Lack of anti-factor Xa assay standardization results in significant low molecular weight heparin (enoxaparin) dose variation in neonates and children

The relationship between INTEM/HEPTEM coagulation time ratio and heparin plasma concentration in obstetric patients: an exploratory in vitro investigation

PURPOSE

Unfractionated heparin continues to be one of the main agents used for thromboprophylaxis in obstetrics, which can complicate the placement of neuraxial anesthetics. In this study, we explored the relationship between a point-of-care coagulation test (thromboelastometry) and plasma heparin concentrations in vitro.

METHODS

We obtained blood from consenting obstetric patients with uncomplicated pregnancies in their third trimester who were not in labour and had a specific hematocrit range. Blood was processed and analyzed. We added increasing amounts of unfractionated heparin to samples from 0 to 0.3 U·mL^-1 in 0.05 U·mL^-1 increments to simulate increasing doses of unfractionated heparin. We performed INTEM and HEPTEM testing in parallel with activated partial thromboplastin time (aPTT) testing. We created a model of the relationship between heparin concentration and the INTEM/HEPTEM coagulation time (IH CT) ratio using nonlinear regression. A similar model for aPTT was also created.

RESULTS

Seventy-seven patients were included in the study. Only one concentration of heparin was added to blood samples of each patient. At a concentration of 0.05 U·mL^-1, the IH CT ratio was less than or equal to 1.1 in 9/11 (82%) samples. Activated partial thromboplastin time was not prolonged (> 35 sec) until a concentration of 0.1 U·mL^-1 heparin was added. In all samples, the IH CT ratio was prolonged at a concentration ≥ 0.2 U·mL^-1 as measured by thromboelastometry; however, at no concentration of heparin was aPTT prolonged in all samples.

CONCLUSION

The point-of-care IH CT ratio may be useful in identifying the presence of little to no heparin activity. Further research is needed to determine if this ratio can predict heparin activity in vivo.

How to use low-molecular-weight heparin to treat neonatal thrombosis in clinical practice

Among children, neonates have the highest incidence of thrombosis due to risk factors such as catheter instrumentation, an evolving coagulation system and congenital heart disease. Low-molecular-weight heparins (LMWHs) are the most commonly used anticoagulants in neonates. Published guidelines delineate dosing and monitoring protocols for LMWH therapy in newborns. However, challenging clinical situations frequently present that warrant healthcare providers to think critically beyond the range of guidelines, and judiciously resolve specific problems. This review describes the use of LMWH in the neonatal population, including practical aspects such as route and site of administration, preparation from concentrated formulations and methods to minimize pain of subcutaneous injection. It is followed by a discussion on dosing, monitoring and outcomes of LMWH therapy in neonates. The risk of recurrence of thrombosis in neonates after LMWH therapy is approximately 3% based on a pooled analysis of studies reporting this outcome over the last 24 years. The article concludes with an overview of the side-effects of LMWH, including the risk of bleeding which is around 4% based on pooled analyses of more than 30 studies.

Quality performance for indirect Xa inhibitor monitoring in patients using international external quality data

Objectives Chromogenic anti-activated factor X (FXa) assays are currently the "gold standard" for monitoring indirect anticoagulants. However, anti-FXa has been shown to vary according to the choice of reagents. In the present study, the performance of anti-FXa measurement was evaluated in order to gain more insight into the clinical applications. Furthermore, the longitudinal coefficient of variation (CV) was studied to investigate whether there is improvement over time. Methods Laboratory tests results were evaluated for samples spiked with unfractionated heparin (UFH), low-molecular-weight-heparin (LMWH), fondaparinux and danaparoid sodium. External quality assessment (EQA) data from multiple years were used from more than 100 laboratories. Results Comparison of the results for all methods showed significant differences in measured values between the frequently used methods (ANOVA: p < 0.001). The largest differences were observed for LMWH and UFH measurements. These differences may be caused by differences in method composition, such as the addition of dextran sulphate. Substantial interlaboratory variation in anti-FXa monitoring was observed for all parameters, particularly at low concentrations. Our results showed that below 0.35 IU/mL, the CVs for UFH and LMWH increase dramatically and results below this limit should be used with caution. Conclusions Our study demonstrates that the choice of the anti-FXa method is particularly important for UFH and LMWH measurement. The variation in measurements may have an effect on clinical implications, such as therapeutic ranges. Furthermore, the longitudinal EQA data demonstrated a constant performance and, in at least 50% of the cases, improvement in the CV% of the anti-Xa results over time.

