LAUSR

To the Editor: In terms of screening for platelet disorder, bleeding time (BT) is the current test for evaluation of platelet function. The modified Ivy method can evaluate the interaction of platelets, von Willebrand factor (vWF), subendothelium, and other platelet function disorders after blood vessel disruption using a lancet. The BT is a patient-operator dependent procedure. A specially trained technician performs the modified Ivy method at the bedside; therefore the BT is not routinely available 24 hours. Stress is present on parents, patients and technicians as they attempt to restrain the child during the test and until bleeding spontaneously stops. As mentioned by Bevan et al1, it is an invasive test that leads to an uncomfortable emotion for children. The PFA-200 is an instrument with 2 test cartridge system that evaluates platelet function and interaction with vWF. Citrated whole blood is applied to a test cartridge that contains a collagen-coated membrane and either epinephrine (Col/Epi) or adenosine diphosphate (Col/ADP).2,3 The PFA200 has been used to detect acquired and congenital platelet dysfunctions4,5 and to screen for von Willebrand disease (vWD) in adults. The 2 test cartridge system was developed to differentiate between the effects of nonsteroidal anti-inflammatory drugs6,7 and other types of qualitative defects in platelets. In this study we compared the performance of the PFA-200 to the BT as a test for platelet dysfunction. There are practical advantages of PFA-200 over BT. It is a point of care device. Citrated whole blood can be stored up to 4 hours postcollection. No specially trained technicians are required to perform the PFA200, thus improving the test’s availability. Finally, usage of the PFA-200 should eliminate the need to perform a traumatic, not highly precise and invasive test in children. This prospective diagnostic test study was conducted at King Chulalongkorn Memorial Hospital during 2017-2019. Children, age ranging from 6 months to 18 years, were sent to undergo BT together with other routine blood test. The authors used the residual sample, about 1.6mL, to perform PFA200. We obtained approval from the Institutional Review Board, Faculty of Medicine, Chulalongkorn University (IRB No. 357/61) to perform testing on residual blood, the amount that was in excess of what is required for tests ordered by each patient’s physician. Written informed consent was obtained from participants and/or their guardians before the study. We excluded patients whose platelet counts were <100,000/μL and those with hematocrit level <25% or >50%. BT were performed by a modified Ivy technique with a lancet. For purpose of standardization, in this study, all tests were by a specially trained technician. A total of 97 children who were sent to undergo BT and hemostatic workup were recruited. The mean age was 9.14±4.35 years. Children with congenital platelet disorders including vWD and Glanzmann thrombasthenia and those who were aspirin users represented the platelet dysfunction group and all of the patients in this group were confirmed to have platelet dysfunction by the gold standard test, platelet aggregation test. For subjects in the normal group, most of them were sent to our study for preoperative evaluation. Clinical characteristics of the study population were shown in Table 1. We compared the performance of the PFA-200 with the BT for the detection of combined platelet and vWF abnormalities. If either or both TABLE 1. Characteristics of the Participants