For routine coagulation testing, which anticoagulant is preferred to ensure accurate results?

• A. Sodium Citrate
• B. EDTA
• C. Heparin
• D. Potassium Oxalate

Answer: (A)

Sodium citrate is preferred because it preserves the plasma’s ability to form a clot by temporarily binding calcium, which keeps blood from clotting in the tube but allows clotting to be measured accurately later when calcium is added back. This reversible calcium binding creates a stable, reproducible matrix for routine clot-based tests like PT and aPTT. The standard collection uses a fixed blood-to-anticoagulant ratio (about 9:1) to avoid diluting coagulation factors or skewing results.

EDTA and potassium oxalate also chelate calcium but are not used for routine coagulation testing; EDTA is excellent for preserving cells in hematology, not for measuring clot formation, and oxalate is not suited for these tests. Heparin inhibits the clotting cascade, which can alter clotting times and reduce reliability for standard PT/aPTT measurements.