Heparin plasma sampling as an alternative to EDTA for BNP determination on the Access-Beckman Coulter--effect of storage at -20 degrees C.

To determine BNP, EDTA plasma is the only suitable specimen recommended by the manufacturer. Since many laboratories, especially in Europe, use heparin plasma rather than EDTA plasma for many or most of their clinical assays and in particular for determination of cardiac markers (cTnI, myoglobin), it appeared critical to evaluate the use of heparin plasma samples, in comparison to EDTA plasma, for BNP determination on a automated immunochemiluminescent analyzer. The aim of this study was first, to evaluate the use of heparin plasma samples for Biosite BNP testing on the Beckman Coulter Access Immunoassay System (n=88) and second, to evaluate the effect of storage at -20 degrees C, without protease inhibitors, on the Biosite BNP assay. We obtained acceptable imprecision results with CVs ranging from 1.7 to 11.7% regardless of the anticoagulant used. The linearity of EDTA samples was good and comparable to the results observed with heparin plasma. The concentration of BNP was categorized according to the classification of the New York Heart Association (NYHA). With EDTA fresh samples as reference anticoagulant, 90% vs. 89% of subjects were classified as "concordant" with heparin fresh vs heparin frozen plasma samples, respectively. After storage at -20 degrees C, only 86% of the values of EDTA frozen were concordant with values of EDTA fresh. No subject varied by two NYHA classes. Heparin plasma is an attractive alternative to the established EDTA samples which can be used for BNP determination. This flexibility allows the simultaneous determination of CK, CK-MB, cTnI and BNP on a single heparin specimen, which facilitates blood collection for clinicians and nursing staff in an emergency unit. In addition, our results suggest that BNP could be stored at -20 degrees C for at least one month in order to perform retrospective studies.