Nephelometry v differential agglutination titre in the measurement of rheumatoid factors

IgM rheumatoid factors have been measured in 92 patients by both laser nephelometry and the traditional hospital procedure of a latex slide test followed by differential agglutination titre (DAT). Of the results 86% were in accordance by both methods, but seronegative patients with a high nephelometry score all showed, after reference to their clinical state and previous investigations, that the nephelometry result more accurately represented their clinical state than the DAT, which was shown to be in error in five out of the six cases. Six seropositive patients with low nephelometry scores were also studied; three were in complete remission on gold or penicillamine therapy. Nephelometry is both technically simpler and more reliable than the traditional DAT method, and our results suggest that it has some advantages over the DAT in routine use.