Neutralizing antibodies against adeno-associated virus examined prospectively in pediatric patients with hemophilia

Recombinant adeno-associated virus (rAAV) is a promising gene delivery vector and has recently been used in patients with hemophilia. One limitation of AAV application is that most humans have experienced wild-type AAV serotype 2 exposure, which frequently generates neutralizing antibodies (NAbs) that may inhibit rAAV2 vector transduction. Employing alternative serotypes of rAAV vectors may circumvent this problem. We investigated the development of NAbs in early childhood by examining sera gathered prospectively from 62 children with hemophilia A, participating in a multi-institutional hemophilia clinical trial (the Joint Outcome Study). Clinical applications in hemophilia therapy have been suggested for serotypes AAV2, AAV5 and AAV8, therefore NAbs against these serotypes were serially assayed over a median follow-up of 4 years. NAbs prevalence increased during early childhood for all serotypes. NAbs against AAV2 (43.5%) were observed more frequently and at higher titers compared with both AAV5 (25.8%) and AAV8 (22.6%). NAbs against AAV5 or AAV8 were rarely observed in the absence of co-prevalent and higher titer AAV2 NAbs, suggesting that NAbs to AAV5 and AAV8 were detected following AAV2 exposure due to partial cross-reactivity of AAV2-directed NAbs. The results may guide rational design of clinical trials using alternative AAV serotypes and suggest that younger patients who are given AAV gene therapy will benefit from the lower prevalence of NAbs.

Validation of a new pediatric joint scoring system from the International Hemophilia Prophylaxis Study Group: validity of the hemophilia joint health score

OBJECTIVE

Repeated hemarthrosis in hemophilia causes arthropathy with pain and dysfunction. The Hemophilia Joint Health Score (HJHS) was developed to be more sensitive for detecting arthropathy than the World Federation of Hemophilia (WFH) physical examination scale, especially for children and those using factor prophylaxis. The HJHS has been shown to be highly reliable. We compared its validity and sensitivity to the WFH scale.

METHODS

We studied 226 boys with mild, moderate, and severe hemophilia at 5 centers. The HJHS was scored by trained physiotherapists. Study physicians at each site blindly determined individual and total joint scores using a series of visual analog scales.

RESULTS

The mean age was 10.8 years. Sixty-eight percent were severe (93% of whom were treated with prophylaxis), 15% were moderate (24% treated with prophylaxis), and 17% were mild (3% treated with prophylaxis). The HJHS correlated moderately with the physician total joint score (rs=0.42, P<0.0001) and with overall arthropathy impact (rs=0.42, P<0.0001). The HJHS was 97% more efficient than the WFH at differentiating severe from mild and moderate hemophilia. The HJHS was 74% more efficient than the WFH at differentiating subjects treated with prophylaxis from those treated on demand. We identified items on the HJHS that may be redundant or rarely endorsed and could be removed from future versions.

CONCLUSION

Both the HJHS and WFH showed evidence of strong construct validity. The HJHS is somewhat more sensitive for mild arthropathy; its use should be considered for studies of children receiving prophylaxis.

Simultaneous thrombin and plasmin generation capacities in normal and abnormal states of coagulation and fibrinolysis in children and adults

INTRODUCTION

Thrombin and plasmin are the key enzymes involved in coagulation and fibrinolysis, respectively. Plasma coagulative and fibrinolytic potentials in normal children and adults, and in representative pathologically altered hemostatic states, were evaluated via simultaneous assessment of thrombin and plasmin generation.

MATERIALS AND METHODS

An assay of Simultaneous Thrombin and Plasmin generation (STP) was developed to measure thrombin and plasmin in plasma using individual fluorometric substrates. Coagulation is initiated with dilute tissue factor, phospholipid, and calcium in platelet-poor plasma; fibrinolysis is accelerated via tissue plasminogen activator (tPA). Abnormal states of hemostasis were investigated.

