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To the Editor:
A standardized procedure for specimen collection is essential to achieve accurate and reliable coagulation measurements (1). Efforts have been made to identify the most suitable procedures for collecting, handling, and storing specimens for coagulation testing (2-6), including a recommendation that samples be centrifuged at room temperature (7). There is no definitive evidence, however, that centrifugation at alternative temperatures might significantly influence results of coagulation testing.
A single practiced phlebotomist collected blood from 12 healthy volunteers and 13 consecutive patients on oral anticoagulant therapy directly into three 4.5-mL siliconized evacuated tubes containing 0.5 mL of 0.105 mol/L buffered trisodium citrate (Becton Dickinson), using a 20-gauge, 0.80 ÷ 19 mm Venoject® multisample straight needle (Terumo Europe NV). Venipunctures were performed in the morning of the same day on fasting patients, who had given explicit informed consent. Tourniquet placement was <20 s, and all tubes were from the same lot. Venous accesses were straightforward in all cases, and no hemolyzed or lipemic specimens were encountered.
The tubes from each patient were gently mixed, pooled, and finally divided into 3 identical 4-mL aliquots. The 3 aliquots were centrifuged at 1500g for 10 min at 4 °C, 12 °C, or room temperature (21 °C). We performed the 3 centrifugation procedures sequentially on the same centrifuge (Varifuge 3.2RS; Heraeus Instruments) and verified the effective correspondence between theoretical and operative temperatures.
After centrifugation, plasma was separated and immediately analyzed. Activated partial thromboplastin time (aPTT), prothrombin time...