The impact of extended half-life factor concentrates on prophylaxis for severe hemophilia in the United States.

With licensure of extended half-life (EHL) factor products and the changing landscape of available hemophilia products, patients and providers have options for less treatment-intense prophylaxis. The impact of these products in clinical practice to date remains understudied. We aimed to quantify the use of EHL products in prophylaxis in the US using the ATHN-dataset, a database of 145 ATHN-affiliated hemophilia treatment centers (HTCs). Further, we aimed to quantify the impact of EHL on key hemophilia indicators including annualized bleed rates (ABRs), hemophilia joint health scores (HJHS) and quality of life (QOL) metrics. The use of EHL vs standard half-life (SHL) products in severe hemophilia was compared between June 2018 and March 2019 using the ATHN-dataset. A cohort of patients was also recruited from seven participating HTCs in order to compare ABR, HJHS and QOL between product classes. By March 2019 the number of individuals with severe Hemophilia A (SHA) receiving EHLs remained relatively stable (28.4%), whereas the number of prescribed non-factor products increased to 7.1%, with a diminishing majority of patients (64.0%) continuing to receive SHLs. The majority of patients with severe hemophilia B (SHB) received treatment with EHLs including 57.5% by March 2019. There was a trend toward lower ABR with use of EHLs in SHA and SHB, although this did not result in improved HJHS nor QOL. EHL use in the United States in severe hemophilia continues to increase, although at a slower rate in SHA with the availability of non-factor therapy. The impact of the EHL therapies in clinical practice should continue to be examined prospectively.

Laboratory misdiagnosis of von Willebrand disease in post-menarchal females: A multi-center study.

Increased awareness of von Willebrand Disease (VWD) has led to more frequent diagnostic laboratory testing, which insurers often dictate be performed at a facility with off-site laboratory processing, instead of a coagulation facility with onsite processing. Off-site processing is more prone to preanalytical variables causing falsely low levels of von Willebrand Factor (VWF) due to the additional transport required. Our aim was to determine the percentage of discordance between off-site and onsite specimen processing for VWD in this multicenter, retrospective study. We enrolled females aged 12 to 50 years who had off-site specimen processing for VWF assays, and repeat testing performed at a consulting institution with onsite coagulation phlebotomy and processing. A total of 263 females from 17 institutions were included in the analysis. There were 251 subjects with both off-site and onsite VWF antigen (VWF:Ag) processing with 96 (38%) being low off-site and 56 (22%) low onsite; 223 subjects had VWF ristocetin co-factor (VWF:RCo), 122 (55%) were low off-site and 71 (32%) were low onsite. Similarly, 229 subjects had a Factor VIII (FVIII) assay, and 67 (29%) were low off-site with less than half, 29 (13%) confirmed low with onsite processing. Higher proportions of patients demonstrated low VWF:Ag, VWF:RCo, and/or FVIII with off-site processing compared to onsite (McNemar's test P-value <.0005, for all assays). These results emphasize the need to decrease delays from sample procurement to processing for VWF assays. The VWF assays should ideally be collected and processed at the same site under the guidance of a hematologist.

Assessment of neonatal, cord, and adult platelet granule trafficking and secretion.

Despite the transient hyporeactivity of neonatal platelets, full-term neonates do not display a bleeding tendency, suggesting potential compensatory mechanisms which allow for balanced and efficient neonatal hemostasis. This study aimed to utilize small-volume, whole blood platelet functional assays to assess the neonatal platelet response downstream of the hemostatic platelet agonists thrombin and adenosine diphosphate (ADP). Thrombin activates platelets via the protease-activated receptors (PARs) 1 and 4, whereas ADP signals via the receptors P2Y1 and P2Y12 as a positive feedback mediator of platelet activation. We observed that neonatal and cord blood-derived platelets exhibited diminished PAR1-mediated granule secretion and integrin activation relative to adult platelets, correlating to reduced PAR1 expression by neonatal platelets. PAR4-mediated granule secretion was blunted in neonatal platelets, correlating to lower PAR4 expression as compared to adult platelets, while PAR4 mediated GPIIb/IIIa activation was similar between neonatal and adult platelets. Under high shear stress, cord blood-derived platelets yielded similar thrombin generation rates but reduced phosphatidylserine expression as compared to adult platelets. Interestingly, we observed enhanced P2Y1/P2Y12-mediated dense granule trafficking in neonatal platelets relative to adults, although P2Y1/P2Y12 expression in neonatal, cord, and adult platelets were similar, suggesting that neonatal platelets may employ an ADP-mediated positive feedback loop as a potential compensatory mechanism for neonatal platelet hyporeactivity.

