## Key Points

• Thrombophilia testing does not affect clinical management in the acute setting after a TEE in children and should be avoided.

## Introduction

The incidence of pediatric venous thromboembolism (VTE) appears to be rising. Recently, a 70% to 109% increase in the rate of pediatric VTE has been reported.1,2  Greater physician awareness, improved diagnostic modalities, increased interventions such as central venous catheters (CVCs), and greater survival of medically complex children with chronic conditions all likely contribute to the rise in pediatric VTE.3  One aspect of VTE management in children includes testing for thrombophilia, often performed to gain insight into the cause of the VTE. The reported prevalence of thrombophilia in pediatric VTE varies greatly across studies and is largely based on variation in the patient population and the tests performed.4

In 2002, the Perinatal/Pediatric Scientific Sub-Committee of the International Society of Thrombosis and Haemostasis proposed that all pediatric patients with VTE or arterial thrombosis be tested for inherited and acquired thrombophilia in a tiered approach.5  These recommendations do not take into account appropriate timing of testing, how testing might affect clinical management, or additional transient prothrombotic risk factors such as CVCs, oral contraceptives, infection, prolonged immobility, trauma, or recent surgery. In contrast, the 2010 British Committee for Standards in Hematology recommended against indiscriminate inherited thrombophilia testing in unselected patients with a first diagnosis of VTE; in patients with a CVC-related thrombosis, upper limb venous thrombosis, pregnancy morbidities, and retinal vein occlusion; and in patients with arterial thrombosis.6  Moreover, in 2012, the American College of Chest Physicians proposed that the duration and intensity of anticoagulation therapy for pediatric venous or arterial thromboembolic events (TEEs) be independent of whether the patient has an inherited thrombophilia, albeit as a weak recommendation with poor evidence to support it. In addition, they recommended that management of VTE in the setting of antiphospholipid antibodies be similar to general VTE management in children.7

In adults, thrombophilia testing rarely affects acute management.8  However, data are lacking for the pediatric population. There is mounting evidence that thrombophilia testing is overused at many centers.2,9  The American Society of Hematology Choosing Wisely Campaign recommends against thrombophilia testing in adults in the setting of transient major thrombotic risk factors because the risk for harm and/or cost likely outweighs the anticipated benefits.10  Given the lack of consensus on thrombophilia testing in children and the fact that more children are likely to undergo testing as the incidence of VTEs continues to rise, we audited thrombophilia testing at our institution to explore whether thrombophilia testing affected clinical management during the acute setting. In addition, we sought to determine whether thrombophilia testing in the acute setting constituted a potential cause of harm in our cohort.

## Patients and methods

### Study population

Children’s Medical Center, Dallas, is a quaternary care children’s hospital with a dedicated hematology service responsible for primary or consultative care of patients with TEEs and includes an anticoagulation pharmacist. The anticoagulation pharmacist prospectively maintains data on all patients with a TEE in an electronic database. We conducted a retrospective audit of all consecutive patients diagnosed with a venous or arterial TEE during a 1-year period (1 January to 31 December 2015). The University of Texas Southwestern Medical Center Institutional Review Board approved the study and waived the requirement of informed consent.

### Inclusion and exclusion criteria

All subjects diagnosed with a venous or arterial TEE during the specified study period were included. Subjects were excluded if they were diagnosed with a stroke, had a history of a TEE before the study period, or already had an established thrombophilia diagnosis.

## Discussion

Our retrospective audit of pediatric patients with a TEE found that 51% were tested during the acute phase of the TEE. Although 50% of these patients tested positive during the acute phase, only 12% were ultimately diagnosed with a thrombophilia defect. None of these thrombophilia defects affected management during the acute phase. Patients were anticoagulated regardless of a positive or negative thrombophilia test result.

Interpretation of testing during the acute phase of the TEE is problematic because of ill-defined diagnostic cutoff levels, acute phase effects, and concurrent anticoagulation. For example, 3 patients had combined deficiencies of 2 natural anticoagulants, which would be extremely rare. In 2 patients, repeat testing was negative, and 1 patient never underwent repeat testing. The most common positive tests during the acute phase were a positive LA and decreased PS activity, both of which are subject to acute phase effects.8  Only 1 of these in each category remained positive when tested at 12 weeks or more. By delaying testing until after the resolution of the acute phase, more accurate results can easily be obtained. Results of thrombophilia testing did not affect decisions regarding the intensity or duration of anticoagulation in the acute phase of the TEE.

