Markers of hypercoagulability in children with newly diagnosed acute lymphoblastic leukemia.

BACKGROUND: Venous thromboembolism (VTE) is a known complication for children with acute lymphoblastic leukemia (ALL). The aim of this study was to identify laboratory biomarkers that predict which children with ALL are at risk for VTE during induction chemotherapy. MATERIALS AND METHODS: Newly diagnosed ALL patients admitted to Children's Hospital Los Angeles with a central venous catheter (CVC) were eligible to participate. Participants' blood samples (complete blood count [CBC], quantitative D-dimer, prothrombin fragment 1.2 [PTF 1.2], and thrombin-antithrombin complexes [TAT]) were collected at day 0 (baseline/prior to induction), day 7 (±2 days), day 14 (±2 days), day 21 (±2 days), and day 28 (±2 days) of induction chemotherapy or until participants presented with a symptomatic VTE. RESULTS: Seventy-five participants aged 1-21 years were enrolled and included in the final analysis. Twenty-six (35%) of the 75 participants were diagnosed with a CVC-associated VTE (22 asymptomatic and four symptomatic). There was a statistically significant difference between VTE and non-VTE participants for D-dimer (odds ratio [OR] 1.61, 95% confidence interval [CI]: 1.59-1.64), TAT (OR 1.34, 95% CI: 1.32-1.38), and PTF 1.2 (OR 1.31, 95% CI: 1.25-1.37) at all time points. Participants >10 years had a significantly higher risk of developing a VTE compared to participants <4 years (p = .007). CONCLUSION: Older children with ALL as well as those with an elevated TAT, PTF 1.2, or D-dimer showed an increased risk of VTE, which may hold potential for predicting VTE in future studies.

Determining the approximate factor VIII level of patients with severe haemophilia A on emicizumab using in vivo global haemostasis assays.

INTRODUCTION: Emicizumab is a recombinant, humanized bispecific monoclonal antibody that mimics the function of factor VIII (FVIII) which results in a significant reduction in the annualized bleeding rate in patients with haemophilia A (HA), however, the degree with which emicizumab corrects the coagulation defect remains unclear. The objective of this study was to predict the approximate FVIII level in severe haemophilia A patients with inhibitors on emicizumab using global haemostasis assays. MATERIALS AND METHODS: Patients with moderate and mild HA in the non-bleeding state and healthy controls had FVIII levels and thrombin generation assessed. Linear regression was utilized to model the FVIII levels as a function of the thrombin generation assay parameters and to make a calibration curve of FVIII levels versus peak thrombin and endogenous thrombin potential. Patients with severe haemophilia A with inhibitors on emicizumab had thrombin generation performed in the same manner and their peak thrombin and endogenous thrombin potential results were placed on the calibration curve to calculate their FVIII Equivalency of Emicizumab by Thrombin Generation (F8EmT). RESULTS: All patients with severe HA with inhibitors on emicizumab had F8EmT >10%, suggesting they had been converted to a mild haemophilia phenotype. The patient's weight was inversely correlated to their F8EmT. CONCLUSION: The results from this study suggest that the F8EmT in patients with severe HA on emicizumab falls within the range of mild haemophilia which is consistent with the data noted in the emicizumab clinical trials and in vivo studies in animals.

Comparison of bypassing agents in patients on emicizumab using global hemostasis assays.

INTRODUCTION: Emicizumab is a humanized bispecific monoclonal antibody licensed for patients with severe haemophilia A with and without inhibitors. Management of breakthrough bleeding in patients with inhibitors on emicizumab involves episodic treatment with bypassing agents (BPA), activated prothrombin complex concentrate (aPCC) or recombinant activated factor VII (rFVIIa). Thrombotic events and thrombotic microangiopathy were reported when patients on emicizumab received concomitant aPCC at relatively high doses yet such events were not reported with rFVIIa. We studied the effect of spiking various concentrations of BPA on plasma taken from patients on emicizumab. MATERIAL AND METHODS: Eleven patients with severe haemophilia A with inhibitors who are on emicizumab were recruited to participate. Blood samples drawn from patients were spiked in vitro with varying concentrations of aPCC and rFVIIa. All samples were tested utilizing global haemostasis assays, thromboelastography and thrombin generation assay. RESULTS: Thrombin generation increased with higher concentrations of spiked BPA with a normalized endogenous thrombin potential at a concentration of 0.05 IU/ml and 4 mcg/ml for aPCC and rFVIIa, respectively. Concentrations of aPCC in the range of licensed dosing led to excessive thrombin generation. Thromboelastography was not sufficiently sensitive. CONCLUSION: Due to the known thrombotic complications when emicizumab is used in conjunction with aPCC, there has been a large-scale abandonment of the use of aPCC in patients on emicizumab. However, it is possible that aPCC can be used safely with emicizumab albeit with lower doses than are typically prescribed. It would be important to test this hypothesis in a clinical study.

