Standardization and issues of rheumatoid factor measurement

OBJECTIVES: To disclose the current situation of rheumatoid factor (RF) measurement in Japan. METHOD: A small-scale survey was performed among members of the committee for the improvement of RF measurement in 2003 using manufacturers' RF reference materials valued based on WHO RF reference and pooled sera. A nationwide questionnaire survey was also performed. Questionnaires were sent to 356 educational institutes certified by the Japan College of Rheumatology in December 2004. RESULTS: The small-scale survey showed inter-laboratory differences of measured RF values, especially using RF references, and less in pooled sera. In the questionnaire survey (187 responses, recovery, 53%), qualitative or semi-quantitative RF measurement methods were used in a small number of institutes and quantitative methods were used in large numbers of institutes, the latex immunoassay (turbidimetric or nepherometric) was predominantly employed. The measuring instruments were various. The upper limit of the reference interval was distributed widely from 5 IU/ml to 40 IU/ml, indicating obvious inter-laboratory differences in RF measurement. Many institutes used the reference intervals recommended by the manufacturers. CONCLUSION: There are remarkable inter-laboratory differences in RF measurement. Clearly, one of the major issues is the lack of reference materials. We therefore need to establish a reference material of RF, even if it is a temporary one. Scientific societies (Japan College of Rheumatology and Japanese Society of Laboratory Medicine) and manufacturers providing RF measurement reagents should work together for the improvement of RF measurement.