[Use of rheumatoid factor IgM analysis. A questionnaire study among the users]

The aim of this study was to describe who orders the rheumatoid factor analysis (RF-IgM) and the clinical indication compared to the result of the analysis. All analyses over a one month period were registered. The doctor who had ordered the analysis was contacted in order to answer a questionnaire asking about the clinical symptoms, results of other analyses and whether this analysis were the first or more. Four hundred and sixty-seven analyses were registered (population: about 300,000), 21% with a positive ELISA result (cut-off: 6 IU/ml). Thirty-one percent of the patients had clinical symptoms associated with rheumatoid arthritis. Sixty-seven percent of the analyses were ordered by the general practitioner. If we changed the cut-off to 15 or 20 IU/ml only 14 or 12 analyses were registered as having a positive result. We conclude that the analysis is often used for case-finding, perhaps the frequency could be reduced if the analysis were used more specifically and that the doctor who receives the answer has to be aware of the influence of the cut-off used by the local laboratory.