Accuracy, reproducibility and costs of different laboratory assays for the monitoring of unfractionated heparin in clinical practice: a prospective evaluation study and survey among Swiss institutions

Anti-Xa testing for pediatric and neonatal patients on extracorporeal membrane oxygenation

INTRODUCTION

To determine if anti-Xa testing is associated with improved outcomes for patients <19-years-old on ECMO.

METHODS

We evaluated the clinical benefit of anti-Xa heparin monitoring utilizing the Bleeding and Thrombosis during ECMO (BATE) database of 514 patients <19-years-old. The BATE database includes incidences of bleeding, thrombosis, and mortality. The database also describes anti-coagulation test utilization. We grouped and analyzed patients based on ECMO indication (cardiac, respiratory, or extracorporeal cardiopulmonary resuscitation [E-CPR]) and age (neonatal vs pediatric). We constructed multivariable logistic regression models to analyze the impact of anti-Xa testing on mortality, bleeding, and thrombosis in each group.

RESULTS

Across the entire population, anti-Xa testing did not have a significant effect on the incidence of mortality (43% with anti-Xa testing vs 49% without), bleeding (68% vs 74%), or thrombosis (37% vs 39%). However, among cardiac indicated patients on ECMO (n = 207), anti-Xa testing was significantly associated with reduced odds ratio (OR) of mortality (adjusted OR 0.527, p = .040) and bleeding (adjusted OR 0.369, p = .021). In addition, among neonatal patients on ECMO (n = 264), anti-Xa testing was associated with a significant reduction in the odds ratio of bleeding (adjusted OR 0.534, p = .046).

CONCLUSION

Anti-Xa testing is associated with improved outcomes among cardiac indicated and neonatal patients on ECMO. Additional research to find the optimal heparin monitoring regimen is needed to better support these critically ill patients. In the interim, we recommend clinicians consider utilizing anti-Xa assays as part of their heparin monitoring plan for neonatal and cardiac indicated patients on ECMO.

Monitoring anti-Xa Levels to Optimize Low-Molecular-Weight-Heparin Thromboprophylaxis in High-Risk Hospitalized Patients: A Stratified Meta-Analysis

It is uncertain whether monitoring or targeting anti-Xa levels is necessary when using low-molecular-weight-heparin (LMWH) to prevent venous thromboembolism (VTE). This stratified meta-analysis assessed whether monitoring trough or peak anti-Xa levels with LMWH dosing would reduce risk of VTE. Twelve non-randomized studies involving 3604 hospitalized patients met the inclusion criteria and were subject to meta-analysis. Eight studies assessed the association between VTE and peak anti-Xa levels (between .2 and .5 IU/ml) and four studies assessed the benefits of targeting the trough anti-Xa levels (>.1 IU/ml). Achieving an adequate peak or trough anti-Xa level was associated with a reduced risk of VTE (random-effects model odds ratio [OR] .52, 95% confidence interval [CI] .34-.77; P = .001, I2 = 30% and P-value for heterogeneity = .171) compared with using a fixed standard dose of LMWH. Targeting the trough level (OR .40, 95%CI 0.22-.75, P = .004) appeared to be more effective than targeting the peak level (OR .62, 95%CI 0.37-1.03, P = .066), although a formal interaction analysis did not confirm they were statistically different (ratio of ORs = 1.52, 95%CI 0.68-3.40; z score = 1.03, P = .306). Targeting a higher anti-Xa level did not appear to increase the risk of bleeding or transfusion (OR 1.20, 95%CI 0.46-3.17, P = .707).

Chromogenic and Clot-Based Bivalirudin Assays for Monitoring Anticoagulation

BACKGROUND

Direct thrombin inhibitors (DTIs) are usually monitored with the activated partial thromboplastin time (aPTT) or activated clotting time (ACT). Both are complex assays with multiple enzymatic steps, and performance may be influenced by physiologic and pathologic factors unrelated to the DTI. Simpler systems, such as clot-based dilute thrombin time (dTT) and chromogenic anti-factor IIa assays, have been developed for monitoring DTIs, but there is limited data on their performance in clinical settings.

METHODS

Medical records of patients who received bivalirudin between March 2020 and April 2022 at a single institution were reviewed for demographic data and adverse outcomes. Plasma samples drawn for aPTT testing were analyzed with chromogenic anti-IIa and dTT bivalirudin assays. Results were compared to bivalirudin dosing.