Pediatric trauma venous thromboembolism prediction algorithm outperforms current anticoagulation prophylaxis guidelines: a pilot study.

PURPOSE: Venous thromboembolism (VTE) in injured children is rare, but sequelae can be morbid and life-threatening. Recent trauma society guidelines suggesting that all children over 15 years old should receive thromboprophylaxis may result in overtreatment. We sought to evaluate the efficacy of a previously published VTE prediction algorithm and compare it to current recommendations. METHODS: Two institutional trauma registries were queried for all pediatric (age < 18 years) patients admitted from 2007 to 2018. Clinical data were applied to the algorithm and the area under the receiver operating characteristic (AUROC) curve was calculated to test algorithm efficacy. RESULTS: A retrospective review identified 8271 patients with 30 episodes of VTE (0.36%). The VTE prediction algorithm classified 51 (0.6%) as high risk (> 5% risk), 322 (3.9%) as moderate risk (1-5% risk) and 7898 (95.5%) as low risk (< 1% risk). AUROC was 0.93 (95% CI 0.89-0.97). In our population, prophylaxis of the 'moderate-' and 'high-risk' cohorts would outperform the sensitivity (60% vs. 53%) and specificity (96% vs. 77%) of current guidelines while anticoagulating substantially fewer patients (373 vs. 1935, p < 0.001). CONCLUSION: A VTE prediction algorithm using clinical variables can identify injured children at risk for venous thromboembolic disease with more discrimination than current guidelines. Prospective studies are needed to investigate the validity of this model. LEVEL OF EVIDENCE: III-Clinical decision rule evaluated in a single population.

Platelet Disorders.

After vascular injury and exposure of subendothelial matrix proteins to the intravascular space, mediators of hemostasis are triggered and allow for clot formation and restoration of vascular integrity. Platelets are the mediators of primary hemostasis, creating a platelet plug and allowing for initial cessation of bleeding. Platelet disorders, qualitative and quantitative, may result in bleeding signs and symptoms, particularly mucocutaneous bleeding such as epistaxis, bruising, petechiae, and heavy menstrual bleeding. Increasing evidence suggests that platelets have functional capabilities beyond hemostasis, but this review focuses solely on platelet hemostatic properties. Herein, normal platelet function as well as the effects of abnormal function and thrombocytopenia are reviewed.

Second-line treatments in children with immune thrombocytopenia: Effect on platelet count and patient-centered outcomes.

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder with isolated thrombocytopenia and hemorrhagic risk. While many children with ITP can be safely observed, treatments are often needed for various reasons, including to decrease bleeding, or to improve health related quality of life (HRQoL). There are a number of available second-line treatments, including rituximab, thrombopoietin-receptor agonists, oral immunosuppressive agents, and splenectomy, but data comparing treatment outcomes are lacking. ICON1 is a prospective, multi-center, observational study of 120 children starting second-line treatments for ITP designed to compare treatment outcomes including platelet count, bleeding, and HRQoL utilizing the Kids ITP Tool (KIT). While all treatments resulted in increased platelet counts, romiplostim had the most pronounced effect at 6 months (P = .04). Only patients on romiplostim and rituximab had a significant reduction in both skin-related (84% to 48%, P = .01 and 81% to 43%, P = .004) and non-skin-related bleeding symptoms (58% to 14%, P = .0001 and 54% to 17%, P = .0006) after 1 month of treatment. HRQoL significantly improved on all treatments. However, only patients treated with eltrombopag had a median improvement in KIT scores at 1 month that met the minimal important difference (MID). Bleeding, platelet count, and HRQoL improved in each treatment group, but the extent and timing of the effect varied among treatments. These results are hypothesis generating and help to improve our understanding of the effect of each treatment on specific patient outcomes. Combined with future randomized trials, these findings will help clinicians select the optimal second-line treatment for an individual child with ITP.

