Which test measures the percentage of erythrocytes in a volume of blood?

• A. Fecal occult blood test
• B. Hematocrit (Hct)
• C. Laryngoscopy
• D. Glucose tolerance test

Answer: (B)

The main idea is understanding what hematocrit measures: the proportion of blood volume made up by red blood cells. When a blood sample is spun in a centrifuge, plasma sits on top, a thin layer of white cells and platelets forms, and the bottom bulk is the packed erythrocytes. Hematocrit is the height or volume of that red cell layer expressed as a percentage of the total sample volume. This directly tells you how much of the blood is rbc by volume, which is why it’s used to assess red cell mass and volume status.

A high hematocrit can indicate more red cells relative to plasma, as in dehydration or polycythemia; a low hematocrit points to fewer red cells, as in anemia, blood loss, or overhydration. It’s often part of a complete blood count and is related to hemoglobin concentration and RBC count, with rough relationship Hb ≈ hematocrit × 3.

The other tests measure different things: a fecal occult blood test looks for hidden blood in stool; laryngoscopy examines the larynx and vocal cords; a glucose tolerance test assesses how the body handles glucose.