Diagnosis and Management of Pediatric Venous Thromboembolism: New Therapies on the Horizon

ABSTRACT

The incidence of venous thromboembolism (VTE) is increasing in pediatric patients. Prompt recognition and evaluation of VTE in young patients could prevent significant morbidity or mortality. In contrast to VTE in adults, current treatment guidelines are largely based on expert opinion as limited randomized controlled trial data exist about the appropriate management in pediatric patients with traditional anticoagulants. However, recently approved direct-acting oral anticoagulants in adults are also being investigated in pediatric VTE and these data could inform future evidence-based treatment principles. Thus, healthcare providers must be well informed about the management of pediatric VTE and the data from these trials to date. This continuing medical education article will provide a summary of management of pediatric VTE with particular emphasis on emerging direct-acting oral anticoagulants.

Diagnosis and management of cerebral venous sinus thrombosis in children: a single-center retrospective analysis

PURPOSE

Cerebral venous thrombosis (CVT) is a rare disease in children, characterized by partial or total occlusion of blood flow in the cerebral venous system. The aim of this study is to describe clinical presentation, neuroimaging features, therapeutic management, and outcome of children with CVT.

METHODS

We retrospectively analyzed the data, including clinical manifestations, laboratory data, neurological findings, and treatment of children with radiologically confirmed CVT, admitted between January 2010 and March 2020 to our hospital. Cases of CVT complicating brain surgery were excluded.

RESULTS

We enrolled 24 children with CVT. Infection was the main etiology (58.3%), followed by trauma in 16.7% of cases. In the remaining 25% of cases, the cause was identified only in one patient presenting a thrombophilic factor. The most frequent site of thrombosis was the superficial venous system (86.8%), with multiple localizations disclosed in 79% of patients. All children received anticoagulant therapy with low molecular weight heparin (LMWH). One patient died for systemic complications of an underlying disease. No patient developed hemorrhagic events during the therapy, lasting from 35 to 360 days (mean 86 days). In all but one surviving patients (22 out of 24), recanalization of the sinus was observed at AngioMRI performed during follow-up. No neurological complications of CVT were recorded (mean follow-up: 1.5 year).

CONCLUSIONS

CVT may present with subtle and unspecific clinical manifestations in children. High level of suspicion should be kept in trauma and sinusitis. Anticoagulation treatment is safe and effective and should be promptly started to improve outcome.

Impact of exogenous antithrombin on low molecular weight heparin anti-Xa activity assays in a pediatric and young adult leukemia and lymphoma cohort with variable antithrombin levels

BACKGROUND

Low molecular weight heparin (LMWH) remains the most commonly prescribed pediatric anticoagulant. There is debate whether LMWH anti-Xa assays with or without exogenous antithrombin (AT) best reflect anticoagulation effect, and how much discrepancy exists between assay types.

OBJECTIVES

We assessed the effect of variable AT activity on LMWH anti-Xa levels in plasma samples from anticoagulated pediatric and young adult acute lymphoblastic leukemia and lymphoma (ALL/L) patients, using two instruments and their commercial kits with and without exogenous AT (ie, four platforms).

METHODS

We analyzed LMWH anti-Xa levels on 60 plasma samples with known AT activity from 12 enoxaparin-treated ALL/L patients, using four commercial kits from Siemens and Stago containing AT or not, on Siemens BCS and Stago STA R Max, respectively.

