Which anticoagulant is preferred for preparing blood smears to diagnose malaria?

• A. Sodium citrate
• B. EDTA
• C. Heparin
• D. Sodium fluoride

Answer: (B)

When diagnosing malaria from a blood smear, preserving the appearance of both red blood cells and the parasite is essential, and the anticoagulant used should prevent clotting without distorting cell morphology or interfering with staining. EDTA does this well: it binds calcium to stop clotting while keeping cell membranes intact, and it is compatible with Giemsa staining used to visualize Plasmodium species in thick and thin smears. Other anticoagulants can alter red cell morphology or staining quality—sodium citrate can cause dilution and shape changes, heparin can lead to staining artifacts and cell distortion, and sodium fluoride is not an adequate anticoagulant for smear preparation. Therefore, EDTA is the best choice for preparing malaria blood smears.