Thromboelastography and thrombin generation assay in inherited afibrinogenemia.

Fibrinogen is a glycoprotein with a crucial role in blood coagulation. Upon enzymatic cleavage by thrombin, fibrinogen is converted from its soluble form to insoluble fibrin which is key structural protein of a clot. It also participates in platelet aggregation by binding to GPIIb/IIIa. Genetic alterations can lead to either complete or partial, quantitative or qualitative defects of fibrinogen. Inherited afibrinogenemia is a rare bleeding disorder with autosomal recessive inheritance due to a complete absence of fibrinogen. The primary aim of this study was to determine whether 70 mg/kg of human fibrinogen concentrate (HFC) is an adequate dose in subjects with inherited afibrinogenemia to reach normal levels of plasmatic fibrinogen (1.5-2 g/L). Secondary aims included assessing changes in thromboelastography (TEG) and thrombin generation assay (TGA) before and after a dose of HFC. Four patients were included, and each underwent pre-and post (one time-point) HFC dose laboratory testing. Two patients needed dose adjustments to reach a normal post-dose fibrinogen level. In addition, we noted that the TEG parameter maximum amplitude (MA) improved in accordance with correction of the fibrinogen levels. TGA results were normal in all subjects. Our results suggest that individualized dosing based on fibrinogen levels may be necessary.

Obesity and risk for venous thromboembolism from contemporary therapy for pediatric acute lymphoblastic leukemia.

INTRODUCTION: Acute lymphoblastic leukemia (ALL) therapy confers risk for venous thromboembolism (VTE) and associated acute and long-term morbidity. Obesity increases VTE risk in the general population but its impact on ALL therapy-associated VTE is unknown. METHODS: In a retrospective cohort of children treated for ALL between 2008 and 2016 (n = 294), we analyzed obesity at diagnosis (body mass index [BMI] ≥95%) and subsequent development of VTE. A subset participated in two concurrent prospective ALL trials studying body composition via dual-energy X-ray absorptiometry (DXA) (n = 35) and hypercoagulability via thromboelastography (TEG) (n = 46). Secondary analyses explored whether precise measurement of body fat and/or global hemostasis ex vivo by TEG could further delineate VTE risk in the obese. RESULTS: Overall, we found 27/294 (9.2%) patients developed symptomatic VTE during therapy, 19/27 (70%) occurred during Induction. Study-defined "serious" VTE developed in 4/294 (1.4%) of patients. Obesity but not overweight was strongly predictive of symptomatic VTE (obesity odds ratio = 3.8, 95% confidence interval 1.5-9.6, p = 0.008). In the DXA subset, only 2/35 patients developed symptomatic VTE. However, within those prospectively screened during Induction, 30% (14/46) developed VTE; eight (17%) of these were asymptomatic and found only via screening. CONCLUSIONS: In this pediatric ALL cohort, obesity conferred more than a three-fold increased risk for symptomatic VTE. In a subgroup of patients who underwent active screening, up to a third were noted to have VTE (symptomatic and asymptomatic). TEG did not predict VTE. Additional studies are necessary to validate these findings and to further refine a risk-stratified approach to thrombo-prevention during ALL therapy.

Thromboelastographic characterization of the activated clotting system in children with sickle cell trait or sickle cell disease.

BACKGROUND: Recent epidemiological evidence suggests sickle cell disease (SCD) and sickle cell trait (SCT) is a risk factor for venous thromboembolism. The increased in-vivo markers of thrombin generation support the notion that such patients are in a chronic hypercoagulable state. In an attempt to better understand the underlying mechanism, global hemostatic assays including thrombin generation assay (TGA) and thromboelastography (TEG) have been utilized by several groups, but thus far, have shown inconsistent results either due to small sample size or technical differences. OBJECTIVES: Global hemostatic characterization of children with SCD or SCT by using TGA and modified TEG methods. MATERIALS AND METHODS: In this pilot study, we obtained TGA, TEG and other hemostatic data on specimens from 13 patients with SCD, 14 with SCT and 12 race-matched healthy controls (NC). RESULTS: R time and K time with modified TEG methods were significantly shorter in SCD when compared to SCT and NC. Alpha and MA did not show any significant differences between the groups. There was no difference seen between SCT and NC. TGA profiles did not show any difference between the three groups. As expected the in-vivo markers of thrombin generation and activation of fibrinolysis including D dimer and thrombin-antithrombin complexes were significantly higher in SCD subjects as compared to SCT and NC. CONCLUSION: The modified TEG methods are able to detect the activated coagulation system for the SCD population but a larger and more homogenous SCT cohort needs to be studied for more conclusive results.