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Licensed Unlicensed Requires Authentication Published by De Gruyter September 21, 2011

Long-term stability of endogenous B-type natriuretic peptide (BNP) and amino terminal proBNP (NT-proBNP) in frozen plasma samples

Thomas Mueller, Alfons Gegenhuber, Benjamin Dieplinger, Werner Poelz and Meinhard Haltmayer


The aim of the present study was to assess the long-term stability of endogenous B-type natriuretic peptide (BNP) and amino terminal proBNP (NT-proBNP) in plasma samples stored at –20°C without addition of protease inhibitors (e.g., aprotinin). Stability of BNP and NT-proBNP was tested in 60 EDTA plasma samples with BNP values between 30 and 420 pg/ml. Initial BNP and NT-proBNP plasma concentrations were determined within four hours after blood collection using the AxSYM BNP and the Elecsys NT-proBNP assays. Subsequently, all samples were stored at –20°C and were thawed for the second BNP and NT-proBNP determination on the two instruments after one day, 30 days, 60 days, 90 days and 120 days, respectively. Mean recovery (i.e., residual immunoreactivity) of BNP and NT-proBNP expressed in percent of the initial value for the given time interval of storage was calculated. Mean recovery of BNP was less than 70% after one day of storage at –20°C and decreased to less than 50% after two to four months of storage (e.g., recovery of endogenous BNP after three months of storage at –20°C ranging from 0% to 71%). In contrast, mean recovery of NT-proBNP was generally greater than 90%, irrespective of the duration of storage at –20°C (e.g., recovery of endogenous NT-proBNP after three months of storage at –20°C ranging from 91% to 112%). In conclusion, the determination of endogenous BNP with the AxSYM assay using frozen plasma samples may not be valid under the conditions tested. In contrast, NT-proBNP as measured by the Elecsys assay may be stored at –20°C for at least four months without a relevant loss of the immunoreactive analyte.

Corresponding author: Meinhard Haltmayer, Department of Laboratory Medicine, Konventhospital Barmherzige Brueder, Seilerstaette 2, 4021 Linz, Austria. Phone: +43-732-7897-2201, Fax: +43-732-7897-2299, E-mail:


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Received: 2004-2-23
Accepted: 2004-4-27
Published Online: 2011-9-21
Published in Print: 2004-8-1

© Walter de Gruyter

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