What lab value is considered the gold standard for measuring oxygenation?

The gold standard for measuring oxygenation is the arterial oxygen partial pressure, known as PaO2. This is a direct measurement obtained through arterial blood gas analysis, reflecting the amount of oxygen dissolved in plasma and providing an accurate assessment of a patient’s oxygenation status. This measurement is crucial for determining how well oxygen is being delivered to the body’s tissues.

While SpO2, which represents peripheral capillary oxygen saturation as measured by pulse oximetry, is a commonly used non-invasive method to estimate blood oxygen levels, it is not as precise as the direct measurement from arterial blood. Factors such as low perfusion, the presence of carbon monoxide, or other physiological conditions can lead to discrepancies between SpO2 and actual oxygenation levels.

SaO2 refers to the oxygen saturation of hemoglobin in the blood but is also typically determined via arterial blood gas analysis. Although an important value, it is often reported alongside PaO2.

FIO2 represents the fraction of inspired oxygen, which indicates the percentage or concentration of oxygen being delivered to a patient, but it does not directly measure the oxygenation status of the blood.

Overall, while SpO2 provides quick insights into oxygenation and is widely used in clinical settings, the PaO