Inherited thrombophilia testing during the acute setting is only warranted in patients with purpura fulminans, vitamin K antagonist-induced skin necrosis, or heparin resistance without an identifiable cause6 ; however, none of the patients in our cohort met the abovementioned criteria. Although 1 patient received extended anticoagulation because of persistent elevation of high-titer aβ2GPI, one could argue the patient would have received extended anticoagulation even if tested after resolution of the acute phase. Furthermore, although the evidence is weak, American College of Chest Physicians guidelines do suggest management as per general recommendations for VTE management in the setting of antiphospholipid antibodies.7  Thrombophilia testing may have influenced thromboprophylaxis during future high-risk situations in 5 subjects (all with FVL), but was only documented for 1 in our cohort. Despite this finding, deferring thrombophilia testing may have yielded more accurate results. Some contend that every pediatric patient with a history of a TEE should receive prophylactic anticoagulation during high-risk situations independent of a thrombophilia disorder.3

Thrombophilia testing was potentially harmful in 12 patients younger than 1 year (including 1 neonate). With decreased total blood volumes, this population is most at risk for iatrogenic anemia.16  Two patients required repeat testing because of false-positive test results. Fortunately, none of the patients were misdiagnosed with a thrombophilia or received unnecessary long-term anticoagulation. This is likely because our institutional practices dictate that every patient with a TEE follow-up with a pediatric hematologist. This is unlike in the adult population, where many such patients are not followed by hematologists.8  There is also a substantial potential for misdiagnosis based on erroneous laboratory results if the patient follows up with physicians without hemostasis thrombosis expertise.

An estimated \$82 000 in annual cost resulting from unnecessary testing is not insignificant. This does not include the costs associated with repeat testing, phlebotomist time, blood loss, and physician time counseling parents. In addition, the FVL PCR test instead of the activated protein C resistance assay further increases costs.17  The activated protein C resistance assay is also more clinically useful for detecting a prothrombotic FV phenotype,17  can be modified to account for the different levels of coagulation factors in children, and can be used for patients with a history of bone marrow or liver transplant.18

Evidence-based indications for thrombophilia testing in pediatric population are lacking.3  The 2002 International Society of Thrombosis and Haemostasis guidelines suggest universal testing of all pediatric patients with a VTE.5  The primary objective of thrombophilia testing is to identify patients at high risk for recurrent thrombosis and possibly determine anticoagulation duration on the basis of the presence of positive thrombophilia markers. However, prior pediatric studies have demonstrated this may not be cost-effective.19  A meta-analysis of inherited thrombophilia markers by Young et al20  showed odds ratios for recurrent pediatric VTE ranging from 0.64 (95% CI, 0.35-1.18) for FVL to 4.46 (95% CI, 2.89-6.89) in patients with combined disorders. However, subgroup analysis for catheter-related VTEs was not performed separately. A more recent meta-analysis by Neshat-Vahid et al21  found only weak associations of FVL, factor VIII activity, and PC deficiency in pediatric patients with catheter-related VTEs. The authors recommend against routine thrombophilia testing in these patients with a catheter-related VTE because of the weak associations, low prevalence of the thrombophilia markers in the meta-analysis, and limited evidence on the use of thrombophilia tests to guide anticoagulation. In a subgroup analysis of our patients with only catheter-related TEEs, the relative risk of developing a recurrent TEE in patients who never had testing (28 patients; median follow-up, 425 days) compared with patients who had some form of testing at any point, whether during or after the acute setting (29 patients; median follow-up, 567 days), was 0.26 (95% CI, 0.03-2.2). There was no difference in the risk of developing a recurrent TEE based on thrombophilia testing. Of the 4 patients who had testing and later developed a recurrent TEE, all recurrent events were also associated with a catheter. None of these patients had a thrombophilia defect, underscoring the fact that thrombophilia testing in children with catheter-related TEEs is likely unwarranted and can be avoided.

Limitations of our study include a lack of comparison with controls. The low rate of follow-up testing of an initial positive result (63%) likely underestimated the number of children with a confirmed thrombophilia defect. However, this did not affect our primary study objective. We were also unable to determine if thrombophilia testing affected management in asymptomatic family members. Furthermore, our median follow-up time may not have been long enough to determine a statistically significant difference in the risk for recurrent TEEs in patients with catheter-related TEEs who were or were not tested.

In conclusion, our retrospective study demonstrates that thrombophilia testing during the acute setting does not impact clinical management and was not cost effective at our institution. Even in patients with a confirmed thrombophilia defect, long-term management was only rarely altered. Based on these results, we recommend against routine thrombophilia testing during the acute TEE setting except for rare conditions such as patients with purpura fulminans, vitamin K antagonist-induced skin necrosis, heparin resistance, or in the setting of a clinical trial.

## Acknowledgment

A.Z. is supported by a grant from the National Institutes of Health, National Heart Lung, and Blood Institute (1K23HL132054-01).

## Authorship

Contribution: C.G. gathered the data, analyzed the results, and drafted the manuscript; and R.S. and A.Z. critically edited the manuscript.

Conflict-of-interest disclosure: R.S. serves as a consultant for CSL Behring and Octapharma. The remaining authors declare no competing financial interests.

Correspondence: Ayesha Zia, Division of Pediatric Hematology/Oncology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390; e-mail: ayesha.zia@utsouthwestern.edu.

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