Pilot study of novel lab methodology and testing of platelet function in adolescent women with heavy menstrual bleeding.

BackgroundApproximately 40% of adolescent women experience heavy menstrual bleeding (HMB), and 10-62% of them have an underlying bleeding disorder (BD). Diagnosing a BD remains challenging because of limitations of available clinical platelet function assays. The aim of this study was to characterize platelet function in a population of adolescent women with HMB using small-volume whole-blood assays.MethodsAnticoagulated whole blood was used to assess platelet GPIIbIIIa activation, α-granule secretion, and aggregation in response to multiple agonists. Platelet adhesion on collagen or von Willebrand Factor (VWF) under static and shear flow was also assessed.ResultsFifteen participants with HMB were included in the study, of which eight were diagnosed with a clinically identifiable BD. Platelet activation was blunted in response to calcium ionophore in participants without a BD diagnosis compared with that in all other participants. Impaired GPIIbIIIa activation was observed in response to all GPCR agonists, except adenosine diphosphate (ADP), in participants with qualitative platelet disorders. Our assays detected platelet aggregation in the majority of participants with a BD in response to ADP, collagen-related peptide (CRP), thrombin receptor activator 6 (TRAP-6), or U46619. Platelet adhesion and aggregation on collagen and VWF was decreased for participants with VWD.ConclusionParticipants with and without BD exhibited aberrant platelet function in several assays in response to select agonists.

Physician decision making in selection of second-line treatments in immune thrombocytopenia in children.

Immune thrombocytopenia (ITP) is an acquired autoimmune bleeding disorder which presents with isolated thrombocytopenia and risk of hemorrhage. While most children with ITP promptly recover with or without drug therapy, ITP is persistent or chronic in others. When needed, how to select second-line therapies is not clear. ICON1, conducted within the Pediatric ITP Consortium of North America (ICON), is a prospective, observational, longitudinal cohort study of 120 children from 21 centers starting second-line treatments for ITP which examined treatment decisions. Treating physicians reported reasons for selecting therapies, ranking the top three. In a propensity weighted model, the most important factors were patient/parental preference (53%) and treatment-related factors: side effect profile (58%), long-term toxicity (54%), ease of administration (46%), possibility of remission (45%), and perceived efficacy (30%). Physician, health system, and clinical factors rarely influenced decision-making. Patient/parent preferences were selected as reasons more often in chronic ITP (85.7%) than in newly diagnosed (0%) or persistent ITP (14.3%, P = .003). Splenectomy and rituximab were chosen for the possibility of inducing long-term remission (P < .001). Oral agents, such as eltrombopag and immunosuppressants, were chosen for ease of administration and expected adherence (P < .001). Physicians chose rituximab in patients with lower expected adherence (P = .017). Treatment choice showed some physician and treatment center bias. This study illustrates the complexity and many factors involved in decision-making in selecting second-line ITP treatments, given the absence of comparative trials. It highlights shared decision-making and the need for well-conducted, comparative effectiveness studies to allow for informed discussion between patients and clinicians.

Neonatal platelets: mediators of primary hemostasis in the developing hemostatic system.

The human hemostatic system is developmentally regulated, resulting in qualitative and quantitative differences in the mediators of primary and secondary hemostasis as well as fibrinolysis in neonates and infants. Although gestational age-related differences in coagulation factor levels occur, the existence of a unique neonatal platelet phenotype remains controversial. Complicated by difficulties in obtaining adequate neonatal blood volumes with which to perform functional assays, ambiguity surrounds the characterization of neonatal platelets. Thus, much of the current knowledge of neonatal platelet function has been based on studies from cord blood samples. Studies suggest that cord blood-derived platelets, as a surrogate for neonatal platelets, are hypofunctional when compared with adult platelets. This relative platelet dysfunction, combined with a propensity toward thrombocytopenia in the neonatal intensive care unit population, creates a clinical conundrum regarding the appropriate administration of platelet transfusions. This review provides an appraisal of the distinct functional phenotype of neonatal platelets. Neonatal platelet transfusion practices and the impact of the relatively hypofunctional neonatal platelet on those practices will be considered.

p21 activated kinase signaling coordinates glycoprotein receptor VI-mediated platelet aggregation, lamellipodia formation, and aggregate stability under shear.

