Which of the following correctly identifies the three main layers of a separated blood sample after centrifugation, and matches the primary formed elements seen on a blood smear?

• A. Buffy coat (top), erythrocytes (middle), plasma (bottom)
• B. Erythrocytes (top), plasma (middle), buffy coat (bottom)
• C. Plasma (top), buffy coat (middle, containing leukocytes and platelets), erythrocytes (bottom)
• D. Plasma (top), erythrocytes (middle), buffy coat (bottom)

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the components of blood and their densities. Blood consists mainly of plasma, erythrocytes (red blood cells), leukocytes (white blood cells), and platelets. When centrifuged, these components separate based on their density.
2. Step 2: Recall that plasma is the least dense component and will form the top layer after centrifugation. Plasma is the liquid portion of blood containing water, proteins, nutrients, and waste products.
3. Step 3: Identify the buffy coat, which is a thin middle layer composed of leukocytes and platelets. This layer is less dense than erythrocytes but more dense than plasma.
4. Step 4: Recognize that erythrocytes are the most dense formed elements and will settle at the bottom of the tube after centrifugation.
5. Step 5: Match the layers from top to bottom as plasma (top), buffy coat (middle, containing leukocytes and platelets), and erythrocytes (bottom), which corresponds to the correct identification of the three main layers and their primary formed elements.