Which test would be most useful for assessing oxygen transport in the blood?

The hemoglobin test is the most useful for assessing oxygen transport in the blood because hemoglobin is the primary protein in red blood cells that binds to oxygen in the lungs and carries it throughout the body. Monitoring hemoglobin levels provides direct insight into the blood’s capacity to transport oxygen. Low levels can indicate anemia, which compromises oxygen delivery to tissues, while elevated levels may be seen in conditions like polycythemia, where the body produces an excess of red blood cells.

Other tests listed serve different purposes. The electrocardiogram (ECG) evaluates the electrical activity of the heart, which is important for diagnosing heart-related issues but doesn't measure oxygen transport directly. A complete blood count (CBC) provides information about various components of blood, including red blood cells and hemoglobin levels, but it is a broader analysis than what is specifically needed to assess oxygen transport. Glycated hemoglobin (HbA1c) reflects average blood sugar levels over time and is primarily used in managing diabetes, not in assessing oxygen transport. Therefore, the hemoglobin test remains the most relevant choice for evaluating how well oxygen is being carried in the bloodstream.