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Stability of biochemical analytes in blood specimens subjected to delayed processing

Blood is nominally centrifuged within 45 min of phlebotomy and the plasma or serum is stored at −80°C until it is analyzed, but in some off‐nominal cases, whole blood may be held at 20–25°C for an extended period after phlebotomy. The standard recommendation for the processing time was designed to maximize analyte stability. We investigated the stability of several analytes related to bone metabolism and clinical chemistry. Blood was collected from 10 subjects and was maintained at ambient temperature and protected from light for 45 min and 2.5, 5, and 24 h after phlebotomy before it was centrifuged to collect serum. Significant changes were observed for parathyroid hormone (PTH, decreased at 24 h, P < 0.05) and osteocalcin (decreased at 24 h, P < 0.001). Homocysteine was significantly elevated at 24 h (P < 0.001). No changes were observed for the remaining analytes, including calcium, cortisol, methylmalonic acid, retinol‐binding protein, total antioxidant capacity, transferrin and transferrin receptors, 25‐hydroxyvitamin D, cholesterol, triglycerides, alkaline phosphatase, total protein, sodium, albumin, creatinine, aspartate aminotransferase, and alanine aminotransferase. These studies indicate that some blood components related to bone and iron metabolism, including PTH, osteocalcin, and homocysteine, are not stable for up to 24 h when stored at 25°C. This supported by the NASA Human Research Program.