OBJECTIVE: Rho GTPase proteins play a central role in regulating the dynamics of the platelet actin cytoskeleton. Yet, little is known regarding how Rho GTPase activation coordinates platelet activation and function. In this study, we aimed to characterize the role of the Rho GTPase effector, p21 activated kinase (PAK), in platelet activation, lamellipodia formation, and aggregate formation under shear. APPROACH AND RESULTS: Stimulation of platelets with the glycoprotein receptor VI agonist, collagen-related peptide, rapidly activated PAK in a time course preceding phosphorylation of PAK substrates, LIM domain kinase LIMK1 and the MAPK/ERK kinase MEK, and the subsequent activation of MAPKs and Akt. Pharmacological inhibitors of PAK blocked signaling events downstream of PAK and prevented platelet secretion as well as platelet aggregation in response to collagen-related peptide. PAK inhibitors also prevented PAK activation and platelet spreading on collagen surfaces. PAK was also required for the formation of platelet aggregates and to maintain aggregate stability under physiological shear flow conditions. CONCLUSIONS: These results suggest that PAK serves as an orchestrator of platelet functional responses after activation downstream of the platelet collagen receptor, glycoprotein receptor VI.

The PAK system links Rho GTPase signaling to thrombin-mediated platelet activation.

Regulation of the platelet actin cytoskeleton by the Rho family of small GTPases is essential for the proper maintenance of hemostasis. However, little is known about how intracellular platelet activation from Rho GTPase family members, including Rac, Cdc42, and Rho, translate into changes in platelet actin structures. To better understand how Rho family GTPases coordinate platelet activation, we identified platelet proteins associated with Rac1, a Rho GTPase family member, and actin regulatory protein essential for platelet hemostatic function. Mass spectrometry analysis revealed that upon platelet activation with thrombin, Rac1 associates with a set of effectors of the p21-activated kinases (PAKs), including GIT1, ßPIX, and guanine nucleotide exchange factor GEFH1. Platelet activation by thrombin triggered the PAK-dependent phosphorylation of GIT1, GEFH1, and other PAK effectors, including LIMK1 and Merlin. PAK was also required for the thrombin-mediated activation of the MEK/ERK pathway, Akt, calcium signaling, and phosphatidylserine (PS) exposure. Inhibition of PAK signaling prevented thrombin-induced platelet aggregation and blocked platelet focal adhesion and lamellipodia formation in response to thrombin. Together, these results demonstrate that the PAK signaling system is a key orchestrator of platelet actin dynamics, linking Rho GTPase activation downstream of thrombin stimulation to PAK effector function, MAP kinase activation, calcium signaling, and PS exposure in platelets.

Venous thromboembolic screening in pediatric trauma: A prospective cohort study of risk-stratified ultrasonography.

