OBJECTIVE: Rheumatoid factor (RF) testing is used in primary care in the diagnosis of rheumatoid arthritis (RA); however a positive RF may occur without RA. Incorrect use of RF testing may lead to increased costs and delayed diagnoses. The aim was to assess the performance of RF as a test for RA and to estimate the costs associated with its use in a primary care setting. MATERIAL AND METHODS: A retrospective cohort study using the Information System for the Development of Research in Primary Care database (contains primary care records and laboratory results of >80% of the Catalonian population, Spain). Participants were patients ≥18 years with ≥1 RF test performed between 01/01/2006 and 31/12/2011, without a pre-existing diagnosis of RA. Outcome measures were an incident diagnosis of RA within 1 year of testing, and the cost of testing per case of RA. RESULTS: 495,434/4,796,498 (10.3%) patients were tested at least once. 107,362 (21.7%) of those tested were sero-positive of which 2768 (2.6%) were diagnosed with RA within 1 year as were 1141/388,072 (0.3%) sero-negative participants. The sensitivity of RF was 70.8% (95% CI 69.4-72.2), specificity 78.7% (78.6-78.8), and positive and negative predictive values 2.6% (2.5-2.7) and 99.7% (99.6-99.7) respectively. Approximately €3,963,472 was spent, with a cost of €1432 per true positive case. CONCLUSIONS: Although 10% of patients were tested for RF, most did not have RA. Limiting testing to patients with a higher pre-test probability would significantly reduce the cost of testing.
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Artritis reumatoide, Atención primaria, Electronic health records, Especificidad, sensibilidad, Factor reumatoide, Historia clínica informatizada, Primary care, Rheumatoid arthritis, Rheumatoid factor, Sensitivity specificity, Adult, Aged, Arthritis, Rheumatoid, Cohort Studies, Costs and Cost Analysis, Female, Hematologic Tests, Humans, Male, Middle Aged, Primary Health Care, Retrospective Studies, Rheumatoid Factor, Sensitivity and Specificity, Spain