Measurement of matrix metalloproteinase-3(MMP-3), a marker for rheumatoid arthritis, by means of latex agglutination turbidimetric immunoassay (LTIA), has come to replace ELISA kit, but pre-improvement LTIA kit S(Sekisui Medical) frequently shows false values resulting from non-specific reactions. We analyzed factors influencing the frequency of non-specific reactions for MMP-3 detection using various methods.
Serum MMP-3 levels were measured in 1,214 routine samples or 57 panels with various immunoserological abnormalities by means of pre-improvement and improved kit S, LTIA kit E (Eiken Chemical) and ELISA kit. Non-specific reaction samples were selected either from the routine samples based on the results of correlativity tests between the kits and of dilution linearity tests, or from 57 panels with immunoserological abnormalities based on the results of recovery tests. To explore the factors causing non- specific reactions, titers of rheumatoid factor (RF), immunoglobulins and four heterophil antibodies were measured in these samples. In addition, changes in findings as a result of reduction treatment or IgM absorption were examined in selected samples to clarify the effect of heterophil antibodies.
Samples which showed suspected false values probably due to non-specific reaction numbered 75, 15, 5 and 17 as measured with pre-improvement kit S, improved kit S, kit E and ELISA kit, respectively. Kit S also showed high rate of deviation in recovery tests on panels with immunoserological abnormalities. Rate of RF titer in samples with non-specific reactions was higher than that of other factors. Non-specific reaction could be inhibited in two samples as a result of reduction treatment or absorption of IgM subtype.
Pre-improvement kit S showed a higher rate of non-specific reactions than other kits. The most common cause of non-specific reactions is thought to be high RF titer, but high levels of IgM, including heterophil antibodies, may also affect the values of MMP-3.