Citrate Blood a Century of Artifact.

Sodium citrate has been used as an anticoagulant to prepare blood and fractions for over 100 years. Its use is sufficiently common that many investigators do not differentiate anticoagulated blood from blood per se. To evaluate the influence of citrate anticoagulation on the dynamics of the blood coagulation process, we compared the properties of blood, platelet rich plasma (PRP) and platelet poor plasma (PPP) prepared and stimulated using standard citrate/Ca++ reconstitution methodologies with matching samples in which transient anticoagulation without disruption of Ca++ homeostasis was achieved by blockade of the contact pathway (using corn trypsin inhibitor (CTI) or inhibitory antibodies to factor XIa). Phlebotomy blood was collected into citrate, CTI or CTI supplemented with citrate, the latter combination establishing conditions in which the effects of citrate anticoagulation in the absence of contact pathway contributions could be studied. Coagulation reactions in citrated milieus were initiated in typical fashion by Ca++ addition or following preincubation with Ca++ prior to tissue factor (Tf) addition in CTI citrate plasma; blood/products stabilized by CTI alone were initiated via Tf addition. Reaction dynamics were analysed using either calibrated automated thrombography (CAT) or thromboelastography (TEG). Platelet aggregation studies compared the reactivity of a panel of agonists. Significant differences were seen in the response of samples exposed to citrate. These results included: