Which anticoagulant is commonly used for complete blood count (CBC) samples?

• A. Citrate.
• B. Heparin.
• C. EDTA is commonly used for CBC.
• D. Fluoride.

Answer: (C)

For CBC samples, you need an anticoagulant that keeps blood from clotting while preserving the cells’ integrity for accurate counts and morphology. Ethylenediaminetetraacetic acid (EDTA) does just that by binding calcium, which is essential for coagulation, so the blood stays liquid and the red cells, white cells, and platelets remain well preserved. That’s why EDTA is standard and is the additive in the common lavender/purple-top tubes used for CBC.

Citrate is mainly for coagulation testing because it’s used to study clotting times and can alter cell morphology if used for CBC. Heparin is useful for some plasma-based tests but can affect certain CBC measurements and cell morphology, making it less ideal for routine counts. Fluoride is used to inhibit glycolysis for glucose tests, not for CBC.

So EDTA is the go-to anticoagulant for CBC due to its strong calcium chelation that prevents clotting while maintaining cell integrity.