RESULTS

Of 236/240 samples with interpretable results, mean AT activity was 80% (46-138%). Correlation was acceptable for published kit ranges of LMWH anti-Xa levels when comparing kits containing AT (r = 0.82, P < .0001), or not (r = 0.93, P < .0001), and within a manufacturer (Berichrom to Innovance, r = 0.92, P < .0001; Stachrom to STA-Liquid Anti-Xa r = 0.98, P < .0001). LMWH anti-Xa levels were lower in platforms without added AT (P < .0001). For Stago kits, this effect increased when AT < 70% (P = .001, n = 19, mean 56%). Assay variability, measured as mean percent difference, was less pronounced with Stago kits (14.7%, n = 49) than Siemens (41.9%, n = 50).

CONCLUSIONS

Although LMWH levels from anti-Xa assays with added AT trend higher than in those without, correlation was fairly good between platforms in pediatric ALL/L plasmas, even when AT activity was <70%.

Predicting Anticoagulation Need for Otogenic Intracranial Sinus Thrombosis: A Machine Learning Approach

Objective  The role of anticoagulation (AC) in the management of otogenic cerebral venous sinus thrombosis (OCVST) remains controversial. Our study aims to better define when AC is used in OCVST. Methods  MEDLINE, EMBASE, and The Cochrane Library were searched from inception to February 14, 2019 for English and English-translated articles. References cited in publications meeting search criteria were searched. Titles and abstracts were screened and identified in the literature search, assessing baseline risk of bias on extracted data with the methodological index for nonrandomized studies (MINORS) scale. Random effects meta-regression followed by random forest machine learning analysis across 16 moderator variables between AC and nonanticoagulated (NAC) cohorts was conducted. Results  A total of 92% of treated patients were free of neurologic symptoms at the last follow-up (mean 29.64 months). Four percent of AC and 14% of NAC patients remained symptomatic (mean 18.72 and 47.10 months). 3.5% of AC patients experienced postoperative wound hematomas. AC and NAC recanalization rates were 81% (34/42) and 63% (five-eights), respectively. OCVST was correlated with cholesteatoma and intracranial abscess. Among the analyzed covariates, intracranial abscess was most predictive of AC and cholesteatoma was most predictive of NAC. Comorbid intracranial abscess and cholesteatoma were predictive of AC. Conclusion  The present study is the first to utilize machine learning algorithms in approaching OCVST. Our findings support the therapeutic use of AC in the management of OCVST when complicated by thrombophilia, intracranial abscess, and cholesteatoma. Patients with intracranial abscess and cholesteatoma may benefit from AC and surgery. Patients with cholesteatoma can be managed with NAC and surgery.

Intravenous Enoxaparin in Pediatric Burn Patients: A Case Series

Patients with acute burns experience a hypercoagulable state that may necessitate the use of anticoagulants to prevent the complications of venous thromboembolism (VTE). Enoxaparin is a low molecular weight heparin that is commonly used for this purpose; however, the traditional SC route of administration poses potential limitations in the pediatric burn population. These include pain upon injection, increased anxiety, erroneous absorption and distribution, and difficulty in finding an administration site when burns encompass a large percentage of body surface area. As a result, the IV route of administration may be preferable in these patients. To date, a limited number of studies in critically ill pediatric patients have been performed. In this report, we present a case series of 3 pediatric burn patients who initially received SC enoxaparin and were transitioned to IV enoxaparin for VTE prophylaxis. The patients were 2, 8, and 10 years old. Burn involvement ranged from 8% to 75% total body surface area, and all patients had central line access. Adequate prophylactic low molecular weight heparin anti-Xa peak concentrations (0.1-0.3 international units/mL) were achieved with IV doses ranging from 0.35 to 0.5 mg/kg administered every 12 hours. No adverse effects, major bleeding events, or treatment failures occurred.

