C-reactive protein (CRP) is an acute phase marker and a predictor of the risk of developing atherosclerotic complications. However, as a predictor of this risk, high sensitivity measurements are needed, and high sensitive CRP (hsCRP) assays have been developed. In this study, we experimentally compared two hsCRP assays, based on nephelometry and turbidimetry, both implemented on automated analyzers. Linearity, imprecision, turbidity interference, and results in the assay of 96 samples have been compared. Method comparison of the same two analytical systems in the assay of CRP was also performed on the basis of results in an interlaboratory external quality assessment scheme (EQAS). The two systems were found to perform substantially equally, both in hsCRP and in CRP measurement, but in the hsCRP assay the precision of nephelometry (CV% in the interval 3.0-5.8) was lower than that of turbidimetry (CV% in the interval 1.8-2.3). The classification of results by the two methods into three predefined relative risk classes gave 18% rate of discordance, in any case by one class only. The two methods proved reliable and comparable in the measurement of hsCRP, but precision should be improved.

Analytical conditions in a system for capillary zone electrophoresis (Beckman Paragon CZE 2000) were originally selected to allow serum protein separation into five discrete protein zones, corresponding to those of conventional clinical electrophoresis. To improve the system's performance, new analytical conditions have been made available. We compared the two sets of conditions ("new" = y; "old" = x) for possible variations of results caused by the change. One hundred thirteen serum samples, covering wide intervals of values, were assayed on two twin instruments working under the old and the new conditions; results were assessed statistically and graphically. Possible clinical significance of differences was checked by comparison with the biological variation-based quality specifications for bias. Statistically significant (y-x) differences were observed for the alpha1-, alpha2- and beta-globulin zones; clinically significant differences were observed for all the zones, with the exception of the gamma-globulin zone. Therefore, old/new regression equations were calculated, whose reliability was assured by the wide interval of values, by the large sample size, and by the low dispersion of single values around the mean concordance estimates. Such equations may be used to convert "old" into "new" reference values, and for the intercomparison of patient results obtained under different analytical conditions.

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Alpha-1-antitrypsin (AAT) and alpha-1-acid glycoprotein (AAG) are reported to be the main proteins contributing to the alpha-1-globulin capillary zone electrophoresis (CZE) zone, but the sum (AAT + AAG) showed lower than the alpha-1-globulin. We investigated the role of high-density lipoprotein (HDL), an additional protein migrating in the alpha-1-globulin zone, as a possible cause for such a gap. In a set of 98 sera we measured the alpha-1-globulin with a dedicated clinical capillary electrophoresis system, and AAT, AAG and apolipoprotein A-1 (ApoA) by immunonephelometry. The alpha-1-globulin were consistently higher than the sum (AAT + AAG), by (mean value +/- standard deviation) 1.70 +/- 0.88 g/L in 49 sera with low ApoA, and by 3.59 +/- 0.75 g/L in 49 sera with high ApoA. Corresponding figures in the comparison alpha-1-globulin/(AAT + AAG + ApoA) were reduced to 1.08 +/- 0.77 g/L and 1.67 +/- 0.70 g/L. It is concluded that HDL significantly contribute to the CZE alpha-1-globulin zone, but do not completely explain the differences between the electrophoretic and the immunochemical measurements. However, CZE alpha-1-globulin measurements give information about increases of the two major acute phase proteins comparable to specific protein measurements.

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