Clinical efficacy of an automated high-sensitivity C-reactive protein assay

BACKGROUND: Prospective studies have shown that C-reactive protein (CRP) can be used to predict risk of future cardiovascular events. High-sensitivity methods for CRP (hs-CRP) measurement are needed for this purpose. METHODS: We compared the clinical efficacy of an automated and commercially available latex-enhanced assay (Latex) for hs-CRP (Dade Behring) to a validated in-house ELISA, previously shown to predict future peripheral arterial disease (PAD) in asymptomatic populations. Using a prospective, nested, case-control design, we measured baseline hs-CRP concentrations in 144 apparently healthy men who subsequently developed symptomatic PAD and 144 age- and smoking habit-matched controls who remained free of vascular disease over the follow-up period of 60 months. RESULTS: The two hs-CRP assays correlated highly (r = 0.95; P <0.001), and all but two participants were classified into concordant quartiles or varied by only one quartile. The median hs-CRP of the case group was significantly higher than that of controls when measured by either the ELISA (1.34 vs 0.99 mg/L; P = 0.034) or the Latex method (1.80 vs 1.20 mg/L; P = 0.042). Furthermore, for both ELISA and the Latex method, the calculated relative risks of developing PAD increased significantly with each increasing quartile of hs-CRP. The calculated interquartile increase in relative risk of PAD was 31% (95% confidence interval, 5.2-62.2%; P = 0.01) for ELISA and 34% (95% confidence interval, 8.2-66.1%; P = 0.007) for the Latex method. CONCLUSIONS: Our findings indicate that the Latex method is equally as efficacious as the validated ELISA in classifying patients into cutoff points established by prospective studies for risk stratification for coronary and cerebrovascular disease.     

Evaluation of a high-sensitivity turbidimetric immunoassay for serum C-reactive protein: application to the study of longitudinal changes throughout normal pregnancy.

C-Reactive protein has been associated with several complications of pregnancy. The aims of the present study were: (1) to evaluate a turbidimetric immunoassay for the measurement of C-reactive protein; and (2) to investigate the chronological changes of the levels of this protein from preconception throughout normal pregnancy and its relationship with variables associated with preconception and pregnancy outcome. Inter-assay imprecision was <5% for C-reactive protein >1 mg/L and 18% at a mean value of 0.33 mg/L. The limit of detection was 0.10 mg/L. The method was linear between 0.10 and 30 mg/L. There were no observed interferences from jaundice, hemolysis, lipemia or paraproteinemia at the levels studied. There was good agreement with the nephelometric method. A total of 39 women were studied at preconception, at 8, 20 and 32 weeks of pregnancy, and in labor. Preconception C-reactive protein concentration was 1.17+/-0.18 mg/L and increased (p<0.001) throughout pregnancy up to 5.69+/-0.82 mg/L. Body mass index at preconception and weight gain during pregnancy were the main factors associated with this increase in C-reactive protein.     

Development of a point-of-care assay system for high-sensitivity C-reactive protein in whole blood

BACKGROUND: C-reactive protein (CRP) is emerging as a potential risk predictor for future cardiovascular diseases (CVD). High sensitivity assays have been developed and applied for clinical purposes. METHODS: The fluorescence immunochromatographic assay was employed to detect and quantify CRP in whole blood. It consisted of a fluorescence (FL) antibody detector buffer, a test strip housed in a disposable cartridge, and a laser fluorescence scanner. Whole blood sample was mixed with detector, loaded onto a cartridge, incubated for 10 min, and the concentration of CRP was measured in a laser fluorescence scanner. The linearity, limit of detection (LOD), and performance of new assay system was tested and evaluated. The comparability of assay was examined with an automated reference method. RESULTS: With the new assay system, a reliable correlation of coefficient (r) was obtained between the ratio value (A(T)/A(C)) and a concentration of CRP in samples. The linearity fell in the range of 0-10 mg/l of CRP, and the analytical detection limit was 0.133 mg/l of CRP. The mean recovery of the control was 105.2% in a working range. The precision of the intra- and inter-assay in a range of 0.5-6 mg/l was CVs <6% and <8%, respectively. The new fluorescence immunochromatographic assay system correlated well with a traditional immunoturbidimetric assay for quantification of CRP concentration (r=0.955, N=90). CONCLUSION: The fluorescence immunochromatographic assay is fast, reliable, and a reproducible platform for point-of-care testing (POCT) of high-sensitive (hs)-CRP in whole blood.     

