Thrombophilia states and markers of coagulation activation in the prediction of pediatric venous thromboembolic outcomes: a comparative analysis with respect to adult evidence

The Impact of Multiple Risk Factors for Venous Thromboembolism and Its Implications for Management

Venous thromboembolism (VTE) is a rare multifactorial disorder in childhood with an annual incidence of about 0.07 to 0.14 per 10 000 children. A 15-year-old female with a body mass index of 48 kg/m² who endorsed oral contraceptive use presented with clinical findings consistent with deep venous thrombosis along with the presence of a pulmonary embolism. Further workup revealed that the patient was heterozygous for factor V Leiden and homozygous for prothrombin G20210A mutations. There are no current pediatric guidelines for the antithrombotic management of patients with multiple risk factors for VTE. Two such risk factors, obesity and the use of estrogen-containing hormone contraceptives, have been implicated in adult VTE cases but have not been clearly delineated in pediatric patients. The need for guidance regarding the VTE management of these patients has become more apparent given the increasing incidence of childhood obesity and the number of adolescents using oral contraceptives. Additionally, thrombophilia testing remains controversial though testing may be indicated in asymptomatic first-degree relatives and in families with antithrombin, protein C, or protein S deficiencies. Given the increased incidence of multiple risk factors for VTE, there is also a need to develop a comprehensive risk assessment tool for pediatric patients at high risk of VTE.

Effectiveness of and risk associated with aspirin therapy in hemodialysis patients with a background of antiplatelet factor 4/heparin complex antibody detection

BACKGROUND

The optimal prevention measures against hemodialysis (HD)-associated complications, including all-cause thrombotic events and death, are unclear.

METHODS

This prospective study was designed to assess the effect of aspirin on prevention of HD-associated complications. Patients were divided into four groups according to platelet factor-4/heparin-complex (PF4/H) antibody detection and aspirin prescription: Group 1, antibody(-)/aspirin(+); Group 2, antibody(-)/aspirin(-); Group 3, antibody(+)/aspirin(+); and Group 4, antibody(+)/aspirin(-). Adverse events were compared among all four groups. Cox hazard regression was performed to analyze the effects of anti-PF4/H antibody and aspirin on thrombosis and death.

RESULTS

This study included 648 patients undergoing HD; 142 were positive for anti-PF4/H antibodies, and 229 had received aspirin before enrollment. During the 4-year follow-up period, 138 patients developed thrombosis, and 63 of these events were anti-PF4/H antibody-associated. A total of 112 patients died; 75 died of coronary heart disease (CHD). Group 4 had a significantly higher incidence of total and anti-PF4/H antibody-associated thrombosis events as well as total and CHD-associated death than did the other three groups. Aspirin had a preventive effect against all adverse events in anti-PF4/H antibody-positive patients, but not in antibody-negative patients. Group 1 patients with baseline D-dimer levels of <0.6μg/mL developed more hemorrhagic events than did patients in the other groups.

CONCLUSIONS

Aspirin prevention of thrombosis and death in patients undergoing HD might require consideration of the anti-PF4/H antibody status. In antibody-positive individuals, taking aspirin could improve the prognosis and therefore might be recommended. In antibody-negative individuals, prevention was minimal and the bleeding risk was obviously increased; thus, aspirin should be avoided or at least require careful evaluation prior to aspirin treatment.

Monitoring hypercoagulability and hypofibrinolysis following acute venous Thromboembolism in children: application of the CloFAL assay in a prospective inception cohort study

Although individual thrombophilia tests are frequently performed in children with venous thromboembolism (VTE), global assays provide the opportunity to fill the gap in knowledge regarding their net impact on overall coagulative (and in some cases fibrinolytic) function. We first evaluated analytic sensitivity of the Clot Formation and Lysis (CloFAL) global assay to hypercoagulability and alterations in fibrinolysis, and then characterized changes in plasma coagulative and fibrinolytic capacities over time in children with acute VTE. In plasma ex vivo and in vitro experiments, the CloFAL assay area-under-the-curve (AUC) was analytically sensitive to hypercoagulable states, and its modified fibrinolytic index (FI2) was sensitive to both hyper- and hypofibrinolytic conditions. Clinical data and plasma samples for assay were collected during follow-up of 50 children enrolled in a prospective inception cohort study of VTE from May 2006 to June 2010. Follow-up periods were designated as follows: acute (<1 month post-event), sub-acute (1-3 months), early chronic (3-12 months), and late chronic (>12 months). Since most children were sampled at fewer than three pre-defined follow-up periods, study population findings were grouped by timepoint. AUC was significantly increased, and FI(2) significantly decreased, in the acute period of VTE when compared to healthy controls, indicating hypercoagulability and hypofibrinolysis, respectively. One-third of patients were hypercoagulable, and 23% were hypofibrinolytic, in the late chronic phase. AUC and FI(2) were strongly correlated with functional fibrinogen levels. These findings indicate the utility of the CloFAL assay in monitoring plasma coagulative and fibrinolytic capacities in children with VTE. Studies of its potential role in outcome prediction are ongoing.

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.

Testing children for inherited thrombophilia: more questions than answers

Thrombotic events in children have become an increasingly common problem, particularly in paediatric tertiary care hospitals. The prevalence of inherited thrombophilia in children who develop thrombosis varies substantially depending on the population. Children who develop thrombosis, as well as those who have not but have a positive family history, are frequently tested for inherited thrombophilia. The clinical utility of performing such tests has been questioned, in both adults and children. This review will examine the practise of testing for inherited thrombophilia in children, focusing on the rationale for testing and highlighting areas in which more evidence is needed prior to making strong recommendations. Future studies, many of which are currently being performed or proposed, are necessary to address many of the unanswered questions.