Clinical features and treatment results in preterm infants with intracardiac thrombus

INTRODUCTION

Thrombus incidence is higher among neonates, especially in preterm infants, due to the associated additional risk factors.

MATERIALS AND METHODS

The medical recordings of premature infants who had been diagnosed as having intracardiac thrombus between January 2016 and January 2019 were evaluated retrospectively. We use recombinant tissue plasminogen activator when the thrombus is relatively large compared to left atrium, pedunculated, mobile, or snake shaped.

RESULTS

A total of 13 premature patients were diagnosed as having intracardiac thrombus during the 3-year period. All were diagnosed during echocardiographic studies. Low molecular weight heparin was administered in four patients. In three, recombinant tissue plasminogen activator was started with low dose (0.01 mg/kg/h) and increased gradually to 0.06 mg/kg/h. In three, recombinant tissue plasminogen activators were started with standard dose (0.5 mg/kg/h). In one recombinant tissue, plasminogen activator was started with low dose (0.01 mg/kg/h) and increased to standard dose. Two patients died before treatment, three patients died during treatment, follow-up was not available for two patients, and thrombus completely resolved in six patients.

DISCUSSION

In preterm babies with risk factors, intracardiac thrombus should be kept in mind during all echocardiographic studies. In our patients, low and standard dose regimens were used, and the treatment results were similar.

Pulmonary Embolism in Children

Pulmonary embolism is an uncommon but potentially life-threatening event in children. There has been increasing awareness of pulmonary embolism in children with improved survival in children with systemic disease and advancements in diagnostic modalities. However, literature regarding pulmonary embolism in children is sparse, and thus current guidelines for management of pulmonary embolism in children are extrapolated from adult literature and remain controversial. This article reviews the background and pathophysiology of venous thromboembolism, as well as current diagnostic approach and recommended management of pulmonary embolism in children.

Management of thrombosis in children and neonates: practical use of anticoagulants in children

Venous thrombosis (VTE) in children and neonates presents numerous management challenges. Although increasing in frequency, VTE in children and neonates is still uncommon compared with adults. The epidemiology of VTE is vastly different in neonates vs children vs adolescents vs adults. In reality, pediatric thrombosis should be viewed as a multitude of rare diseases (eg, renal vein thrombosis, spontaneous thrombosis, catheter-related thrombosis, cerebral sinovenous thrombosis), all requiring different approaches to diagnosis and with different short- and long-term consequences, but linked by the use of common therapeutic agents. Further, children have fundamentally different physiology in terms of blood flow, developmental hemostasis, and, likely, endothelial function. The American Society of Hematology 2017 Guidelines for Management of Venous Thromboembolism: Treatment of Pediatric VTE provides up-to-date evidence-based guidelines related to treatment. Therefore, this article will focus on the practical use of therapeutic agents in the management of pediatric VTE, especially unfractionated heparin, low-molecular-weight heparin, and oral vitamin K antagonists, as the most common anticoagulants used in children. Direct oral anticoagulants (DOACs) remain in clinical trials in children and should not be used outside of formal trials for the foreseeable future.

Anticoagulant prophylaxis and therapy in children: current challenges and emerging issues