BACKGROUND: This prospective observational cohort study evaluates risk-stratified venous thromboembolism (VTE) screening in injured children. While the reported incidence of VTE is 6% to 10% among critically injured children, there is no standard for screening. Venous thromboembolism may have long-term sequelae in children, including postthrombotic syndrome. METHODS: Patients admitted to a level 1 pediatric trauma center were risk stratified for VTE using a validated prediction algorithm. Children at high risk (risk scores ≥523; i.e., ≥1% risk) received screening duplex ultrasonography. Children at moderate risk (risk scores 410-522; i.e., 0.3-0.99% risk) were screened as a comparison/control. RESULTS: Three-hundred fifty-five children were consecutively risk stratified from October 2019 to May 2021. Forty-seven children received screening duplex ultrasounds: 21 from a high-risk cohort and 26 from a moderate-risk cohort. Four children were diagnosed with VTE in the high-risk cohort compared with seven in the moderate-risk cohort ( p = 0.53). Total incidence of VTE among screened children was 23.4% (11 of 47). Asymptomatic VTE accounted for 81.8% of all events (9 of 11). Fifty-four percent (6 of 11) of VTE were central venous catheter associated. Venous thromboembolism in surviving children resolved by 3 to 6 months with no symptoms of postthrombotic syndrome after 1 year. No cases of VTE were identified in unscreened children, yielding an institutional VTE incidence of 3.1% (11 of 355). DISCUSSION: Risk-stratified screening demonstrates a significant incidence of asymptomatic VTE in injured children. These results may guide reevaluation of prediction algorithms developed from symptomatic VTE risk and longitudinal study of the sequelae of asymptomatic VTE. LEVEL OF EVIDENCE: Prognostic and Epidemiological; Level III.

Building the foundation for a community-generated national research blueprint for inherited bleeding disorders: research to advance the health of people with inherited bleeding disorders with the potential to menstruate.

BACKGROUND: People who have or had the potential to menstruate (PPM) with inherited bleeding disorders (BD) face particular challenges receiving appropriate diagnosis and care and participating in research. As part of an initiative to create a National Research Blueprint for future decades of research, the National Hemophilia Foundation (NHF) and American Thrombosis and Hemostasis Network conducted extensive all-stakeholder consultations to identify the priorities of PPM with inherited BDs and those who care for them. RESEARCH DESIGN AND METHODS: Working group (WG) 4 of the NHF State of the Science Research Summit distilled community-identified priorities for PPM with inherited BDs into concrete research questions and scored their feasibility, impact, and risk. RESULTS: WG4 identified important gaps in the foundational knowledge upon which to base optimal diagnosis and care for PPM with inherited BDs. They defined 44 top-priority research questions concerning lifespan sex biology, pregnancy and the post-partum context, uterine physiology and bleeding, bone and joint health, health care delivery, and patient-reported outcomes and quality-of-life. CONCLUSIONS: The needs of PPM will best be advanced with research designed across the spectrum of sex and gender biology, with methodologies and outcome measures tailored to this population, involving them throughout.

Up to 1% of cisgender women and girls have an inherited bleeding disorder (BD). Common symptoms include heavy menstrual bleeding (HMB), heavy bleeding after giving birth known as post-partum hemorrhage (PPH), nose bleeds, bleeding from the mouth, and excessive bleeding after surgery or procedures. They can also experience bleeding into their muscles, joints, and even into the brain. Uterine bleeding, such as from HMB and PPH, can impact the lives of anyone who has or had a uterus, a group we designate as people who have or had the potential to menstruate (PPM).Many PPM with an inherited BD do not receive diagnosis, treatment, and care needed due to a lack of expertise among health care professionals and the public, misunderstanding, and bias. Uncertainty about "normal" versus "abnormal" bleeding can contribute to a lack of diagnosis, treatment, and care. Language, such as the label of "carrier," can be a barrier to accessing treatment and care for PPM.People with inherited BDs, health care professionals with various expertise and focus, and researchers worked together to identify the research that would most improve the lives of PPM, in six focus areas where there are major gaps in knowledge and the lack of standards required for accurate diagnosis.

A Retrospective Comparison of Time to Cessation of Acute Heavy Menstrual Bleeding in Adolescents Following Two Dose Regimens of Combined Oral Hormonal Therapy.

