Converting waste into value. Stability of leftover EDTA whole blood: serum vs. plasma for nine clinical chemistry analyses

This study evaluates the utility of leftover EDTA whole blood from a diagnostic biobank for determining concentrations of ferritin, cobalamin, homocysteine, hCG, and thyroid-related hormones and antibodies (TSH, fT4, fT3, TRAb, and anti-TPO). Twenty participants were included. Pre-analytical bias in their blood samples was assessed as per European Federation of Clinical Chemistry and Laboratory Medicine Milano performance specifications. We evaluated the stability of EDTA whole blood stored at various intervals (days 0, 1, 6, and 13), and compared plasma derived from these samples with serum samples. Bland Altman plots and Paired t-test were used to identify statistically significant differences. We found good quantitative agreement, with biases within set performance specifications for cobalamin (14%), fT4 (3.5%), fT3 (3.6%), TSH (15%), and ferritin (7.4%). The calculated biases for serum vs. EDTA plasma day 6 were as follows: cobalamin 1.9%, fT4 2.6%, fT3 0.4%, TSH −2.1%, and ferritin −4.5%. The biases for homocysteine exceeded limits in all comparisons, except serum vs. EDTA plasma on day 0 and between EDTA plasma from day 0 and day 1. The calculated bias of 41% exceeded the set limit of 13% when comparing serum with EDTA plasma day 6. For hCG, anti-TPO, and TRAb, limited measurable levels restricted bias calculations. As per the diagnostic biobank protocols, EDTA blood stored for up to 6 days provides plasma suitable for analyzing cobalamin, fT4, fT3, TSH, and ferritin. Our study confirms previous findings that homocysteine has poor stability in whole blood.