RESULTS

STP assay reproducibility and normal adult and pediatric values for measured and calculated parameters have been established. Onset of both thrombin and plasmin generation was significantly delayed in children relative to adults (p<0.001) and the maximum amplitudes of thrombin and plasmin generation were less in children than adults (p<0.01). No significant differences were measured among pediatric age groups. The most profound impairments in thrombin generation were observed for extrinsic and common pathway factor deficiencies, with the exception of afibrinogenemia. Plasmin generation was severely impaired in deficiencies of fibrinogen and plasminogen as well as with decreased tPA reagent concentration and addition of aminocaproic acid. Plasmin generation was greatly enhanced by alpha-2-antiplasmin deficiency and excess tPA reagent.

CONCLUSION

Simultaneous assessment of thrombin and plasmin generation in plasma shows promise for affording an enhanced understanding of overall coagulative and fibrinolytic functions in physiological and pathologically altered states of hemostasis in children and adults.

Percutaneous mechanical and pharmacomechanical thrombolysis for occlusive deep vein thrombosis of the proximal limb in adolescent subjects: findings from an institution-based prospective inception cohort study of pediatric venous thromboembolism

PURPOSE

Young individuals with occlusive, proximal-limb deep vein thrombosis (DVT) who have acutely increased plasma levels of factor VIII and D-dimer are at high risk for postthrombotic syndrome (PTS) when treated with conventional anticoagulation alone. The present report is an evaluation of experience with adjunctive percutaneous mechanical thrombolysis (PMT) and/or percutaneous pharmacomechanical thrombolysis (PPMT) in such patients.

PATIENTS AND METHODS

Among 95 children 11-21 years of age enrolled in a prospective cohort of venous thromboembolism between March 1, 2006, and November 1, 2009, 16 met eligibility criteria and underwent PMT/PPMT, typically with adjunctive catheter-directed thrombolytic infusion (CDTI) of tissue-type plasminogen activator given after the procedure.

RESULTS

Median age was 16 years (range, 11-19 y). Thirteen cases (81%) involved lower limbs. Underlying stenotic lesions were disclosed in 53%, with endovascular stents deployed in all cases of May-Thurner anomaly. There were no periprocedural major bleeding events and one symptomatic pulmonary embolism. Technical success rate was 94%. Early (< 30 days) locally recurrent DVT developed in 40% of cases, of which 83% were successfully treated with repeat lysis. Late recurrent DVT rate (median follow-up duration, 14 months; range, 1-42 mo) was 27%. Cumulative incidence of physically and functionally significant PTS at 1-2 years was 13%.

CONCLUSIONS

This experience provides preliminary evidence that PMT/PPMT with adjunctive CDTI can be used safely and effectively in adolescent subjects with DVT at high risk for PTS.

The roles of anatomic factors, thrombophilia, and antithrombotic therapies in childhood-onset arterial ischemic stroke

Childhood-onset arterial ischemic stroke (AIS) is a rare disorder with high risks of both recurrent stroke and life-long neurological morbidity. Anatomic risk factors for primary and/or recurrent AIS include a venous thrombotic source for paradoxical embolism via a patent foramen ovale, primary cardioembolism, extracranial dissection, and intracranial arteriopathies, among others. Genetic and acquired thrombophilias are common, some of which have been shown to have prognostic influence on risk of recurrent AIS. While knowledge of childhood AIS risk factors has grown considerably in recent years, an evidence-based understanding of optimal antithrombotic therapy strategies has not yet been attained. Consensus-based guidelines have been developed, but future research must emphasize identification of additional prognostic factors and the initiation of cooperative randomized controlled clinical trials.

