The buffy coat layer in a hematocrit tube represents the concentration of which cells?

• A. Red blood cells
• B. White blood cells
• C. Platelets
• D. Plasma cells

Answer: (B)

During centrifugation, blood separates by density into distinct layers: a top plasma layer, a thin middle buffy coat, and a bottom red blood cell layer. The buffy coat is the leukocyte-rich portion that sits between plasma and red cells and also contains platelets. When asked which cells are represented by this middle layer, the main cell type associated with the buffy coat is white blood cells. Platelets are present in that layer as fragments, not full cells, so the focus for this question is on leukocytes.