C-reactive protein and high-sensitivity C-reactive protein: an update for clinicians

The measurement of C-reactive protein (CRP) using both standard and high-sensitivity CRP (hs-CRP) assays is becoming common in clinical practice. This article addresses the causes of CRP elevation and the use of different CRP assays in internal medicine, including cardiology, gastroenterology, rheumatology, infectious diseases, and oncology. We focus on the recent medical literature on the use of hs-CRP in cardiovascular disease risk stratification and management, including updated screening guidelines on the use of hs-CRP, such as those issued in 2009 by the Canadian Cardiovascular Society. We also discuss the Reynolds Risk Score, which incorporates hs-CRP and family history with more standard cardiovascular risk factors (eg, tobacco use, hypertension, and dyslipidemia) and frequently leads to improved recategorization of cardiovascular disease risk levels. As the recently completed Justification for the Use of Statins in Prevention: An Intervention Trial Evaluating Rosuvastatin (JUPITER) trial indicated that statin therapy decreases the vascular events among persons with elevated hs-CRP by half, even when cholesterol levels are low, the inclusion of information on hs-CRP values with other cardiovascular risk factors may assist physicians in medical decision making for patients.     

Performance characteristics of an automated high-sensitivity C-reactive protein assay on the Dimension RXL analyzer

BACKGROUND: C-reactive protein (CRP) is a nonspecific marker of inflammation that can be used as a marker for atherosclerotic risk. This application requires increased precision at low CRP concentrations compared to traditional assays. METHODS: The Dimension RXL is an automated chemistry analyzer for central laboratory use. The limit of detection, limit of quantification, linearity and imprecision of a high-sensitivity CRP assay developed for it were assessed. Method comparison studies were performed using samples both inside and outside the reference interval. The presence of a prozone effect was also evaluated. RESULTS: The limit of detection was 0.7 mg/l. The method was linear from 2 to 60 mg/l and from 1 to 60 mg/l using systematic error limits of 10% and 20%, respectively. The total imprecision was <10% for CRP concentrations above 1.5 mg/l. No prozone effect was seen at a CRP concentration of 450 mg/l, the highest concentration tested. Using samples from 212 apparently healthy adults, the Dimension RXL method demonstrated good concordance with the BN II high-sensitivity CRP method for samples in the highest quartile. It also compared well using samples with elevated CRP concentrations. CONCLUSIONS: The Dimension RXL high-sensitivity CRP method may be adequate for atherosclerotic risk prediction in clinical practice if accurate and precise measurement is only required for the highest quartile. However, the total error of this method for CRP concentrations <3 mg/l appears too large for accurate assignment to lower risk groups.     

Analytical performance and clinical efficacy for cardiovascular risk estimation of an Olympus immunoturbidimetric high-sensitivity C-reactive protein assay.

Increased C-reactive protein (CRP) concentration within the reference interval (<10.0 mg/L) is a strong predictor of cardiovascular disease (CVD) in apparently healthy adults. Cutoff points for use of CRP in estimating CVD risk are <1, 1-3 and >3 mg/L for low, average and high relative risk, respectively. For measuring CRP concentrations to assess cardiovascular risk, high-sensitivity CRP (hsCRP) assays have been developed. The aim of this study was to evaluate the analytical performance and clinical efficacy for cardiovascular risk estimation of the Olympus immunoturbidimetric latex CRP assay (sensitive application). The comparative method used was the CardioPhase* hsCRP assay, approved by the Food and Drug Administration for use in CVD risk assessment. The imprecision of the Olympus hsCRP assay in the concentration range 0.2-10.0 mg/L was 0.38-8.16% within runs and 3.75-9.63% between runs. For method comparison studies, 194 fresh serum samples were selected to cover the interval 0.15-10.0 mg/L CRP. Comparison of the Dade Behring and Olympus methods was performed using weighted Deming regression analysis (slope 0.99 mg/L, intercept 0.002 mg/L, S(y,x)=0.02 mg/L, r=0.992) and a Bland-Altman relative difference plot (mean difference -0.002%, SD=0.040%). The agreement between the Dade Behring and Olympus methods for relative risk class assignments was 95.4%. Statistical analysis of the agreement between the two methods for each relative risk class showed that the differences between the methods were not statistically significant (p>0.10). Although previous reports found poor performance of the Olympus CRP tests for use in cardiovascular and peripheral vascular risk estimation, our study proved good analytical performance and clinical efficacy of the Olympus hsCRP assay for this use.     

