Whole Blood Lumiaggregation: Evaluation of Reagents

We evaluated the whole blood lumiaggregation system, which analyzed the optimal sample dilutions and ago nist concentrations. We also showed that platelet aggregation using the whole blood impedance technique, as compared to the platelet-rich plasma optical method, yielded similar informa tion. In the extension of that study, we further evaluated the stability of the reagents used in platelet aggregation. The most commonly used agonists thrombin, ristocetin, arachidonic acid, adenosine diphosphate, and collagen were monitored over a 1-year period. Throughout the entire period, aliquots of the reconstituted reagents were stored at -20°C, -50°C, and -70°C, with the exception for collagen, which was kept at 4°C. Every 2 weeks tests were performed using the whole blood from the same healthy volunteer. Platelet aggregation and aden osine diphosphate release were measured after stimulation with 1.0 U/mL thrombin, 1.0 mg/mL ristocetin, 0.5 mM arachidonic acid, 10 μM adenosine diphosphate or 3 μg/mL collagen. The results indicated that thrombin was stable at all temperatures over the 1-year period. Platelet agglutination with ristocetin was similar among samples for about 2 months; after that time some deterioration of ristocetin was noticed, especially at -20°C. Reconstituted arachidonic acid, frozen at -20°C, was stable for about 1 month, and at the lower temperatures this agonist was good for 4 months. On the contrary, adenosine diphosphate and collagen exhibited stability throughout the 1- year period. Based on the information provided by this study, we encourage more laboratories to use whole blood lumiaggre gation to evaluate platelet function.