Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

Why is a hematocrit test ordered?

1. Determine the relative volume of RBCs to plasma

2. Check the patient's hemoglobin when anemia is suspected

3. Check the Rh factor in pregnant women

4. Determine the clotting ability of the patient's blood

The correct answer is: Determine the relative volume of RBCs to plasma

A hematocrit test is primarily ordered to determine the relative volume of red blood cells (RBCs) in relation to the total blood volume. This measurement is vital for assessing various physiological and pathological conditions. A low hematocrit can indicate conditions such as anemia, where there is a decreased number of red blood cells, while a high hematocrit can suggest dehydration or polycythemia, where there is an increased concentration of red cells. While the other options relate to important aspects of blood analysis, they do not accurately represent the primary purpose of the hematocrit test. For example, checking hemoglobin levels is a distinct test often conducted alongside hematocrit but serves a different function. Determining the Rh factor is critical during pregnancy and is usually assessed through different blood testing methods. Evaluating the clotting ability of blood involves tests such as prothrombin time or activated partial thromboplastin time, which again, are separate from the hematocrit measurement. Hence, identifying the relative volume of RBCs to plasma is the central aim of conducting a hematocrit test.