Question

Which anticoagulant is used as choice for CBC investigations?

• A. 3.8% trisodium citrate
• B. EDTA
• C. Double oxalate mixture
• D. All of these

Answer 1

Answer:

B. EDTA

Primary Anticoagulant for CBC

• EDTA (Ethylenediaminetetraacetic acid) is the preferred anticoagulant for Complete Blood Count (CBC) and other hematological investigations.
• It is commonly available in the form of Dipotassium salt (K2EDTA) or Tripotassium salt (K3EDTA).
• Mechanism of Action: EDTA functions by chelating (binding) calcium ions in the blood, which is essential for the coagulation cascade, thereby preventing clotting.

Key Advantages

• Cell Morphology Preservation: EDTA is superior in preserving the shape and structure of blood cells (RBCs, WBCs, and platelets), making it ideal for the examination of blood films and manual differential counts.
• Platelet Stability: It effectively prevents platelet aggregation, ensuring accurate platelet counts.
• Staining Quality: Blood smears prepared from EDTA-anticoagulated samples provide high-quality staining results (e.g., Leishman stain or Giemsa stain).

Clinical Considerations

• Tube Color: Blood collection tubes containing EDTA are typically identified by a lavender or purple color-coded cap.
• Limitations: While excellent for hematology, EDTA is unsuitable for coagulation studies (like PT/APTT) because it inhibits the calcium-dependent coagulation factors. It also alters calcium and iron levels, rendering it invalid for biochemical assays involving these elements.
• Concentration: The standard concentration used is approximately 1.5 mg per mL of whole blood. Excessive amounts of EDTA can cause red blood cell shrinkage (crenation), while insufficient amounts may lead to micro-clots.