For patients with respiratory disease, oxygen-carrying capabilities should be assessed by...

• A. PCV
• B. SpO2
• C. PaO2
• D. Hemoglobin

Answer: (A)

Oxygen-carrying capacity hinges on how much hemoglobin is present to bind and transport oxygen. Packed cell volume reflects the proportion of blood that is red cells, so it serves as a direct estimate of red cell mass and thus the total amount of hemoglobin available for oxygen transport. If this value is low, the blood’s capacity to carry oxygen drops even when oxygen is being delivered to the lungs normally. SpO2 shows how saturated the Hb is with oxygen, not how much Hb is around to carry it. PaO2 measures dissolved oxygen in plasma, again not the carrying capacity. Hemoglobin level would be a direct measure of the carrier, but among the given options, packed cell volume best indicates the oxygen-carrying capacity because it mirrors the red cell mass that contains the Hb needed to transport oxygen.