Microfluidic assay of hemophilic blood clotting: Distinct deficits in platelet and fibrin deposition at low factor levels

Summary Background Coagulation factor deficiencies create a range of bleeding phenotypes. Microfluidic devices offer controlled hemodynamics and defined procoagulant triggers for measurement of clotting under flow. Objectives We tested a flow assay of contact pathway-triggered clotting to quantify platelet and fibrin deposition distal of dysfunctional thrombin production. Microfluidic metrics were then compared with PTT or % factor activity assays. Methods Whole blood (WB) treated with low level corn trypsin inhibitor (4 μg mL−1) from nine healthy donors and 27 patients (deficient in factor [F] VIII, 19 patients; FIX, one patient; FXI, one patient; VWF, six patients) was perfused over fibrillar collagen at wall shear rate = 100 s−1. Results Using healthy WB, platelets deposited within 30 s, while fibrin appeared within 6 min. Compared with healthy controls, WB from patients displayed a 50% reduction in platelet deposition only at  40 s). Full occlusion of the 60-μm high channel was completely absent over the 15-min test in patients with  1% factor. Conclusion Spontaneous bleeding in patients with  1% activity (PTT of ~40–60 s), a level that does not necessarily rescue fibrin formation under flow.