Evaluation of four automated high-sensitivity C-reactive protein methods: implications for clinical and epidemiological applications

BACKGROUND: C-reactive protein (CRP) can provide prognostic information about the risk of developing atherosclerotic complications in apparently healthy patients. This new clinical application requires quantification of CRP concentrations below those traditionally measured in the clinical laboratory. METHODS: The Dade Behring BN II, the Abbott IMx, the Diagnostic Products Corporation IMMULITE, and the Beckman Coulter IMMAGE are four automated analyzers with high-sensitivity CRP (hs-CRP) methods. We evaluated these assays for precision, linearity, and comparability with samples from 322 apparently healthy blood donors. RESULTS: The imprecision (CV) of the BN II, IMx, IMMULITE, and IMMAGE methods was < or = 7.6%, < or = 12%, < or = 9.8%, and < or = 9.7% at 3.5 mg/L, respectively. The BN II, IMx, IMMULITE, and IMMAGE methods were linear down to < or = 0.30, < or = 0.32, < or = 0.85, and 2.26 mg/L, respectively. CRP concentrations demarcating each quartile in a healthy population were method dependent. The IMx method gave results comparable to the BN II method for values in the reference interval. The IMMULITE method had a positive intercept compared with the BN II method. The IMMAGE method demonstrated more scatter and a positive intercept compared with the BN II method, which may reflect the fact that it is a less sensitive assay. CONCLUSIONS: The four hs-CRP methods exhibited differences in results for a healthy population. Additional standardization efforts are required to ensure that hs-CRP results can be related to large-scale epidemiologic studies.     

Evaluation of nine automated high-sensitivity C-reactive protein methods: implications for clinical and epidemiological applications. Part 2

BACKGROUND: C-Reactive protein (CRP) can provide prognostic information about risk of future coronary events in apparently healthy subjects. This application requires higher sensitivity assays than have traditionally been available in the clinical laboratory. METHODS: Nine high-sensitivity CRP (hs-CRP) methods from Dade Behring, Daiichi, Denka Seiken, Diagnostic Products Corporation, Iatron, Kamiya, Olympus, Roche, and Wako were evaluated for limit of detection, linearity, precision, prozone effect, and comparability with samples from 388 apparently healthy individuals. RESULTS: All methods had limits of detection that were lower than the manufacturers' claimed limit of quantification except for the Kamiya, Roche, and Wako methods. All methods were linear at 0.3-10 mg/L. The Diagnostic Products Corporation, Kamiya, Olympus, and Wako methods had imprecision (CVs) >10% at 0.15 mg/L. The Iatron, Olympus, and Wako methods demonstrated prozone effects at hs-CRP concentrations of 12, 206, and 117 mg/L, respectively. hs-CRP concentrations demarcating each quartile in a healthy population were method-dependent. Ninety-two to 95% of subjects were classified into the same quartile of hs-CRP established by the Dade Behring method by the Denka Seiken, Diagnostic Products Corporation, Iatron, and Wako methods. In contrast, 68-77% of subjects were classified into the same quartile by the Daiichi, Kamiya, Olympus, and Roche methods. No subject varied by more than one quartile by any method. CONCLUSIONS: Four of the nine examined hs-CRP methods classified apparently healthy subjects into quartiles of hs-CRP similar to the classifications assigned by the comparison method. Additional standardization efforts are required because an individual patient's results will be interpreted using population-based cutpoints.     

Development of a new microparticle-enhanced turbidimetric assay for C-reactive protein with superior features in analytical sensitivity and dynamic range

Novel assay techniques were applied to a newly developed microparticle-based assay for C-reactive protein (CRP). By using two different sized microparticles covalently coated with two monoclonal antibodies of different reactivity, high analytical sensitivity and a high upper measuring limit could be simultaneously attained, resulting in a remarkably wide dynamic range. This range was further increased by calculating the signal (reaction rate) optimally with a new software capability of COBAS® INTEGRA, a clinical chemistry analyzer. The assay showed high precision between 2 mg/l and 160 mg/l with use of only 2.5 μl specimen. The detection limit was estimated as 0.3 mg/l CRP. The assay was four to eight times more sensitive and precise than existing turbidimetric or nephelometric assays with comparable upper measuring limits. The assay also showed good linearity and correlated well with commercial assays. This new microparticle-based CRP assay provides the accuracy and precision that are required to determine CRP at low concentrations where new clinical implications such as prognosis of cardiovascular diseases are envisaged. The assay's wide dynamic range will additionally lead to a reduction in the number of repeated analyses, thus improving the efficiency of CRP determinations in clinical laboratories. J. Clin. Lab. Anal. 12:137–144, 1998. © 1998 Wiley-Liss, Inc.     