RESULTS

Results of aPTT assays from 32 patients were compared with the chromogenic (n = 136) and dTT (n = 120) bivalirudin assays. Correlations between the aPTT and the chromogenic and dTT assays were poor (Spearman coefficients 0.55 and 0.62, respectively). There was a stronger correlation when results of the chromogenic and dTT assays were compared to each other (Spearman coefficient 0.92). When assay results were compared to bivalirudin dose, there were stronger correlations with the chromogenic and dTT assays than with the aPTT (Spearman coefficients 0.51, 0.63 and 0.22, respectively).

CONCLUSIONS

There was considerable variation between results of specific bivalirudin assays and the aPTT. While bivalirudin assay results correlated better with administered drug dose, suggesting improving reliability, more studies are needed to determine if there is correlation between testing and clinical outcomes.

Laboratory Assessment of Unfractionated Heparin (UFH) with Activated Clotting Time (ACT) and Anti-Xa Activity during Peripheral Arterial Angiographic Procedure

Activated clotting time (ACT) is used in cardiac surgery for monitoring unfractionated heparin (UFH). In endovascular radiology, ACT use is less established. We aimed to test the validity of ACT in UFH monitoring in endovascular radiology. We recruited 15 patients undergoing endovascular radiologic procedure. ACT was measured with ICT Hemochron^® device as point-of-care (1) before standard UFH bolus, (2) immediately after the bolus, and in some cases (3) 1 h into the procedure or a combination thereof (altogether 32 measurements). A total of two different cuvettes, ACT-LR and ACT+ were tested. A reference method of chromogenic anti-Xa was used. Blood count, APTT, thrombin time and antithrombin activity were also measured. UFH levels (anti-Xa) varied between 0.3-2.1 IU/mL (median 0.8) and correlated with ACT-LR moderately (R² = 0.73). The corresponding ACT-LR values were 146-337 s (median 214). ACT-LR and ACT+ measurements correlated only modestly with one another at this lower UFH level, with ACT-LR being more sensitive. Thrombin time and APTT were unmeasurably high after the UFH dose, rendering them of limited use in this indication. We adopted an ACT target of >200-250 s in endovascular radiology based on this study. While ACT correlation with anti-Xa is suboptimal, the readily available point-of-care nature increases its suitability.

Validation of high concentrated thrombin time assay for unfractionated heparin monitoring

Background

The high concentrated thrombin time (hcTT), a thrombin time modified by increasing the thrombin concentration, is a possible alternative assay to activated partial thromboplastin time (aPTT) in unfractionated heparin (UFH) monitoring. This study aimed to determine the optimal thrombin concentration used in the hcTT assay for UFH monitoring.

Methods

A total of 30 blood samples obtained from healthy volunteers were included in this study. Thrombin concentrations of 10.0, 15.0, 20.0, and 25.0 IU/ml were used in the hcTT assay. The consistency between the hcTT and anti‐FXa assays was evaluated. To validate the hcTT assay, linearity, repeatability, reproducibility, and diagnostic performance of the assay were assessed.

Results

The hcTT assay using thrombin concentration of 15.0 IU/ml showed a strong correlation to the anti‐FXa assay with R² of 0.72 and the Spearman's correlation coefficient (r_s) of 0.97 (95% CI, 0.96–0.98). Within‐run and day‐to‐day run variabilities of the assay were satisfactory (all coefficients of variation <10%). We found an excellent correlation between the results which were measured using different reagents with intra‐ or inter‐laboratory instruments. Notably, as compared to the aPTT assay, the hcTT assay showed a significantly better performance in identifying the samples which contain UFH at the supratherapeutic level, with an AUC of 0.97 vs. 0.91, p = 0.049.

Conclusion

The hcTT assay can be used as an alternative assay for UFH therapy monitoring. A further study using clinical samples is recommended to confirm the appropriateness of the hcTT assay for clinical application.