STUDY OBJECTIVE: Although multiple hormonal treatment strategies are effective in decreasing heavy menstrual bleeding (HMB) in adolescents, few studies have compared the relative effectiveness of hormone therapy on the basis of dose. DESIGN: Retrospective chart review SETTING: Urban tertiary care institution PARTICIPANTS: Adolescents aged 9-19 years with acute HMB and anemia in 2008-2018 INTERVENTIONS: We used billing codes to identify encounters for acute HMB with hemoglobin less than 12 mg/dl and reviewed initial treatment and time until resolution of acute HMB. We excluded patients who had previously used gonadal steroids or did not complete follow-up. We then compared patients who received combined oral ethinyl estradiol with progestin (EE/P) in standard dosing (EE ≤35 mcg/day) vs taper dosing (EE >35mcg/day in any step-down regimen). MAIN OUTCOME MEASURES: Time until patient-reported resolution of acute HMB, measured in days from initial treatment RESULTS: Of 207 patients with vaginal bleeding and anemia, 90 met the criteria for review of therapy type and dose. Users of combined EE/P were hormone-naïve in 28/33 (84.8%) of those who initiated standard EE/P and 22/32 (68.8%) who initiated taper dosing. Bleeding duration was available for 15/28 (53.6%) and 18/22 (81.8%). Resolution of HMB occurred in 0-9 days with standard dosing (mean ±SD 2.1 ± 2.3 days) versus 1-15 days for taper dosing (4.9 ± 4.7; p = 0.04). Excluding six outliers of zero or more than 10 days, HMB ceased by 2.6 and 3 days (n = 12 and 15; p = 0.62). CONCLUSION: Currently recommended higher dose combined hormonal regimens do not appear to shorten the time to resolution of acute HMB in adolescents.

Provider Attitudes and Practices Regarding Intrauterine System (IUS) Insertion in Adolescents With and Without Bleeding Disorders for Management of Heavy Menstrual Bleeding.

STUDY OBJECTIVE: Heavy menstrual bleeding (HMB) may be the sentinel event for identifying a patient with a bleeding disorder (BD). The levonorgestrel intrauterine system (LNG IUS) has been proposed as a treatment for HMB in adolescents with and without BDs; however, no standard protocols for LNG IUS insertion in these populations exist. Providers were surveyed regarding the use of the LNG IUS in adolescents with HMB, with and without BD. DESIGN, SETTING, PARTICIPANTS, INTERVENTIONS, AND MAIN OUTCOME MEASURES: An institutional review board-approved survey assessing provider attitudes, LNG IUS insertion practices, and patient outcomes in adolescents with HMB, with and without BD, was electronically distributed to 3523 providers in the fields of hematology, adolescent medicine, and obstetrics and gynecology. Descriptive analysis was performed. RESULTS: A total of 312 respondents across all 3 specialties completed the survey. Nearly 100% of respondents considered the LNG IUS safe and effective treatment for adolescents with HMB, both with and without BD. Additionally, 66% of providers chose LNG IUS as the ideal treatment for HMB in patients with BD. Differences were noted in clinical setting for LNG IUS insertion, peri-procedural medication use, and post-procedure follow-up among specialties. Providers across all specialties reported low complication rates related to IUS insertion and use in both patient groups. CONCLUSION: Providers considered the LNG IUS safe and effective treatment for HMB in adolescents with and without a diagnosed BD. Practice patterns regarding LNG IUS insertion in this population vary. Further research is necessary to explore IUS outcomes in adolescent patients with HMB, with and without BD, and to inform evidence-based protocols for LNG IUS insertion.

A Cross-Sectional Study of Women and Girls with Congenital Bleeding Disorders: The American Thrombosis and Hemostasis Network Cohort.

Introduction: The number of women and girls (WG) with bleeding disorders cared for at hemophilia treatment centers has increased dramatically over the last 30 years, owing to improved recognition of bleeding symptoms specific to WG. However, basic epidemiologic data of this population remain elusive. The ATHNdataset (American Thrombosis and Hemostasis Network) is a surveillance tool for people with bleeding disorders in the United States, providing demographic as well as bleeding symptom and treatment information. The aim of this study was to characterize the female cohort within the ATHNdataset. Methods: In this retrospective cohort study, the ATHNdataset was queried for demographic data, bleeding disorder diagnosis, bleeding symptoms, and treatment. Descriptive statistics were used. Results: As of December 31, 2017, 8,820 WG with a congenital bleeding disorder were enrolled in the ATHNdataset, comprising 24.5% of the entire ATHNdataset cohort (35,945). The most common reported diagnosis was von Willebrand disease (VWD), accounting for 62.9% of the population. Reproductive tract bleeding was reported in 15.8% of participants older than 15 years. Conclusions: The ATHNdataset describes the largest cohort of WG with bleeding disorders to date. VWD is the most common diagnosis in WG with bleeding disorders. Symptoms specific to WG, such as heavy menstrual bleeding, are underreported in this data set compared with other data sources. Ongoing efforts are needed to improve diagnosis, treatment, and surveillance of WG with bleeding disorders.

