A rapid spot immunoprecipitate assay method applied to quantitating C-reactive protein in pediatric sera

A simple, rapid spot immunoprecipitate assay (SIA) technique is compared with the rocket electroimmunoassay and a latex agglutination method for determination of C-reactive protein (CRP) in pediatric sera. The SIA reaction conditions are special, since the antigen is made passively available in a gel for reaction with an abundance of antibody. In the present study the antigen-antibody interaction occurs in the presence of alternating electric current. The reaction is visualized by protein staining and quantitated by comparison with simultaneously run standards. Highly significant (P less than 0.001) Spearman's coefficients of correlation between SIA and rocket results were found along with evidence of discrepancies between the methods which could be related to the heterogeneity in electric charge of the CRP molecules. In this respect some sera with negative (greater than or equal to 10 mg CRP/l) rocket results had two- to ten-fold higher SIA ratings. In contrast to the rocket method, SIA could differentiate sera that were negative and low positive in agglutination. Some discrepancies between an agglutination technique and SIA estimates were noted in low-positive sera differing in electromobility from the cathodic traveling CRP standard. Reproducibility of photometrically registered SIA was +/-16.2%; visually evaluated it was +/-9.7%. As little as 0.5 ng CRP was demonstrable in a human serum pool dilution at 0.17 mg/ml.