Low Early Antifactor Xa Target Achievement Rate of Low-Molecular-Weight Heparin for Treating Venous Thromboembolism in Patients in Intensive Care

This study aimed to evaluate whether early antifactor Xa (anti-Xa) achieved the target range when venous thromboembolism (VTE) was treated with low-molecular-weight heparin (LMWH), based on body weight and renal function in patients treated in intensive care units (ICUs). Anti-Xa levels in patients treated with LMWH for VTE in ICU and medical wards between January 1, 2021, and June 30, 2022, were retrospectively assessed. The demographics, laboratory parameters, and early anti-Xa peak levels of patients were collected. All patients were followed up for 3 months to collect VTE recurrence/bleeding events. Univariate and multivariate linear regression analyses were used to identify the factors affecting anti-Xa levels. A total of 108 patients were enrolled in this study, including 70 patients in ICU and 38 patients on medical wards. The early anti-Xa level (0.36 vs 0.61 IU/mL, P < .001) and target achievement rate (21.4% vs 39.5%, P = .015) of patients in ICU were lower than those in medical wards. Multivariate linear regression showed that only antithrombin (AT) significantly affected anti-Xa levels in patients in ICU (β = 0.008, 95%CI 0.005 to 0.011, P < .001). There was no significant difference in VTE recurrence events (11.8% vs 7.5%, P = .628) and bleeding events (29.4% vs 17.0%, P = .304) between the early anti-Xa within-target group and the early anti-Xa below-target group. Low anti-Xa peak levels are common in patients in ICU. AT activity should be monitored when using LMWH in critically ill patients.

Anti-Xa Activity of Enoxaparin for Prevention of Venous Thromboembolism in Severe Nephrotic Syndrome-A Single Center Prospective Study

Severe nephrotic syndrome (NS) is associated with high risk of venous thromboembolic events (VTE), as well as presumably altered heparin pharmacokinetics and pharmacodynamics. Although prophylactic anticoagulation is recommended, the optimal dose is not established. The aim of the study was to test two co-primary hypotheses: of reduced enoxaparin effectiveness and of the need for dose-adjustment in NS. Forty two nephrotic patients with serum albumin ≤2.5 g/dL were alternately assigned to a standard fixed-dose of enoxaparin (NS-FD: 40 mg/day) or ideal body weight (IBW)-based adjusted-dose (NS-AD: 1 mg/kg/day). Twenty one matched non-proteinuric individuals (C-FD) also received fixed-dose. Co-primary outcomes were: the achievement of low- and high-VTE risk threshold of antifactor-Xa activity (anti-FXa) defined as 0.2 IU/mL and 0.3 IU/mL, respectively. Low-VTE-risk threshold was achieved less often in NS-FD than C-FD group (91 vs. 62%, p = 0.024), while the high-VTE-risk threshold more often in NS-AD than in NS-FD group (90 vs. 38%, p < 0.001). Two VTE were observed in NS during 12 months of follow-up (incidence: 5.88%/year). In both cases anti-FXa were 0.3 IU/mL implying the use of anti-FXa >0.3 IU/mL as a target for dose-adjustment logistic regression models. We determined the optimal dose/IBW cut-off value at 0.8 mg/kg and further developed bivariate model (termed the DoAT model) including dose/IBW and antithrombin activity that improved the diagnostic accuracy (AUC 0.85 ± 0.06 vs. AUC 0.75 ± 0.08). Enoxaparin efficacy is reduced in severe NS and the dose should be adjusted to ideal body weight to achieve target anti-FXa activity.

Life-Threatening Mediastinal Hematoma Formation After Removal of the Hemodialysis Catheter in a Boxer: A Case Report

A 4-year-old female Boxer was referred for renal replacement therapy 2 days after observed grape ingestion. An 11-French dual-lumen dialysis catheter was placed into the right jugular vein and continuous renal replacement therapy was initiated for 66 h. Afterwards the patient received enoxaparin subcutaneously as a thromboprophylaxis. Four hours after removal of the dialysis catheter the patient developed severe dyspnea with hypercapnia and signs of hemorrhagic shock. Bedside ultrasound and X-rays of the thorax revealed a soft tissue opacity dorsally of the trachea, located in the mediastinum. The findings were consistent with mediastinal bleeding and hematoma formation. Blood gas examination indicated hypoventilation. The dog was managed conservatively with multiple blood transfusions and mechanical ventilation. The patient survived to discharge, and the hematoma was fully absorbed in the radiographs after 17 days. Patients with impaired kidney function should receive individualized enoxaparin dosage adjusted to anti-Xa levels and should be strictly monitored for complications. Mediastinal hemorrhage and hematoma formation should be considered as a potential complication in patients receiving a jugular vein catheter.

