Effect of baseline rheumatoid factor (RF) levels on DAS28-response to standard DMARD-combination treatment in patients with rheumatoid arthritis (RA)

Objective: Rheumatoid factor (RF) positivity has been associated with an unfavourable outcome in rheumatoid arthritis (RA). Our study aimed to find a baseline RF cut-off level that would determine the response to standard disease modifying anti-rheumatic drug (DMARD) combination treatment. Patients and methods: We studied 233 seropositive (RF levels ≥20 IU/mL at presentation) RA patients over a period of up to 5 years. Disease activity was assessed at each patient-encounter using disease activity score on 28 joints (DAS28). Treatment consisted of weekly methotrexate, daily hydroxychloroquine and low dose oral methlyprednisolone as an adjunct. Sulfasalazine or leflunomide were added to the ongoing regimen if satisfactory response was not achieved by 3 months of treatment. Individual response of patients to treatment was graded using the following DAS28 cut-off values: <3 as low disease activity (satisfactory response), ≥3 as moderate and ≥5.1 as high (unsatisfactory response). Results: By analyzing all possible 2 x 2 contingency tables based on the different values of RF in the data set, using Fisher's exact test of association between RF levels and DAS28 values, a cut-off level for RF of 70 IU/mL gave the optimal discrimination between 'low' versus 'moderate or high' disease activity in the follow-up. Conclusion: A baseline RF cut-off value of 70 IU/mL appears to predict a 'satisfactory' versus 'unsatisfactory' response to standard DMARD-combination therapy in RA over time.