This review is aimed at describing the unique challenges of anticoagulant prophylaxis and treatment in children, and highlighting areas for research for improving clinical outcomes of children with thromboembolic disease. The evidence presented demonstrates the challenges of advancing the evidence base informing optimal management of thromboembolic disease in children. Recent observational studies have identified risk factors for venous thromboembolism in children, but there are few interventional studies assessing the benefit-risk balance of using thromboprophylaxis in risk-stratified clinical subgroups. A risk level-based framework is proposed for administering mechanical and pharmacological thromboprophylaxis. More research is required to refine the assignment of risk levels. The anticoagulants currently used predominantly in children are unfractionated heparin, low molecular weight heparin, and vitamin K antagonists. There is a paucity of robust evidence on the age-specific pharmacology of these agents, and their efficacy and safety for prevention and treatment of thrombosis in children. The available literature is heterogeneous, reflecting age-specific differences, and the various clinical settings for anticoagulation in children. Monitoring assays and target ranges are not well established. Nevertheless, weight-based dosing appears to achieve acceptable outcomes in most indications. Given the limitations of the classical anticoagulants for children, there is great interest in the direct oral anticoagulants (DOACs), whose properties appear to be particularly suitable for children. All DOACs currently approved for adults have Pediatric Investigation Plans ongoing or planned. These are generating age-specific formulations and systematic dosing information. The ongoing pediatric studies still have to establish whether DOACs have a positive benefit-risk balance in the various pediatric indications and age groups.

Association of outcomes and anti-Xa levels in the treatment of pediatric venous thromboembolism

BACKGROUND

There are few data in the pediatric population evaluating the relationship between measured anti-Xa levels during enoxaparin therapy and thrombotic outcomes.

OBJECTIVE

To determine whether there is a difference in outcomes in children who receive enoxaparin with mean anti-Xa levels between 0.45 and 0.79 unit/ml (low therapeutic range) versus between 0.80 and 1.05 unit/ml (high therapeutic range) throughout their course of their treatment.

METHODS

We retrospectively identified subjects with uncomplicated venous thromboembolism treated with enoxaparin.

RESULTS

Of 69 patients with any response to therapy, 48 (70%) had mean anti-Xa levels in the low therapeutic range and 21 (30%) had mean anti-Xa levels in the high therapeutic range. Of 20 patients with no documented response to therapy, 13 (65%) had mean anti-Xa levels in the low therapeutic range and 7 (35%) had mean anti-Xa levels in the high therapeutic range. Forty-eight (79%) of the 61 patients with low-range mean anti-Xa level had any response to therapy. Twenty-one (75%) of the 28 patients with high-range mean anti-Xa level had any response to therapy. Chi-square test (P = 0.080) and logistic regression (OR = 1.23, P = 0.70) demonstrated no significant association between mean anti-Xa range (lower vs. upper) and therapy response.

CONCLUSIONS

There was no statistically significant difference between low-range versus high-range mean anti-Xa levels and thrombus resolution. Empiric clinical practices of targeting anti-Xa levels in the higher therapeutic range to achieve better outcomes may not be warranted.

Clinical Feasibility of Monitoring Enoxaparin Anti-Xa Concentrations: Are We Getting It Right?

Background: Anti-Xa monitoring is utilized to measure the extent of anticoagulation in certain patient populations receiving enoxaparin. It is essential to accurately obtain this pharmacodynamic marker for safe and effective anticoagulation management. Objectives: To determine the frequency of correctly drawn anti-Xa concentrations in accordance with predefined institutional criteria and to determine the number of dose adjustments implemented based on incorrectly drawn anti-Xa concentrations. Methods: This was a retrospective, single-center, cohort study among adult patients who received treatment doses of enoxaparin with measured anti-Xa concentrations. Patients were excluded if they were pregnant, on hemodialysis, or received prophylactic dosing. Anti-Xa levels were defined as correctly measured if they were drawn 3 to 5 hours after the dose during steady state concentrations. Descriptive statistics were performed and analyzed via SPSS software. Results: Overall, 203 patients were reviewed and 59 patients with 74 anti-Xa levels were included. The majority of anti-Xa levels (57/74; 77%) were drawn incorrectly and often resulted in collection of repeat anti-Xa samples. There were 12 documented dose adjustments and approximately 42% (5/12) were based on incorrectly drawn anti-Xa levels. Anti-Xa levels were within target range approximately 45% of the time. Conclusions: Enoxaparin anti-Xa concentrations are frequently drawn incorrectly and dose adjustments are often performed based on these unsupported anti-Xa levels. This may present a potential risk to compromise patient safety.