Pharmacokinetic-tailored approach to hemophilia prophylaxis: Medical decision making and outcomes.

BACKGROUND: Clinical application of population pharmacokinetics (popPK) is of increasing interest to patients with hemophilia, providers, and payers. Routine use of popPK profiles in factor replacement prophylaxis decision making has the potential to maintain or improve efficacy and reduce product consumption. AIM: To investigate the feasibility of implementation and longitudinal assessment of pharmacokinetic (PK)-tailored prophylaxis in routine clinical practice for hemophilia A and to describe factors that influence decision making for prescribed hemophilia prophylaxis. METHODS: This longitudinal, multicenter, prospective feasibility study of children and adults with hemophilia A without inhibitors used the Web Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo) to generate PK profiles. Assessments over 12 weeks captured data on prescribed prophylaxis, popPK tool use, provider decision making, and patient-reported outcomes. RESULTS: Eighteen participants aged 6 to 39 years enrolled; half used extended half-life concentrates. Patient interest in their PK centered on general curiosity followed by a desire for participation in physical activity and decrease in infusion frequency. Providers used the WAPPS clinical calculator feature to simulate prophylaxis regimens under different dose, infusion, and trough conditions. Most targeted troughs were 1 to 3 IU/dL. The feasibility assessment demonstrated challenges with patient recruitment; however, the majority of participants successfully completed study assessments meeting feasibility targets. CONCLUSION: A larger-scale study powered to evaluate the impact of PK-tailored prophylaxis on clinical and patient-reported outcomes is feasible with study design modifications to support increased recruitment rate. Shared decision making incorporating patient and provider goals is important and facilitated by regimen simulations with the clinical calculator.

Neonatal Venous Thromboembolism.

Neonates are the pediatric population at highest risk for development of venous thromboembolism (VTE), and the incidence of VTE in the neonatal population is increasing. This is especially true in the critically ill population. Several large studies indicate that the incidence of neonatal VTE is up almost threefold in the last two decades. Central lines, fluid fluctuations, sepsis, liver dysfunction, and inflammation contribute to the risk profile for VTE development in ill neonates. In addition, the neonatal hemostatic system is different from that of older children and adults. Platelet function, pro- and anticoagulant proteins concentrations, and fibrinolytic pathway protein concentrations are developmentally regulated and generate a hemostatic homeostasis that is unique to the neonatal time period. The clinical picture of a critically ill neonate combined with the physiologically distinct neonatal hemostatic system easily fulfills the criteria for Virchow's triad with venous stasis, hypercoagulability, and endothelial injury and puts the neonatal patient at risk for VTE development. The presentation of a VTE in a neonate is similar to that of older children or adults and is dependent upon location of the VTE. Ultrasound is the most common diagnostic tool employed in identifying neonatal VTE, but relatively small vessels of the neonate as well as frequent low pulse pressure can make ultrasound less reliable. The diagnosis of a thrombophilic disorder in the neonatal population is unlikely to change management or outcome, and the role of thrombophilia testing in this population requires further study. Treatment of neonatal VTE is aimed at reducing VTE-associated morbidity and mortality. Recommendations for treating, though, cannot be extrapolated from guidelines for older children or adults. Neonates are at risk for bleeding complications, particularly younger neonates with more fragile intracranial vessels. Developmental alterations in the coagulation proteins as well as unique pharmacokinetics must also be taken into consideration when recommending VTE treatment. In this review, epidemiology of neonatal VTE, pathophysiology of neonatal VTE with particular attention to the developmental hemostatic system, diagnostic evaluations of neonatal VTE, and treatment guidelines for neonatal VTE will be reviewed.