Meeting unmet needs in inhibitor patients

For patients with haemophilia, the development of inhibitors complicates treatment, and inhibitor patients may thus have a range of unmet needs. Although successful inhibitor eradication will render patients responsive to factor replacement therapy, with potentially beneficial effects on long-term outcomes, this may not always be possible. Physicians treating inhibitor patients should aim to achieve reliable control of bleeding episodes, and the prevention of joint disease should also be a priority. Patients with high-titre inhibitors require therapy with bypassing agents--recombinant activated factor VII (rFVIIa) or a plasma-derived activated prothrombin complex concentrate (pd-APCC)--for the treatment of bleeding. When treating joint haemorrhage in inhibitor patients, both aggressive treatment of intercurrent joint bleeds and prophylaxis should be considered, although evidence is needed as to whether prophylaxis with bypassing agents can significantly delay/prevent the development of osteochondral changes in patients with inhibitors. Despite physicians' best efforts, joint disease may ultimately occur in inhibitor patients, and in such instances optimizing treatment, of both early and late stages, is important. There is no single therapeutic modality for dealing with the various treatment challenges posed by inhibitor patients, but overall goals should be to improve quality of life, with the provision of cost-effective care that aims to maintain physical function.

Comparison of characteristics from White- and Black-Americans with venous thromboembolism: a cross-sectional study

When compared with Whites, Black-Americans may have a 40% higher incidence venous thromboembolism (VTE) incidence. However, whether other VTE characteristics and risk factors vary by race is uncertain. To compare demographic and baseline characteristics among White- and Black-Americans with VTE, we used data prospectively collected from consecutive consenting adults enrolled in seven Centers for Disease Control (CDC) Thrombosis and Hemostasis Centers from August 2003 to March 2009. These characteristics were compared among Whites (n = 2002) and Blacks (n = 395) with objectively diagnosed VTE, both overall, and by age and gender. When compared with Whites, Blacks had a significantly higher proportion with pulmonary embolism (PE), including idiopathic PE among Black women, and a significantly higher proportion of Blacks were women. Blacks had a significantly higher mean BMI and a significantly lower proportion with recent surgery, trauma or infection, family history of VTE, and documented thrombophilia (solely from reduced factor V Leiden and prothrombin G20210A prevalence). Conversely, Blacks had a significantly higher proportion with hypertension, diabetes mellitus, chronic renal disease and dialysis, HIV, and sickle cell disease. When compared with White women, Black women had a significantly lower proportion with recent oral contraceptive use or hormone therapy. We conclude that Whites and Blacks differ significantly regarding demographic and baseline characteristics that may be risk factors for VTE. The prevalence of transient VTE risk factors and idiopathic VTE among Blacks appears to be lower and higher, respectively, suggesting that heritability may be important in the etiology of VTE among Black-Americans.

Post-thrombotic syndrome in children: a systematic review of frequency of occurrence, validity of outcome measures, and prognostic factors

BACKGROUND

Post-thrombotic syndrome is a manifestation of chronic venous insufficiency following deep venous thrombosis. This systematic review was conducted to critically evaluate pediatric evidence on frequency of occurrence, validity of outcome measures, and prognostic indicators of post-thrombotic syndrome.

DESIGN AND METHODS

A comprehensive literature search of original reports revealed 19 eligible studies, totaling 977 patients with upper/lower extremity deep venous thrombosis. Calculated weighted mean frequency of post-thrombotic syndrome was 26% (95% confidence interval: 23-28%) overall, and differed significantly by prospective/non-prospective analysis and use/non-use of a standardized outcome measure.

RESULTS

Standardized post-thrombotic syndrome outcome measures included an adaptation of the Villalta scale, the Clinical-Etiologic-Anatomic-Pathologic classification, and the Manco-Johnson instrument. Data on validity were reported only for the Manco-Johnson instrument. No publications on post-thrombotic syndrome-related quality of life outcomes were identified. Candidate prognostic factors for post-thrombotic syndrome in prospective studies included use/non-use of thrombolysis and plasma levels of factor VIII activity and D-dimer.

