In the era of nephelometry, latex agglutination is still good enough to detect rheumatoid factor.

Abstract

To compare quantitative nephelometry to the traditional semiquantitative latex agglutination (LAT) test for rheumatoid factor (RF). We evaluated 564 patients with rheumatoid arthritis (RA) and 155 controls using both techniques. The cutoff value of 40 IU/ml was established for a positive RF result. Sensitivity of LAT and nephelometry was 85.5% and 88.3%, respectively. Both techniques had a similar specificity and a positive predictive value exceeding 95%. Agreement (kappa = 0.86) and correlation (0.87) between the 2 methods were significant. In routine practice, and particularly in developing countries such as India, LAT can still be the preferred method for RF determination.