Postural change during venous blood collection is a major source of bias in clinical chemistry testing

• Clinical chemistry tests were measured in different postural position.
• Hb, Ht, albumin and total proteins increased from supine to sitting.
• Hb, Ht, albumin, ALP, amylase, AST, bilirubin, calcium, total and HDL cholesterol, GGT, glucose, LDH, magnesium, proteins and triglycerides increased from sitting to standing.
• These results emphasize the need of standardizing patient's posture during phlebotomy.

BackgroundTo investigate the influence of different phlebotomy postures on clinical chemistry testing.Materials and methodsNineteen volunteers were recruited from the laboratory staff. A first set of samples was drawn after 25 min of resting in supine position, a second after 20 min in sitting position, and a third after 20 min in upright position. Clinical chemistry testing was performed on Roche Cobas C501.ResultsThe plasma volume change (PVC) was − 3.4% from supine to sitting, − 14.1% from supine to standing and − 9.7% from sitting to standing. Compared to quality specifications for bias, hemoglobin, hematocrit, albumin and total proteins exhibited meaningful increases from supine to sitting, whereas meaningful increases were observed for hemoglobin, hematocrit, albumin, alkaline phosphatase (ALP), amylase, aspartate aminotransferase (AST), total bilirubin, calcium, total and high-density lipoprotein (HDL) cholesterol, gamma-glutamyl transferase (GGT), glucose, lactate dehydrogenase (LDH), magnesium, total protein and triglycerides from sitting to standing. The parameters with meaningful bias from sitting to upright were hemoglobin, hematocrit, albumin, ALP, total bilirubin, calcium, total and HDL cholesterol, glucose, LDH and total protein.ConclusionsThese results provide further support to the need of standardizing patient's posture during phlebotomy.