A comparison of venous blood gas analysis with paired specimens collected in syringes and evacuated blood collection tubes.

Abstract Background Venous blood samples collected in evacuated blood collection tubes are generally not considered suitable for measurement of oxygenation status. However, whether pH, pCO2 and HCO3- results from venous blood samples collected in evacuated tubes are reliable remains unclear. Methods Paired samples were collected from 38 healthy volunteers using 2 collection methods: 1) collection of blood directly into a blood gas syringe and 2) collection of blood into an evacuated tube with subsequent anaerobic transfer into a blood gas syringe. Samples were analyzed for pH, pCO2, HCO3-, and pO2. Results Samples collected in evacuated tubes showed significant positive mean biases of 0.03 and 7.5 mmHg for pH and pO2, respectively, and significant negative mean biases of 5.0 mmHg and 1.2 mmol/l for pCO2 and HCO3-, respectively. Collection in evacuated tubes resulted in biases exceeding the total allowable errors in 16%, 40%, 21% of samples for pH, pCO2, HCO3-, respectively, when compared to samples collected in syringes directly. Conclusions Samples for venous blood gas analysis should be collected directly into blood gas syringes for accurate assessment of ventilation and/or acid-base status. Biases observed for samples collected in evacuated tubes are consistent with air contamination and/or vacuum effects.