One of the principal utilities of arterial blood gas (ABG) analysis is to help assess blood oxygenation status. The two ABG parameters used for this assessment are pO₂(a) (partial pressure of oxygen in arterial blood) and sO₂(a) (% of total hemoglobin that is saturated with oxygen). In health pO₂(a) is maintained within the range 10.6-13.3 kPa (80-100 mmHg) and hypoxemia (reduced blood oxygen) is diagnosed if pO₂(a) is less than 10.6 kPa (80 mmHg). The purpose of this article is to highlight the spurious severe hypoxemia that occurs in patients with particularly high white-cell count or high platelet count. In these patients there is a marked discrepancy between measured (in vitro) pO₂(a) and true (in vivo) pO₂(a). The article will address the supposed mechanism that gives rise to spurious hypoxemia and the ways in which it can be identified. Some representative case histories will be presented which serve to show that failure to recognize spurious hypoxemia can lead to needless investigation and inappropriate intervention, including assisted ventilation. The article begins with a brief overview of the significance of pO₂(a) and sO₂(a) for assessment of blood oxygenation.

Approx. reference intervals: 
pO₂(a) on room air     10.6-13.3 kPa (80-100 mmHg)
sO₂(a) on room air     96-98 %
White-cell count         4.0-11.0 × 10⁹/L (4.0-11 × 10³/µL)
Platelet count             150-400 × 10⁹/L (150-400 × 10³/µL)