Which specimen is needed to accurately measure blood gases?

To accurately measure blood gases, an arterial blood gas (ABG) sample is necessary. This type of sample is drawn directly from an artery, typically the radial or femoral artery, and provides crucial information about the levels of oxygen and carbon dioxide in the blood, as well as the blood's pH. These measurements are essential for assessing respiratory function and determining how well oxygen is being delivered to tissues, along with the effectiveness of the lungs in excreting carbon dioxide.

In contrast, a urine sample does not provide information on blood gas levels, as it reflects renal function and metabolic waste rather than respiratory gas exchange. A venous blood sample, while useful for many tests, is not reliable for measuring blood gases, as it predominantly reflects mixed venous blood returning to the heart, which has already undergone gas exchange in the tissues. Saliva, similarly, does not offer any relevant data regarding blood gases and is mainly used for other types of analyses, such as hormone levels or bacterial detection. Therefore, the arterial blood gas sample is the gold standard for direct measurement of blood gases in clinical practice.