Methodical Approach to Collecting and Preserving Plasma Samples Containing B-Type Natriuretic Peptide

Sir, We have read the comments raised by Hazukova and Colleagues on the method used for collecting and preserving the plasma samples containing B-type natriuretic peptide (BNP), which we described in a paper recently published in this Journal 1. The method we used is not an original one, since the number of articles that have used it so far is not negligible 234567. BNP is a widely used tool for managing heart failure patients from the diagnostic, therapeutic and prognostic points of view. Therefore, we strongly agree on the need to have stringent methodological criteria in order to obtain reliable and applicable results. In the clinical setting, applicability of a measurement is important. This is, for example, the case for the time during which we and others, maintained the patients in a supine position before collecting the blood samples. Although at least 60–100 min could be considered ideal, from the practical point of view this time is so long that it would strongly limit the applicability of BNP evaluation in clinical practice. This is why, in our research we tried to minimize these problems by using a standard time of rest before sample collection. Data regarding stability of BNP and related peptides are sparse and conflicting. The usage of stabilizing agents has been suggested in several studies that have validated the diagnostic and prognostic values of BNP and NT-proBNP 8 and has also been recently recommended by the IFCC Committee on standardization of markers of cardiac damage 7. On the basis of these reports, our results and the interesting considerations made by Hazukova and Colleagues, we can only say that the blood sample storage used so far has not limited the prognostic information carried by BNP in our series. As far as the time to analysis is concerned, we are happy to provide more information on the protocol we used. The baseline and the one month samples for each patient were analysed using the same kit. Since one kit was used for analysing more than two samples, the mean time to analysis was 10 months. We tested the hypothesis that time could influence the results but we did not find any significant difference in the BNP plasma levels related to the time between collection and analysis. We found the comments of Hazukova and Colleagues of great interest and very helpful in showing that although considering the limitations of the method used so far, BNP evaluation has relevant prognostic information in our study as well as in previously published studies.