Prothrombinase-Induced Clotting Time to Measure Drug Concentrations of Rivaroxaban, Apixaban, and Edoxaban in Clinical Practice: A Cross-Sectional Study

Prothrombinase-induced clotting time (PiCT) is proposed as a rapid and inexpensive laboratory test to measure direct oral anticoagulant (DOAC) drug levels. In a prospective, multicenter cross-sectional study, including 851 patients, we aimed to study the accuracy of PiCT in determining rivaroxaban, apixaban, and edoxaban drug concentrations and assessed whether clinically relevant drug levels could be predicted correctly. Citrated plasma samples were collected, and the Pefakit^® PiCT was utilized. Ultra-high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed to measure drug concentrations. Cut-off levels were established using receiver-operating characteristics curves. We calculated sensitivities and specificities with respect to clinically relevant drug concentrations. Spearman’s correlation coefficient between PiCT and drug concentrations was 0.85 in the case of rivaroxaban (95% CI 0.82, 0.88), 0.66 for apixaban (95% CI 0.60, 0.71), and 0.78 for edoxaban (95% CI 0.65, 0.86). The sensitivity to detect clinically relevant drug concentrations was 85.1% in the case of 30 µg L⁻¹ (95% CI 82.0, 87.7; specificity 77.9; 72.1, 82.7), 85.7% in the case of 50 µg L⁻¹ (82.4, 88.4; specificity 77.3; 72.5, 81.5), and 85.1% in the case of 100 µg L⁻¹ (80.9, 88.4; specificity 73.2%; 69.1, 76.9). In conclusion, the association of PiCT with DOAC concentrations was fair, and the majority of clinically relevant drug concentrations were correctly predicted.

Improving safety of unfractionated heparin: a retrospective, quasi-experimental, observational study of the impact of a pocket card and a computerised prescription aid tool in the University Hospitals of Geneva

BACKGROUND

Despite the rapid rise of direct oral anticoagulants, unfractionated heparin (UFH) remains the mainstay anticoagulant in specific situations such as severe renal failure, perioperative setting or in critical care units. However, its titration is often challenging.

OBJECTIVES

To investigate the effect of a pocket card and a computerised prescription aid tool (CPAT) on the quality of UFH anticoagulation.

DESIGN

Monocentric retrospective, quasi-experimental, observational study.

SETTING

Inpatient primary care centre between 1 January 2016 and 31 December 2019.

PARTICIPANTS

>18 years-old treated with therapeutic UFH for more than 24 hours. There were 819 and 1169 anticoagulation episodes before and after intervention, respectively.

INTERVENTION

In October 2017, we implemented a pocket card with evidence-based recommendation for therapeutic UFH initiation, monitoring and dosing adaptation. In October 2019, we implemented a CPAT in a group subset.

PRIMARY AND SECONDARY OUTCOMES

The primary outcome was the time needed to reach a therapeutic anti-Xa before and after the implementation of the pocket card. The secondary outcomes included a subgroup analysis assessing the effect of the CPAT. Other secondary outcomes were the anti-Xa status (infratherapeutic, therapeutic or supratherapeutic) at 7 and 24 hours of UFH treatment.

RESULTS

We found a significant increase in the time to reach therapeutic dosing with pocket card-guided recommendations implementation (10.1 vs 14 hours, HR of 0.8, 95% CI: 0.70 to 0.93). However, the CPAT was associated with a significant decrease in the time needed to reach the therapeutic range (13.9 vs 7.1 hours, HR of 1.74, 95% CI: 1.17 to 2.60).

CONCLUSION

Although we observed an increase in time to reach therapeutic anti-Xa with the pocket card, possibly due to a selection bias (use of activated partial thromboplastin time for monitoring before the pocket card), the implementation of CPAT significantly decreased the delay for effective therapy. Further studies are needed to confirm these findings, and to determine the optimal initial dose of UFH anticoagulation.

Optimization of Heparin Monitoring with Anti-FXa Assays and the Impact of Dextran Sulfate for Measuring All Drug Activity