C-reactive protein-induced activated partial thromboplastin time prolongation in heparinized samples is attenuated by elevated factor VIII

INTRODUCTION

Activated partial thromboplastin time (aPTT) and antifactor Xa (anti-Xa) activity are used to monitor unfractionated heparin therapy in children on extracorporeal membrane oxygenation (ECMO). Elevated C-reactive protein (CRP) can prolong aPTT and cause discrepancy between these two assays. We aimed to evaluate CRP effect on aPTT and anti-Xa assays in the presence of heparin and to determine whether elevated CRP affects laboratory monitoring in pediatric ECMO patients.

MATERIALS AND METHODS

Citrated normal specimens were spiked with CRP, heparin, and recombinant factor VIII (FVIII) and followed by measurement of aPTT and anti-Xa activity. Additionally, aPTT, anti-Xa activity, FVIII, fibrinogen, and CRP were measured in 18 ECMO specimens.

RESULTS

Elevated CRP prolonged aPTT in normal specimens with or without heparin, but did not affect anti-Xa assay. In contrast, ECMO specimens showed similar aPTT and anti-Xa values regardless of CRP level. Elevated CRP in specimens was accompanied by increased fibrinogen and FVIII activity. Additional in vitro experiments confirmed that FVIII spiked simultaneously with CRP attenuated CRP-induced aPTT prolongation in heparinized specimens.

CONCLUSION

In vitro CRP-induced aPTT prolongation is not observed in pediatric ECMO samples due to concomitant FVIII increase. Discordant changes of CRP and FVIII in plasma could contribute to aPTT/anti-Xa discrepancies observed during heparin therapy in the pediatric population. The anti-Xa assay is preferable for heparin monitoring in pediatric ECMO settings.

Enoxaparin Dosing and AntiXa Monitoring in Specialty Populations: A Case Series of Renal-Impaired, Extremes of Body Weight, Pregnant, and Pediatric Patients

The use of enoxaparin in specialty populations-including those with renal dysfunction, extremeness of body weight, pregnant patients, and pediatric patients-has not been studied in clinical trials. Monitoring anti-factor Xa activity (antiXa) as a surrogate to measure the activity of enoxaparin may be of interest. A case series of patients admitted to New York University Langone Health between December 2012 and July 2014 who received at least three consecutive doses of enoxaparin for the treatment of VTE and had a peak antiXa level drawn at steady state were evaluated. Patients were included if they were ≤ 18 years of age or if they were > 18 years of age and met one of the following criteria: pregnant, creatinine clearance (CrCl) ≤ 50 ml/min at the time of initiation of enoxaparin, or had a body weight ≤ 50 kg or ≥ 120 kg. A total of 31 patients were included in the analysis. The percentage of patients who achieved a therapeutic antiXa level (0.5-1.2 IU/mL for twice daily enoxaparin or 1-2 IU/mL for once daily enoxaparin) at the time of the first antiXa level drawn was greatest for the adult patients; however, the patients with renal impairment and low body weight were more likely to be sub-therapeutic at first antiXa level check. In addition, neonates and young children required increased enoxaparin doses to achieve therapeutic antiXa. Optimal dosing of enoxaparin in specialty populations has not been established. Furthermore, higher initial doses of enoxaparin may be needed in pediatric patients to attain therapeutic antiXa levels.

Recurrent unprovoked venous thromboembolism in a young female patient with high levels of homocysteine

Hyperhomocysteinemia is a rare condition which predisposes to atherothrombosis. Recurrent venous thromboembolism (VTE) with hyperhomocysteinemia is known but extremely uncommon. Homocysteine levels of more than 22 umol/L can predispose to VTE in a middle-aged women. We describe a case of a middle-aged woman, community ambulant with recurrent VTE with intermediately high homocysteine levels. She had no other risk factors for recurrent venous thrombosis. In our article, we also discuss hyperhomocysteinemia and its link to VTE.

Utilization of coagulation assays in clinical therapeutics

With the emergence of new anticoagulants, clinicians need a thorough understanding of coagulation assays. Various laboratory assays exist to measure the effectiveness of anticoagulants. Coagulation assays are the primary method for measuring the effectiveness of anticoagulants; therefore, a comprehensive understanding of the various assays is critical to interpret the results appropriately. Coagulation test results can be affected by multiple factors including diseases, drugs, and genetic variations. This article reviews the indications, limitations, and interpretation of coagulation assays.