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Quartile Agreement Quartile Agreement

Fig. 5. Agreement among various hsCRP methods using sample from apparently healthy individuals The Dade-Behring hsCRP method was used as the comparison method. (With permission from ref.58.)

significant discrepancy in reported results and emphasized the need for additional standardization (59,60). For example, in one evaluation study, four ofthe hsCRP methods were in excellent agreement with the comparison method in classifying subjects into quartiles of risk (59) (Fig. 5). In fact, 92-95% of subjects were classified by these methods into the exact quartile and the remaining 5-8% fell almost equally into the adjacent two quartiles. Using the other four methods, however, only 65-75% of subjects were classified into the exact quartile, and the remaining 25-35% fell into the adjacent upper quartile, indicating a problem with standardization. Agreement among the various hsCRP methodologies

LDL Cholesterol (mg/dL) Fig. 6. Algorithm for risk assessment of CHD. CRP cut points are those recommended by the AHA/ CDC expert panel and LDL cholesterol cut points are those recommended by the National Cholesterol Education Program. Risk estimates are not adjusted for other CHD risk factors. (With permission from ref. 17.)

LDL Cholesterol (mg/dL) Fig. 6. Algorithm for risk assessment of CHD. CRP cut points are those recommended by the AHA/ CDC expert panel and LDL cholesterol cut points are those recommended by the National Cholesterol Education Program. Risk estimates are not adjusted for other CHD risk factors. (With permission from ref. 17.)

is essential, considering that the individual patient's results will be interpreted within the context of nationally established cut points. To address this issue, the CDC initiated a standardization program to which manufacturers of all hsCRP reagents worldwide have been invited to participate (8). Phase I of this project aimed to identify a suitable reference material. The use of a common calibrator among the various assays usually leads to a harmonization of patients' results. Such a calibrator has now been identified—CRM 470— after making the appropriate dilution (8). Phase II of the study will involve the use of the common calibrator to demonstrate the lack of discrepancy among the various assays in freshly collected patient samples.

In addition to establishing clinical cut points for risk assessment, the AHA/CDC expert panel chose milligrams per liter as the unit of choice for reporting results (9) (Table 3). It is imperative that CRP values be reported in a single consistent unit. If some laboratories report CRP concentration in milligrams per liter and others in milligrams per deciliter, confusion will exist in the medical community in terms of interpreting this marker, and patients will be misclassified and mismanaged. It is the responsibility of laboratorians to provide and clinicians to demand such consistence of measurement nomenclature.

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