Why insert the capillary end into the clay during PCV?

• A. To seal the capillary tube in the clay for centrifugation.
• B. To prevent blood from clotting in the tube.
• C. To calibrate the clay.
• D. To mark the sample.

Answer: (A)

Sealing the capillary with clay creates a tight stopper at the end of the tube, which is essential for centrifugation. When the capillary is spun, the blood needs to stay inside the tube and form a clean, distinct interface between packed red cells and plasma. Without a seal, the blood could leak out or air could enter, which would disturb the separation and make the hematocrit reading unreliable. The clay plug simply provides a secure seal for the centrifugation process, not for preventing clotting or for calibration or marking.