CONCLUSIONS

Given that affected children must endure chronic sequelae for many decades, it is imperative that future collaborative pediatric prospective cohort studies and trials assess as key objectives and outcomes the incidence, severity, prognostic indicators, and health impact of post-thrombotic syndrome, using validated measures.

Biomarkers of hypercoagulability and inflammation in childhood-onset arterial ischemic stroke

OBJECTIVE

To test the hypothesis that acute elevations of biomarkers of hypercoagulability and inflammation are common in children with arterial ischemic stroke (AIS), particularly among etiologic subtypes that carry an increased risk of recurrent stroke.

STUDY DESIGN

In this prospective/retrospective institutional-based cohort study of acute childhood-onset AIS (n = 50) conducted between 2005 and 2009, D-dimer, factor VIII (FVIII) activity, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) were serially evaluated at the time of clinical blood sampling. Patients were classified by stroke subtype as cardioembolic, moyamoya, non-moyamoya arteriopathy, or other.

RESULTS

Both D-dimer and CRP were frequently elevated in acute childhood-onset AIS and exhibited a decreasing trend with time. Acute D-dimer levels were significantly higher in cardioembolic AIS compared with noncardioembolic AIS (median, 2.04 microg/mL [range 0.54-4.54 microg/mL] vs 0.32 microg/mL [0.22-3.18 microg/mL]; P = .002). At an optimal threshold of > or = 0.50 microg/mL, the sensitivity and specificity of D-dimer for cardioembolic subtype were 78% and 79%, respectively.

CONCLUSIONS

Our findings identify D-dimer and CRP as candidate biomarkers for etiology and prognosis in childhood-onset AIS. Further studies should investigate the role of these and other biomarkers of hypercoagulability and inflammation in childhood-onset AIS.

Pharmacokinetics and safety of fibrinogen concentrate

BACKGROUND

Although fibrinogen concentrate has been available for the treatment of congenital fibrinogen deficiency for years, knowledge of its pharmacokinetics comes from only two small studies.

OBJECTIVES

To assess the pharmacokinetic (PK) profile, clot integrity and safety of fibrinogen concentrate (human) (FCH) in patients with afibrinogenemia.

PATIENTS AND METHODS

A multinational, prospective, open-label, uncontrolled study of patients with afibrinogenemia > or = 6 years of age was conducted in the USA and Italy. Plasma was collected before and after infusion for PK analyses and evaluation by rotational thromboelastometry of maximum clot firmness (MCF) to assess clot integrity. Safety was assessed on the basis of adverse events and laboratory parameters.

RESULTS

After a single dose of 70 mg kg(-1) body weight (b.w.) FCH in 14 patients, median incremental in vivo recovery was a 1.7 mg dL(-1) increase per mg kg(-1) b.w., and median levels were 1.3 g L(-1) for fibrinogen activity and antigen 1 h after infusion. Median half-life (t(1/2)) was 77.1 h for fibrinogen activity and 88.0 h for antigen. Plasma recovery in children < 16 years old was similar to that in adults aged 16 to < 65 years, but the t(1/2) and area under the curve were decreased, with an increased steady-state volume and clearance. MCF increased by a mean of 8.9 mm from baseline to 1 h after infusion of FCH (P < 0.0001). All four adverse events reported were mild, and none was serious or related to study drug.

CONCLUSIONS

These PK findings confirm a rapid increase in plasma fibrinogen levels after infusion with FCH. Together with the clot integrity and safety data and published data on efficacy, the results support the idea that FCH substitution can restore hemostasis with a good safety profile.

Athletic participation in severe hemophilia: bleeding and joint outcomes in children on prophylaxis

OBJECTIVES

We sought to determine joint outcomes relative to impact level of athletic participation among school-aged children who had hemophilia and were taking prophylactic factor replacement, as well as to investigate prognostic factors for joint outcomes.

