Comparison of three immunoassays for C-reactive protein determination.

Three widely used immunoassays for C-reactive protein (CRP) determination (RID. RIEP and LN--Behring) were compared. According to the CRP calcium dependent structural changes or ligand binding properties two buffer systems, Ca2+ rich and Ca2+ depleted, were used in all methods. In RID and RIEP mean values of studied samples were higher when Ca2+ depleted buffer was used (r = 0.94 and r = 0.88, respectively). However, in LN mean values of studied samples were higher when Ca2+ rich buffer was employed (r = 0.923). Comparison of RID and RIEP showed better correlation when Ca2+ depleted buffer was used with r = 0.913 and regression equation y = 0.92 chi + 2.76. Comparison of RID with LN gave similar results as in the case of RIEP and LN. In both cases mean values of studied samples were much higher in LN. Best correlation between RID and LN was obtained when RID was run in Ca2+ depleted buffer and LN performed in Ca2+ rich buffer (r = 0.845, y = 1.25 chi + 18.4). When RIEP and LN were compared highest correlation was obtained when Ca2+ rich buffer in both methods had been used (r = 0.84, y = 1.45 chi + 33.7). However, comparison of both methods run in Ca2+ depleted buffer yielded better regression equation: y = 1.05 chi + 26.1 with r = 0.795.