[A consideration on discrepancy of results obtained between commercial CRP measurement kits]

We investigated the frequency of the occurrence of discrepancies using various patients' sera between several commercial C reactive protein(CRP) kits with turbidimetric immunoassay, and the elucidation of the mechanism of the non-specific reaction, also investigated methods of minimizing false results in some procedures. CRP was measured in 79 patients' sera containing monoclonal immunoglobulins [Multiple Myeloma: 45 patients' sera(IgG type, 37; IgA type, 7; BJP type, 1); Waldenström's disease: 8; Benign M proteinemia: 26], 70 patients' sera with polyclonal high gamma-globulinemia (> 2.0 g/dl) and 91 patients' sera with positive rheumatoid factor. Two different patients' sera, one(chronic hepatitis C) with Waldenström's disease and the other(purpura) with polyclonal high gamma-globulinemia, showed marked discrepancies. We found these discrepancies were induced by milky turbidity produced by non-specific reaction between high molecular weight components(cryoglobulin composed from IgM-IgG in the Waldenström case and immune complex in the polyclonal high gamma-globulinemia case), and the buffer solution contained polyethylene glycol(PEG) as a catalyst. The discrepancy was minimized by the following procedures: (a) decreasing the PEG concentration, (b) increasing pH of the buffer solution, (c) using a small volume of the secondary reagent(R2), and (d) using rabbit anti-human CRP serum instead of goat serum.