Increasing the concentration of heparin in an ABG sample tends to cause which combination of effects?

• A. Increase pCO2 and pH, decrease pO2
• B. Decrease pCO2 and pH, increase pO2
• C. No change in pCO2, pH, or pO2
• D. Increase pCO2 and pO2, decrease pH

Answer: (A)

Increasing the concentration of heparin in an ABG sample mainly causes a dilution of the blood. This dilution lowers the amount of dissolved oxygen, so pO2 tends to decrease. Hydrogen ions are also diluted, which shifts the measured pH upward (more basic). The CO2 measurement in a diluted sample can be affected by the reduced buffering capacity and gas solubility, often resulting in a higher reported pCO2. So the overall pattern you’d expect from excess heparin is pCO2 up, pH up, and pO2 down, reflecting a dilutional preanalytic artifact rather than a true physiologic change.