Heparins, unfractionated or low molecular weight, are permanently in the spotlight of both clinical indications and laboratory monitoring. An accurate drug dosage is necessary for an efficient and safe therapy. The one-stage kinetic anti-FXa assays are the most widely and universally used with full automation for large series, without needing exogenous antithrombin. The WHO International Standards are available for UFH and LMWH, but external quality assessment surveys still report a high inter-assay variability. This heterogeneity results from the following: assay formulation, designed without or with dextran sulfate to measure all heparin in blood circulation; calibrators for testing UFH or LMWH with the same curve; and automation parameters. In this study, various factors which impact heparin measurements are reviewed, and we share our experience to optimize assays for testing all heparin anticoagulant activities in plasma. Evidence is provided on the usefulness of low molecular weight dextran sulfate to completely mobilize all of the drug present in blood circulation. Other key factors concern the adjustment of assay conditions to obtain fully superimposable calibration curves for UFH and LMWH, calibrators' formulations, and automation parameters. In this study, we illustrate the performances of different anti-FXa assays used for testing heparin on UFH or LMWH treated patients' plasmas and obtained using citrate or CTAD anticoagulants. Comparable results are obtained only when the CTAD anticoagulant is used. Using citrate as an anticoagulant, UFH is underestimated in the absence of dextran sulfate. Heparin calibrators, adjustment of automation parameters, and data treatment contribute to other smaller differences.

A universal anti-Xa assay for rivaroxaban, apixaban, and edoxaban measurements: method validation, diagnostic accuracy and external validation

A universal anti‐Xa assay for the determination of rivaroxaban, apixaban and edoxaban drug concentrations would simplify laboratory procedures and facilitate widespread implementation. Following two pilot studies analysing spiked samples and material from 698 patients, we conducted a prospective multicentre cross‐sectional study, including 867 patients treated with rivaroxaban, apixaban or edoxaban in clinical practice to comprehensively evaluate a simple, readily available anti‐Xa assay that would accurately measure drug concentrations and correctly predict relevant levels in clinical practice. Anti‐Xa activity was measured by an assay calibrated with low‐molecular‐weight heparin (LMWH) in addition to ultra‐high performance liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). As an external validation, LMWH‐calibrated anti‐Xa activity was also determined in nine external laboratories. The LMWH‐calibrated anti‐Xa activity correlated strongly with rivaroxaban, apixaban or edoxaban drug levels [r_s = 0·98, 95% confidence interval (CI) 0·98–0·98]. The sensitivity for the clinically relevant cut‐off levels of 30, 50 and 100 µg/l was 96·2% (95% CI 94·4–97·4), 96·4% (95% CI 94·4–97·7) and 96·7% (95% CI 94·3–98·1) respectively. Concordant results were obtained in the external validation study. In conclusion, a universal, LMWH‐calibrated anti‐Xa assay accurately measured rivaroxaban, apixaban and edoxaban concentrations and correctly predicted relevant drug concentrations in clinical practice.

Cartridge-Based Thromboelastography Can Be Used to Monitor and Quantify the Activity of Unfractionated and Low-Molecular-Weight Heparins

Thromboelastography is increasingly utilized in the management of bleeding and thrombotic complications where heparin management remains a cornerstone. This study assessed the feasibility of the cartridge-based TEG ^® 6s system (Haemonetics Corp., Braintree, Massachusetts, United States) to monitor and quantify the effect of unfractionated and low-molecular-weight heparin (UFH and LMWH). Blood samples from healthy donors were spiked with UFH ( n  = 23; 0–1.0 IU/mL) or LMWH (enoxaparin; n  = 22; 0–1.5 IU/mL). Functional fibrinogen maximum amplitude (CFF.MA), RapidTEG activated clotting time (CRT.ACT), and kaolin and kaolin with heparinase reaction time (CK.R and CKH.R) were evaluated for their correlation with heparin concentrations, as well as the combination parameters ΔCK.R − CKH.R, ratio CK.R/CKH.R, and ratio CKH.R/CK.R. Nonlinear mixed-effect modelling was used to study the relationship between concentrations and parameters, and Bayesian classification modelling for the prediction of therapeutic ranges. CK.R and CRT.ACT strongly correlated with the activity of LMWH and UFH ( p  < 0.001). Using combination parameters, heparin activity could be accurately quantified in the range of 0.05 to 0.8 IU/mL for UFH and 0.1 to 1.5 IU/mL for LMWH. CRT.ACT was able to quantify heparin activity at higher concentrations but was only different from the reference range ( p  < 0.05) at >0.5 IU/mL for UFH and >1.5 IU/mL for LMWH. Combination parameters classified blood samples into subtherapeutic, therapeutic, and supratherapeutic heparin ranges, with an accuracy of >90% for UFH, and >78% for LMWH. This study suggests that TEG 6s can effectively monitor and quantify heparin activity for LMWH and UFH. Additionally, combination parameters can be used to classify blood samples into therapeutic ranges based on heparin activity.