Analyzer transfer of a broad range high-sensitivity C-reactive protein immunoassay

C-reactive protein (CRP) is measured in two main clinical situations: inflammation, where levels in the range of 5-300 mg/L are expected, and, more recently, assessment of the cardiovascular risk, where concentrations between 0.1 and 10 mg/L shoud be determined. Few commercially available methods display a measuring range covering both zones and laboratories are compelled to use two different assay protocols or even two different methods. The aim of the study was to adapt the Roche C-Reactive Protein (Latex) kit, initially developed for the Roche Cobas Integra analyzers, to the Hitachi Modular P800 analyzer in order to obtain on this instrument a broad range assay for CRP measurement. The method was successfully adapted and validated against a high-sensitivity and a traditional assay. The resulting method correlates well with the other two and displays a measuring range of 0.10-171 mg/L with an imprecision lower than 5.5%. This assay could be particularly practical in the routine clinical laboratory, being suitable for every use of CRP measurements.     

血清高敏C-反应蛋白在心血管病变中的表达特性

目的　探讨心血管病变血清高敏C 反应蛋白 (hs CRP)的表达特性。方法　采用胶乳增强免疫 (超敏 )比浊法 ,定量检测健康对照组 340名、冠脉造影患者 341例、心肌梗死患者 86例血清hs CRP。结果　 (1 )健康对照组hs CRP呈明显的偏态分布 ,hs CRP中位数 :0 45mg/L ,95 %位数 :3 0 7mg/L ,经对数转换hs CRP均数为 (0 76± 1 2 9)mg/L ,存在性别和年龄差别。 (2 )冠脉造影阳性组 (2 1 4例 )hs CRP :(2 1 8± 2 71 )mg/L ,冠脉造影阴性组 (1 2 7例 )hs CRP :(1 46± 1 66)mg/L ,差异有显著意义(t=2 638,P <0 0 1 )。急性心肌梗死组hs CRP :(6 0 8± 4 55)mg/L。脉造影阳性组hs CRP随阳性支数增加而增高。hs CRP对冠心病的临床评价ROC曲线下面积为 0 81 0。结论　hs CRP对健康人心血管病变的存在和发生心血管意外预测和预防具有重要意义。     

超敏C反应蛋白在冠心病中的表达特性

目的探讨血清超敏C反应蛋白(hsCRP)在冠心病中的表达特性。方法随机选取115例经冠脉造影证实的冠心病患者,包括稳定型心绞痛(SAP)39例,不稳定型心绞痛(UAP)34例,急性心肌梗塞(AMI)42例,50例健康人作为对照组。在OlympusAU2700全自动生化分析仪上应用乳胶增强免疫透射比浊法测定血清中hsCRP的浓度,并分析治疗前后hsCRP水平的差异。结果冠心病患者中hsCRP浓度与对照组相比明显增高,差异具有统计学意义(P<0.01)。AMI组hsCRP水平明显高于UAP组,UAP组hsCRP水平明显高于SAP组,均有统计学意义(P<0.01)。冠心病各组的hsCRP水平在治疗前后比较有统计学意义(P<0.01)。结论冠心病患者血清hsCRP水平显著增高,提示冠心病患者可能存在炎症反应。检测hsCRP对冠心病的辅助诊断、疗效观察及预后判断具有重要价值。     

超敏C反应蛋白与冠状动脉狭窄程度的相关性研究

的相关性.方法 采用胶乳增强免疫透射比浊法检测经冠状动脉造影（CAG）确诊的CHD患者100例和CAG结果正常者40例的血清hs-CRP浓度,同时采用Gensini评分系统对CHD患者冠状动脉血管病变程度进行定量评分,并分析hsCRP与Gensini评分间的关系.结果 血清hs-CRP浓度在单支冠状动脉病变组、双支冠状动脉病变组及三支冠状动脉病变组依次增高,均显著高于对照组,差异有统计学意义;且CHD患者血清hs-CRP水平与Gensini积分呈显著正相关（r=0.316,P＜0.01）.结论 血清hs-CRP水平与冠状动脉病变的程度有相关性,可作为临床评价冠状动脉狭窄程度的指标之一.