Standardization of Immunoassays for Measurement of High-Sensitivity C-reactive Protein. Phase I: Evaluation of Secondary Reference Materials

Abstract

Background: Inflammation contributes to the development and progression of atherosclerosis, and C-reactive protein (CRP) can be used as a marker to assess risk for cardiovascular diseases. As variability among existing high-sensitivity CRP (hsCRP) assays can lead to misclassification of patients and hamper implementation of population-based medical decision points, standardization of hsCRP assays is needed. Methods: We evaluated five proposed secondary reference materials, including two diluted preparations of Certified Reference Material 470 (CRM470), two preparations of a serum-based material with recombinant CRP added, and one serum-based material with isolated CRP added. Twenty-one manufacturers participated in the comparison with 28 different assays. We examined imprecision, linearity, and parallelism with these materials and with fresh serum. Results: All materials had similar imprecision; CVs for the undiluted materials were 2.1-3.7%. None of the materials was linear across all assays. Each had between one and three cases of nonlinearity, with one preparation of CRM470 having the fewest cases of nonlinearity. Although none of the materials was parallel across all assays, the differences in slope from fresh serum were similar across all assays. Conclusions: All materials performed similarly with regard to imprecision, linearity, and parallelism. As one preparation of CRM470 had slightly better characteris-

Establishment of External Quality Control Program for hs-CRP and Three-Year Follow-Up of the Performance for Precision and Accuracy

“…To overcome this problem, it is practical to incorporate common reference material and to standardize the measurement conditions as much as possible. Kimberly et al reported that unification of the reference alone does not solve variation among analytical laboratories, and varying measurement values are unavoidable due to measurement conditions, such as antibodies, measurement principles, and analytical instruments 6,8) . The gold standard of references for protein measurement is purified protein.…”

“…Preparation of purified protein is generally technically easy, but no definitive or reference method is available for hs-CRP to assign reference values for the gold standard, primary and secondary materials, or measure the serum component 6) . Thus, we considered that it is most appropriate to adopt a method in which multiple analytical laboratories measure hs-CRP using reliable measurement systems that satisfy the basic performance criteria, taking the gold standard or primary reference material as the common standard, and the mean of the measured values as the consensus value 6,8,21,22) . We established the consensus value as the target from outlier-processed measured values of the initial test analyzed by the 9 laboratories.…”

“…We established the consensus value as the target from outlier-processed measured values of the initial test analyzed by the 9 laboratories. They all calibrated the instrument using N CRP serum standardized with CRM 470 of the international plasma protein reference material 8) , because there are no globally accepted criteria for accuracy assessment 6) . These target values are the consensus values applied to our study as well as other studies commonly using sera for external QC.…”

“…Epidemiological studies are significant with regard to whether these findings are applicable to the Japanese population 3,4) . The Japan National Cardiovascular Center (NCVC) -collaborative Inflammation Cohort (JNIC) Study investigated the association of hs-CRP and arteriosclero-of hs-CRP has a normal distribution, the CV, statistic power, and 2-sided significance level were set to 2%, 80%, and 0.05, respectively, as suggested by the statistically analytical group, and the program was designed to clarify the precision, accuracy and acceptable range of accuracy for the study 6,7) . Samples that covered ranks 1 to 5 of the baseline CRP cut-off value of the 5-step categories proposed by Ridker were selected for the external QC program 2) .…”

Epidemiology and Biochemical Effects of Brucellosis in Kafer-El Sheikh and Qualyobia Cow's Farms

“…Creatinine kinase (CK) was determined according to the method described by [28]. C-reactive protein (CRP) was determined according to [29].…”