UCSF

Abstract Abstract 3295 Patients with abnormal bleeding are frequently referred to specialists for evaluation of bleeding diatheses. For many patients with strong clinical evidence of a bleeding disorder (positive personal and family history of bleeding), a clear diagnosis remains elusive even after exhaustive laboratory evaluation. Yet, failure to fully characterize these patients may lead to inadequate therapy and serious complications including severe anemia requiring transfusion, postpartum hemorrhage, and unnecessary surgical procedures (e.g. hysterectomy, cautery). Moreover, even in patients with a diagnosed bleeding disorder, the current testing technology is suboptimal. Platelet aggregometry, the gold standard for the diagnosis of platelet disorders, is technically cumbersome, requires a large volume of blood, and is poorly standardized. In the case of Von Willebrand disease (VWD) the current diagnostic assays have large coefficients of variation and have relatively poor reproducibility and bleeding symptoms vary greatly between patients with similar antigen levels, even within the same subtype. Therefore, there remains a need to develop assays with greater sensitivity to detect hemostatic defects and specificity for platelet dysfunction. The purpose of this study was to explore the use of perfusion chamber technology (adapted to permit real time continuous measurement of the kinetics of thrombosis) to evaluate the thrombotic process in pediatric patients with known bleeding disorders compared to normal adult controls. Thrombosis was initiated by perfusion of Factor Xa-inhibitor anti-coagulated whole blood through a collagen coated capillary at arterial (1600s−1) and venous (600s−1) shear rates. Thrombosis was measured by the rate of thrombus growth (platelet deposition over time) and endpoint thrombosis (thrombus size). Results and discussion Rate of thrombus growth (AU) Endpoint thrombosis (MFI/mm2) 600s−1 1600s−1 600s−1 1600s−1 Normal controls (n=101) 857 ± 64 1526 ± 169 378455 ± 45974 383690 ± 56030 Glanzmanns (n=2) 42 ± 13 22 ± 12 23598 ± 20063 26618 ± 1543 Low vWF (n=4) 615 ± 184 923 ± 543 280842 ± 87725 238657 ± 133115 Type 1 VWD (n=3) 802 ± 1 933 ± 463 377126 ± 16872 247719 ± 117475 Type 2A VWD (n=2) 790 ± 118 564 ± 756 357134 ± 60413 148450 ± 191337 Type 2B VWD (n=2) 140 ± 15 129 ± 34 71180 ± 6300 36471 ± 8138 Platelet dysfunction (n=4) 475 ± 176 902 ± 329 210767 ± 66440 236889 ± 82017 All data are presented as mean ± SD (limited n/patient group prevents statistical analysis). Platelet dysfunction can be identified using PCA. Clear abnormalities in rate and extent of thrombosis were demonstrated in Glanzmanns patients at both arterial and venous shear. VWD thrombotic process was altered and within individuals, correlated with severity of disease; in addition, PCA identified pathology with Type 2B VWD, a finding that may aid in the diagnosis of 2B patients with normal VWD panel. Interestingly, the response to DDAVP in low vWF patient was detected by PCA and correlated with improvement in vWD panel. Perfusion chamber technology adapted for use in a clinical setting could provide a rapid, simple, low blood volume method to evaluate patients with abnormal bleeding. With additional patient studies this methodology may provide a useful screening tool prior to moving to more complex, expensive, detailed platelet function studies. Disclosures: Stephens: Portola Pharmaceuticals Inc: Employment.