Comparative study of test kits for measurement of rheumatoid factors by the latex fixation test.

The performance of 14 test kits for the measurement of rheumatoid factors by the latex fixation test was investigated; all results were expressed in IU/ml. Reproducibility and properties of control sera were also studied. It was found that half of the kits did not satisfactorily detect rheumatoid factor levels lower than 25 IU/ml. Most kits performed reasonably well in practice. Positive control sera only rarely met strict requirements. The relative costs did not always have a clear correlation with the quality of the results. The variation caused by differences between kits became acceptable when the results were expressed in IU/ml.