The present invention relates to a reconstitution solution for spray dried plasma having a non-anticoagulant compound that does not bind calcium. When the reconstitution solution of the present invention is mixed with spray dry plasma, the reconstituted plasma mediates platelet adhesion and aggregation about the same as or greater than the starting plasma prior to spray drying. The present invention also relates to an assay for determining platelet adhesion and aggregation using microfluidic flow cell system having a shear flow. The assay assesses labeled whole blood samples having reconstituted plasma having spray dried plasma and a reconstitution solution; platelets; and red blood cells. After inducing a shear flow under conditions suitable for clot formation, coverage area of the platelets, intensity of the platelets, morphology, or a combination thereof is detected to determine platelet accumulation (e.g., platelet adhesion and aggregation).