Can Whole-Blood Samples Be Stored over 24 Hours without Compromising Stability of C-Reactive Protein, Retinol, Ferritin, Folic Acid, and Fatty Acids in Epidemiologic Research?

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Abstract
Ideally, blood samples for biomarker measurement are collected centrally and processed immediately to avoid any unwanted changes in concentrations that could affect validity. In large-scale epidemiologic and clinical studies, however, this theoretical goal must give way to a more pragmatic approach (1, 2). The Amsterdam Born Children and their Development (ABCD) study is a clinically based cohort study of pregnant women in Amsterdam (The Netherlands) in which we use, for practical and ethical reasons, blood collection in conjunction with existing schemes of care, with samples subsequently sent to a central laboratory by mail or courier. As a consequence, delay times between collection and processing may exceed 24 h, to an incidental maximum of 96 h. Although the stabilities of the biomarkers of interest, i.e., C-reactive protein (CRP), retinol, ferritin, folic acid, and fatty acids (FAs), have been studied previously (1-9), the variety of designs (e.g., storage Յ24 h) hampers the applicability of existing results to our research and similar studies. We therefore investigated the appropriateness of our standardized, practice-based approach of blood collection by assessing stability in samples stored up to 96 h (the maximum delay time possible when samples are sent by mail) with a focus on the first 28 h (the maximum delay time allowed in the ABCD study). Blood samples were collected from 41 generally healthy female volunteers, 22-56 years of age. One woman was at that time 16 weeks pregnant, but because her measurements did not deviate, we decided not to exclude her from analysis. Written informed consent was obtained from all participants. For 20 women, 28 mL of blood was collected in seven 4-mL Vacuettes (Greiner BV) for the preparation of serum. For the other 21 women, 28 mL of blood was collected in seven 4-mL Vacutainer EDTA tubes (Becton and Dickinson BV) for the preparation of plasma. One tube from each woman was centrifuged (1600g for 10 min) between 1 and 2 h after blood collection (t 0 ; baseline), and the remaining tubes were stored in a cabinet at room temperature (ϳ21 °C) and centrifuged 2 (t 2), 4 (t 4), 24 (t 24), 26 (t 26), 28 (t 28), or 96 (t 96) h after baseline. Time points were chosen to mimic courier and postal conditions seen in the ABCD study, 4 h being the anticipated maximum delay time when blood is sent by courier, 28 h being the anticipated maximum delay time when blood is sent by

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