Which method directly measures levels of oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin, and methemoglobin?

Hemoximetry is the correct method for directly measuring levels of oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin, and methemoglobin. This technique involves using a specialized device known as a co-oximeter, which can analyze a blood sample to provide a detailed breakdown of the different forms of hemoglobin present.

In clinical practice, hemoximetry is particularly valuable because it allows for a precise understanding of a patient's oxygen-carrying capacity and the presence of abnormal forms of hemoglobin that can interfere with oxygen transport and utilization. This is critical in situations where a patient may have carbon monoxide exposure or specific conditions that lead to methemoglobinemia.

Other methods, like pulse oximetry, primarily measure only the saturation of oxyhemoglobin and do not differentiate between other hemoglobin species. Capnography measures carbon dioxide levels and ventilation status rather than hemoglobin composition, while a ventilation-perfusion scan assesses airflow in the lungs versus blood flow and is not directly related to hemoglobin analysis. Thus, hemoximetry stands out as the method specifically designed for detailed hemoglobin evaluation.