METHODS

School-aged boys with severe hemophilia A or B at a single center were included in the study. Clinical data on baseline joint status, BMI, hemophilia treatment, bleeding episodes, joint assessments, athletic participation, and injuries were retrospectively reviewed. Data on athletic participation were supplemented, when incomplete in the medical record, via structured telephone interview.

RESULTS

Among 37 children with severe hemophilia A or B receiving factor prophylaxis, 73% participated in high-impact activities, whereas 27% participated in exclusively low-impact activities. The frequency of joint hemorrhages and new injuries did not appreciably differ between high- and low-impact athletics. In most instances, children developed <1 bleed or injury per season. A new target joint developed in 1 (3%) child. Sixteen percent of children met established BMI criteria for overweight, and 3% were obese. In logistic regression analyses with adjustment for prophylaxis frequency, level of athletic participation was not a significant prognostic factor for joint hemorrhage.

CONCLUSIONS

In the setting of regular prophylaxis and adult coaching and supervision, significant bleeding complications were uncommon and level of impact of athletic participation was not a prognostic factor for joint outcomes. Athletic participation with appropriate supervision and precautions should be encouraged in children with hemophilia receiving prophylaxis, given potential health benefits in an increasingly overweight pediatric population.

Protein C deficiency

Severe protein C deficiency (i.e. protein C activity <1 IU dL(-1)) is a rare autosomal recessive disorder that usually presents in the neonatal period with purpura fulminans (PF) and severe disseminated intravascular coagulation (DIC), often with concomitant venous thromboembolism (VTE). Recurrent thrombotic episodes (PF, DIC, or VTE) are common. Homozygotes and compound heterozygotes often possess a similar phenotype of severe protein C deficiency. Mild (i.e. simple heterozygous) protein C deficiency, by contrast, is often asymptomatic but may involve recurrent VTE episodes, most often triggered by clinical risk factors. The coagulopathy in protein C deficiency is caused by impaired inactivation of factors Va and VIIIa by activated protein C after the propagation phase of coagulation activation. Mutational analysis of symptomatic patients shows a wide range of genetic mutations. Management of acute thrombotic events in severe protein C deficiency typically requires replacement with protein C concentrate while maintaining therapeutic anticoagulation; protein C replacement is also used for prevention of these complications around surgery. Long-term management in severe protein C deficiency involves anticoagulation with or without a protein C replacement regimen. Although many patients with severe protein C deficiency are born with evidence of in utero thrombosis and experience multiple further events, intensive treatment and monitoring can enable these individuals to thrive. Further research is needed to better delineate optimal preventive and therapeutic strategies.

Clinical and laboratory diagnosis of von Willebrand disease: a synopsis of the 2008 NHLBI/NIH guidelines

Von Willebrand factor (VWF) mediates blood platelet adhesion and accumulation at sites of blood vessel injury, and also carries coagulation factor VIII (FVIII) that is important for generating procoagulant activity. Von Willebrand disease (VWD), the most common inherited bleeding disorder, affects males and females, and reflects deficiency or defects of VWF that may also cause decreased FVIII. It may also occur less commonly as an acquired disorder (acquired von Willebrand syndrome). This article briefly summarizes selected features of the March 2008 evidence-based clinical and laboratory diagnostic recommendations from the National Heart, Lung, and Blood Institute (NHLBI) Expert Panel for assessment for VWD or other bleeding disorders or risks. Management of VWD is also addressed in the NHLBI guidelines, but is not summarized here. The VWD guidelines are available at the NHLBI Web site (http://www.nhlbi.nih.gov/guidelines/vwd).

Anticoagulation in childhood-onset arterial ischemic stroke with non-moyamoya arteriopathy: findings from the Colorado and German (COAG) collaboration

BACKGROUND AND PURPOSE

Childhood arterial ischemic stroke treatment guidelines recommend extended anticoagulation in cardioembolism and dissection. We sought to investigate the safety of extended anticoagulation in childhood arterial ischemic stroke with nonmoyamoya arteriopathy, for which the risk of recurrent stroke is high.

