Use of the PFA-100 in the assessment of primary, platelet-related hemostasis in a pediatric setting.

The platelet function analyzer, PFA-100, has been designed to provide an in vitro measure of primary hemostasis simply, quickly, quantitatively, and accurately to aid in the routine screening of patients with potential hemorrhagic risk due to abnormal platelet plug formation. The system measures the closure time (CT), or the time taken for platelets in a sample of anticoagulated blood to form a plug that occludes a microscopic aperture cut into a membrane coated with collagen and either epinephrine or ADP. The high shear stresses produced in the analyzer lead to platelet plug formation that is greatly dependent on von Willebrand's factor (vWF). In this article, we detail the system itself and describe our initial studies using the PFA-100 to assess primary hemostasis in pediatric populations. Normal ranges have been established for healthy children and neonates. CTs for healthy children are independent of the needle gauge (21G or 23G) used for blood sampling. They are similar to CTs for healthy adults, but neonates have significantly shorter CTs, likely due to increased levels of vWF. Children with hemophilia have normal CTs, whereas seven out of eight patients with von Willebrand's disease (vWD) have abnormally long CTs. CT reproducibility between duplicate samples is excellent. Our preliminary results indicate that the PFA-100 will be useful in the evaluation of primary hemostasis in children, as well as in adults.