from the official Finnish data registers and from among th e subjects who had consulted the local general practitioners due to rh eumatic complaints in the recent years, using the American Rheumatism Association (ARA) 1987 classification criteria for inclusion. For this study, ninety-five out of the 103 RA patients so found were RF-tested by immunoturbidimetry. At the time of the study. 71 (75%) of the 95 c ases were RF positive, 83 (87%) being 'ever' positive (in one case the early RF status was unclear). Our result contrasts with the much lowe r prevalence figures (25-60%) obtained from the earlier cross-sectiona l population-based RA studies. which have used the ARA 1958 definite R A as the inclusion criterion of the subjects. All the eleven patients with RF-negative RA had erosive joint disease. The RF-negative RA pati ents had a significantly lower frequency of HLA-DR4 (18%) than the RF- positive ones (58%), p < 0.05. We found a high frequency of RF among p revalent community-based RA cases meeting the ARA criteria. According to our results, RF-negative non-erosive RA is very rare among cases se lected with the above methods.