Advanced Phlebotomy Practice Test 2026 - Free Phlebotomy Certification Practice Questions and Study Guide

Arterial blood gas values are time-sensitive because the blood continues to exchange gases with the air and cells metabolize after collection. CO2 can diffuse out, pH can shift as hydrogen ions change, and oxygen tension can fall as cells use the available O2. These processes cause the measured pH, pCO2, and pO2 to drift away from the patient’s true in vivo values the longer the sample sits. To preserve accuracy, we analyze within a narrow window—typically 15–30 minutes after collection. If immediate analysis isn’t possible, refrigerate or place the sample on ice to slow changes and still aim to analyze as soon as feasible, ideally within 30 minutes. Delays of a couple hours or more lead to significant gas changes and unreliable results.