METHODS

Thirty-seven patients with childhood-onset arterial ischemic stroke with acute arteriopathy (excluding moyamoya) were diagnosed between 1999 and 2007 and treated with anticoagulation for at least 4 weeks. Patients were followed in hospital-based cohort studies at 2 centers and systematically assessed for bleeding episodes and recurrent events.

RESULTS

Over a cumulative anticoagulation duration of 1329 patient-months, there were no major bleeding episodes and 2 clinically relevant bleeding episodes. Cumulative probability of recurrent arterial ischemic stroke at 1 year was 14%.

CONCLUSIONS

Anticoagulation can be used safely for secondary arterial ischemic stroke prevention in children with acute nonmoyamoya arteriopathy. Anticoagulation is worthy of evaluation in future randomized, controlled treatment trials in this disease.

The evaluation and management of neonatal coagulation disorders

Neonatal hemostatic abnormalities can present diagnostic and therapeutic challenges to the physician. Developmental deficiencies and/or increases of certain coagulation proteins, coupled with acquired or genetic risk factors, can result in a hemorrhagic or thromboembolic emergency. The timely diagnosis of a congenital hemorrhagic or thrombotic disorder can avoid significant long-term sequelae. However, due to the lack of randomized clinical trials addressing the management of neonatal coagulation disorders, treatment strategies are usually empiric and not evidence-based. In this chapter, we will review the neonatal hemostatic system and will discuss the most common types of hemorrhagic and thrombotic disorders. Congenital and acquired risk factors for hemorrhagic and thromboembolic disorders will be presented, as well as current treatment options. Finally, suggested evaluations for neonates with either hemorrhagic or thromboembolic problems will be reviewed.

Pharmacokinetics of protein C and antithrombin in the fetal lamb: a model to predict human neonatal replacement dosing

BACKGROUND

The preterm infant is at risk for consumptive coagulopathy and thrombosis due to late maturation of coagulation regulatory proteins. Replacement proteins are available, but neonatal pharmacokinetic data are lacking.

OBJECTIVE

The objective was to determine the pharmacokinetic properties of antithrombin (AT) and protein C (PC) in order to provide data for estimating doses in human infants.

METHODS

A catheterized ovine model was used to determine pharmacokinetic properties of AT and PC, including plasma recovery, volume of distribution (V(d)), clearance (Cl) and half-life (t((1/2))), in the fetal lamb relative to the ewe.

RESULTS

AT studies showed statistically significant differences between ewes and fetuses in recovery (p < 0.0001), V(d) (p = 0.0002) and Cl (p < 0.0001). The AT t((1/2)) was significantly shortened among fetuses (5.55 h, 95% CI: 4.01-7.08) compared to ewes (18.7 h, 95% CI: 11.6-25.8). PC recovery (p < 0.0001), V(d) (p < 0.0001) and Cl (p = 0.004) differed significantly between ewes and singleton fetuses as did the t((1/2)): 3.86 h (95% CI: 3.35-4.36) and 11.9 h (95% CI: 10.9-12.9) in the singletons and ewes, respectively. All PC parameters were significantly different for twins compared to ewes.

CONCLUSIONS

AT and PC show decreased recovery and t((1/2)) in the fetal lamb. These data can be used to estimate dosing for human neonates in comparison with human adult dosing recommendations.

Influence of factor IX on overall plasma coagulability and fibrinolytic potential as measured by global assay: monitoring in haemophilia B

