Counting Immunoassay for Measuring C-Reactive Protein in Serum

Abstract

We describe a simple, sensitive and rapid counting immunoassay (CIA) method which we use for measuring serum C-reactive protein (CRP) with a PAMIA-20 (Sysmex), based on latex agglutination and particle counting. The detection limit was 0.1μg/dl which is equivalent to that of RIA. The within-assay coefficient of variation (CV) ranged from 0.96% to 2.59% in the concentration range of 8.05-152.30μg/dl. The between-assay CV ranged from 2.51% to 3.41% in the concentration range of 16.2-8553.8μg/dl. The results of the counting immunoassay correlated well with those of latex photometric immunoassay using LPIA-300 (n=176, r= 0.997, y=0.969x+17.14). There was no difference in CRP values between serum and EDTA-plasma. The results obtained for the serum CRP of 234 healthy adults (119 male and 115 female) ranging from twenty to sixty years old showed the log-normal distribution in the range of 3.03-159.25μg/dl and a median value of 21.96μg/dl. Male subjects exhibited higher values (median; 29.30μg/dl) of serum CRP than those of female (median; 16.49μg/dl). Plasma CRP of 130 neonates displayed a great change several days after birth. In non-infected infants, the average plasma CRP was 119.1μg/dl (n=10, SD=108.8) on the first day. It showed a peak concentration of 432.8μg/dl (n=41, SD=536.5) on the second day, then decreased exponentially and finally reached a plateau level of 11.8μg/dl (n=7, SD=6.6) on the 7th day.