Wu, Eugene Y., Khalid W. Barazanji, and Robert L. Johnson, Jr. Sources of error in A-aD_O2 calculated from blood stored in plastic and glass syringes. J. Appl. Physiol. 82(1): 196-202, 1997.We studied the effects of time delay on blood gases, pH, and base excess in blood stored in glass and plastic syringes on ice and the effects of resulting errors on calculated alveolar-to-arterial PO₂ difference (A-aD_O2). Matched samples of dog whole blood were tonometered with gas mixtures of 5% CO₂-12% O₂-83% N₂ (mixture A), 10% CO₂-5% O₂-85% N₂ (mixture B), and 2.88% CO₂-4% O₂-93.12% N₂ (mixture C). Tonometered blood samples were transferred to 5-ml glass (5G), 5-ml plastic (5P), and 3-ml plastic (3P) syringes and stored on ice. Blood gases were measured every 1 h up to 6 h. In 5G, PO₂ progressively decreased in blood tonometered with mixture A but rose in blood tonometered with mixtures B and C. O₂ saturation progressively fell in all cases. In 5G, blood PCO₂ progressively rose regardless of which gas mixture was used, and pH as well as base excess progressively fell. The rise in PO₂ was faster in plastic than in glass syringes, and O₂ saturation always rose in plastic syringes. Differences between storage in plastic and glass syringes on PO₂ change were greatest when initial blood PO₂ was highest (mixture A). At the highest PO₂, O₂ exchange was faster in 3P than in 5P. The rise of PCO₂ was just as fast in plastic as in glass syringes, but in both the rise in PCO₂ was faster at a higher initial PCO₂ (mixture B) than at lower initial PCO₂ (mixtures B and C). Rates of PO₂ and PCO₂ change in matched samples were significantly faster in 3P than in 5P. Errors due to rises in PCO₂ and PO₂ cause additive errors in calculated A-aD_O2, and when blood is stored in plastic syringes for >1 h significant errors result. Errors are greater in normoxic blood, in which estimated A-aD_O2 decreased by >10 Torr after 6 h on ice in plastic syringes, than in hypoxic blood.