How do you safely aliquot serum from a clotted whole blood sample without disturbing the clot?

• A. Allow adequate clotting, centrifuge to separate serum, then carefully aspirate supernatant with a clean pipette avoiding disturbance of the clot.
• B. Vortex the sample to release serum from the clot.
• C. Decant serum without centrifugation.
• D. Remove serum before clot forms.

Answer: (A)

The method hinges on proper serum separation: let the blood fully clot, then use centrifugation to pull the liquid serum away from the clot, and finally aspirate only the clear serum from the top with a clean pipette, without disturbing the clot. Centrifugation creates a distinct interface between the clot and the liquid, so you can remove the serum cleanly and minimize contamination from cells or clotting factors that could affect test results. Using a fresh, sterile pipette tip and avoiding suction near the clot helps keep the clot intact and prevents disturbing it.

Vortexing would mix the clot with serum and disrupt the solid clot components, leading to contamination and unreliable results. Decanting without centrifugation won’t provide a clean separation of serum from the clot and can still pull clot fragments or fibrin into the aliquot. Attempting to remove serum before the clot forms is impossible because serum is the liquid portion that remains after coagulation; before clotting, you have whole blood, not serum.