Which factor most significantly affects ABG results if not properly controlled?

• A. The patient's hair color
• B. Time of day
• C. The sample temperature during handling
• D. Room lighting

Answer: (C)

Temperature of the blood sample during handling is the most influential factor because arterial blood gas values depend on chemical equilibria that shift with temperature. CO2 exists in equilibrium with carbonic acid and bicarbonate, and the hydrogen ion concentration sets the pH; both of these are temperature dependent. If the specimen is not kept at the correct temperature, CO2 can diffuse into or out of the sample and pH can drift, causing inaccurate PaCO2 and pH readings (and thus miscalculated HCO3). That’s why controlling sample temperature and analyzing promptly are essential for reliable ABG results. The other factors—hair color, time of day, room lighting—do not meaningfully affect the blood gas measurements.