We sought to determine the influence of factor IX (FIX) deficiency upon overall coagulative and fibrinolytic capacities in plasma using the clot formation and lysis (CloFAL) assay, and to investigate the role of this global assay as an adjunctive monitoring tool in haemophilia B. CloFAL assay parameters were measured in vitro in platelet-poor plasma in relation to FIX activity and antigen (FIX:Ag), and were determined ex vivo among FIX-deficient patients (n = 41) in comparison to healthy individuals (n = 48). Supplementation of FIX-deficient plasma with FIX in vitro demonstrated a non-linear concentration dependence of FIX upon overall plasma coagulability. Ex vivo, coagulability was significantly decreased in FIX-deficient vs. healthy subjects among adults [median coagulation index (CI): 4% vs. 104% respectively; P < 0.001] and children (median CI: 9% vs. 63%; P < 0.001). Fibrinolytic capacity was increased in adult FIX-deficient vs. healthy subjects (median fibrinolytic index: 216% vs. 125%, respectively, P < 0.001), and was supported by a trend in shortened euglobulin lysis time (ELT). Severe haemophilia B patients showed heterogeneity in aberrant CloFAL assay waveforms, influenced partly by FIX:Ag levels. Patients with relatively preserved FIX:Ag (i.e. dysfunctional FIX) exhibited a shorter time to maximal amplitude in clot formation than those with type I deficiency. During patient treatment monitoring, markedly hypocoagulable CloFAL assay waveforms normalized following 100% correction with infused FIX. The CloFAL global assay detects FIX deficiency, demonstrates differences in coagulability between dysfunctional FIX and type I deficiency, and appears useful as an adjunctive test to routine FIX measurement in monitoring haemophilia B treatment.

Prophylaxis versus episodic treatment to prevent joint disease in boys with severe hemophilia

BACKGROUND

Effective ways to prevent arthropathy in severe hemophilia are unknown.

METHODS

We randomly assigned young boys with severe hemophilia A to regular infusions of recombinant factor VIII (prophylaxis) or to an enhanced episodic infusion schedule of at least three doses totaling a minimum of 80 IU of factor VIII per kilogram of body weight at the time of a joint hemorrhage. The primary outcome was the incidence of bone or cartilage damage as detected in index joints (ankles, knees, and elbows) by radiography or magnetic resonance imaging (MRI).

RESULTS

Sixty-five boys younger than 30 months of age were randomly assigned to prophylaxis (32 boys) or enhanced episodic therapy (33 boys). When the boys reached 6 years of age, 93% of those in the prophylaxis group and 55% of those in the episodic-therapy group were considered to have normal index-joint structure on MRI (P=0.006). The relative risk of MRI-detected joint damage with episodic therapy as compared with prophylaxis was 6.1 (95% confidence interval, 1.5 to 24.4). The mean annual numbers of joint and total hemorrhages were higher at study exit in the episodic-therapy group than in the prophylaxis group (P<0.001 for both comparisons). High titers of inhibitors of factor VIII developed in two boys who received prophylaxis; three boys in the episodic-therapy group had a life-threatening hemorrhage. Hospitalizations and infections associated with central-catheter placement did not differ significantly between the two groups.

CONCLUSIONS

Prophylaxis with recombinant factor VIII can prevent joint damage and decrease the frequency of joint and other hemorrhages in young boys with severe hemophilia A. (ClinicalTrials.gov number, NCT00207597 [ClinicalTrials.gov].).

Central venous access device infections in children with hemophilia: a comparison of prophylaxis and episodic therapy

Prophylaxis was recommended as the optimal treatment regimen for severe hemophilia by several expert committees. This led to increased utilization of prophylaxis and, subsequently, central venous access devices (CVADs). Although prophylaxis is the preferred treatment, episodic therapy is used by many. CVADs are employed to facilitate administration of prophylactic and episodic infusions; however, there are no data on the risk of CVAD-related infections for prophylaxis compared with episodic therapy. Data from the Study for the Prevention of Joint Disease in Preschool Children with Severe Hemophilia, a randomized clinical trial of prophylaxis versus episodic therapy, were used to evaluate the association between CVAD-related infection and treatment. The crude and adjusted rate ratios for first CVAD-related infection per 1000 CVAD days associated with episodic therapy versus prophylaxis were 1.42 (95% confidence interval: 0.46-4.40) and 1.23 (95% confidence interval: 0.33-4.56), respectively. Although we cannot make a definitive statement about treatment and CVAD-related infection risk, this study suggests that prophylaxis likely does not put children at higher risk of CVAD-related infection than episodic therapy. Given the need for CVADs in some children and the benefits of prophylaxis, we conclude there is no reason to recommend against prophylaxis on the basis of existing knowledge of CVAD-related infection risk.

