A simple routine method for detecting hidden rheumatoid factors.

A new and simple routine method is described for detecting hidden rheumatoid factors in human serum. EDTA glycine and NaCl were used to liberate hidden rheumatoid factors and to inactivate complement before rheumatoid-factor activity was determined in a glycine--NaCl solution. Forty-nine out of 97 sera from individuals with seronegative rheumatoid arthritis gave positive reactions by this method. Rheumatoid sera with low titres by standard tests gave higher titres with the new method. The new method detects both IgM and IgG rheumatoid factors and is simple and suitable for use in routine medical laboratories. Used in parallel with the classical tests, it facilitates detection of hidden rheumatoid factors.