Influence of factor VIII on overall coagulability and fibrinolytic potential of haemophilic plasma as measured by global assay: monitoring in haemophilia A

The objectives of the present study were to evaluate the analytical sensitivity of the recently developed Clot Formation and Lysis (CloFAL) global assay for factor VIII (FVIII) deficiency, both in vitro and ex vivo, to determine whether this global assay is influenced by FVIII inhibitors, and to investigate the coagulative response to FVIII replacement in haemophilia A patients using the CloFAL assay in comparison with FVIII activity. Among adults and children alike, the CloFAL assay coagulation index (CI) was significantly decreased in FVIII-deficient vs. healthy subjects (adults median CI: 2% vs. 94% respectively; children median CI: 3% vs. 63%; P < 0.001 for each), and correlated significantly with activated partial thromboplastin time-based FVIII activity across all individuals (r = 0.78; P < 0.001). The CloFAL assay was analytically sensitive to deficient FVIII activity and also influenced by the presence of von Willebrand factor. Severe haemophilia A patients without inhibitory antibodies to FVIII showed considerable heterogeneity in CloFAL assay waveforms, despite a uniformly diminished CI of 0-1%. During FVIII infusion half-life studies in patients with severe haemophilia A, the CloFAL assay demonstrated a marked rise in coagulability 30 min following infusion, with progressive decrease in coagulability towards baseline over the ensuing 48-h period. In each case, the profile of coagulative response to FVIII infusion as determined by CloFAL assay CI differed qualitatively from that measured by FVIII activity. These findings indicate that the CloFAL assay may be useful as an adjunctive test to FVIII activity measurements in the therapeutic monitoring of haemophilia A.

Preanalytical conditions that affect coagulation testing, including hormonal status and therapy

Preanalytical conditions, be they due to the individual's physiologic state or to exogenous factors, can affect coagulation factors, in either a transient or a persistent manner, and need to be considered in laboratory testing. These conditions include physical and mental stress, diurnal variation, hormone levels and posture at the time of blood drawing. While testing of these factors has not been exhaustive and some results are conflicting, guidelines for testing conditions can be given.

A thrombolytic regimen for high-risk deep venous thrombosis may substantially reduce the risk of postthrombotic syndrome in children

Important predictors of adverse outcomes of thrombosis in children, including postthrombotic syndrome (PTS), have recently been identified. Given this knowledge and the encouraging preliminary pediatric experience with systemic thrombolysis, we sought to retrospectively analyze our institutional experience with a thrombolytic regimen versus standard anticoagulation for acute, occlusive deep venous thrombosis (DVT) of the proximal lower extremities in children in whom plasma factor VIII activity and/or D-dimer concentration were elevated at diagnosis, from within a longitudinal pediatric cohort. Nine children who underwent the thrombolytic regimen and 13 who received standard anticoagulation alone were followed from time of diagnosis with serial clinical evaluation and standardized PTS outcome assessments conducted in uniform fashion. The thrombolytic regimen was associated with a markedly decreased odds of PTS at 18 to 24 months compared with standard anticoagulation alone, which persisted after adjustment for significant covariates of age and lag time to therapy (odds ratio [OR] = 0.018, 95% confidence interval [CI] = < 0.001-0.483; P = .02). Major bleeding developed in 1 child, clinically judged as not directly related to thrombolysis for DVT. These findings suggest that the use of a thrombolysis regimen may safely and substantially reduce the risk of PTS in children with occlusive lower-extremity acute DVT, providing the basis for a future clinical trial.