Thrombin Generation In Children Research Articles

Bleeding phenotype and hemostatic evaluation by thrombin generation in children with Noonan syndrome: A prospective study.

This study aimed to evaluate the bleeding phenotype and to conduct a comprehensive hemostatic evaluation in individuals with Noonan syndrome (NS), a dominantly inherited disorder caused by pathogenic variants in genes associated with the Ras/MAPK signaling pathway. Children with a genetically confirmed diagnosis of NS underwent clinical evaluation, routine laboratory tests, platelet function testing, and thrombin generation (TG) assessment. The study included 24 children. The most frequently reported bleeding symptoms were easy bruising and epistaxis, while bleeding complications were observed in 15% of surgical procedures. Various hemostatic abnormalities were identified, including platelet dysfunction, von Willebrand disease, and clotting factor deficiencies. Abnormal platelet function was observed in 50% of the patients, and significantly lower TG parameters were found compared to controls. However, no significant correlation was observed between bleeding symptoms and TG results. The study suggests that the bleeding diathesis in NS is multifactorial, involving both platelet dysfunction and deficiencies of plasma coagulation factors. The potential role of TG assay as an ancillary tool for predicting bleeding tendencies in individuals with NS undergoing surgery warrants further investigation.

Hemostatic Profile at Diagnosis in Childhood Acute Lymphoblastic Leukemia: A Meta-Analysis of Cases from the Literature

Introduction Acute lymphoblastic leukemia (ALL) is the most common type of childhood cancer with, an incidence rate of 7.55 cases per 100,000 person-years for males aged 0-4 in the Canadian population. Thromboembolism (TE) is a well-recognized serious complication associated with ALL that results in significant morbidity and occasionally mortality. In patients with ALL, the reported incidence of symptomatic and asymptomatic TE is as high as 16% and 37%, respectively. At diagnosis, there is evidence of increased thrombin generation in children with ALL. Patients often present with a hypercoagulable state and this prothrombotic condition persists during the treatment period, indicating a possible interaction of the disease and therapy. Since the efficacy and safety of thromboprophylaxis during ALL treatment are still being explored, understanding the biology of the disease is crucial for defining the optimal strategy for prevention and management of ALL-associated thrombosis. In this study, we aim to explore a better understanding of how ALL affects the hemostatic balance. Due to the low incidence of leukemia, single-center studies are not adequately powered to detect significance. This meta-analysis was conducted to comprehensively evaluate the hemostatic profile at the time of diagnosis in pediatric ALL patients. Method PubMed database was searched on December 2021 with the following keywords: "acute lymphoblastic leukemia", "coagulation", "fibrinolysis" and "hemostatic." The inclusion criteria were: 1) study participants with childhood ALL, 2) hemostatic parameters were measured and reported at the time of diagnosis, 3) there is a comparator group of healthy subjects, and 4) there is no other reported comorbidities. Non-human studies, non-English articles and studies without healthy comparators were excluded. Data on coagulation profile at diagnosis were collected and meta-analyzed. The statistical method was random-effect inverse-variance weighting. The results were reported as mean difference with 95% confidence intervals (CIs) Result The initial search yielded 643 articles. Of these, 505 studies were excluded from title/abstract screening. The fulltexts of the remaining studies were screened, and 33 studies were included for the final analysis. D-dimer levels were elevated in the Leukemic group by 533.73 ng/ml [95% CIs: 283.1-782.35], p<0.01, n=216,193. Thrombin-antithrombin complex levels were also increased in the Leukemic group by 109.89 ug/L [95% CIs: 77.89-141.89], p<0.01, n=149,136. In addition, the levels of natural anticoagulants were reduced in the Leukemic group. Protein C activities were lower in the Leukemic group by 20.29% [95% CIs: 2.14-38.44], p<0.01, n=146,115. Protein S activities were lower in the Leukemic group by 29.11% [95% CIs: -1.28-59.5], p<0.01, n=146,115. Furthermore, markers of endothelial dysfunction were elevated in the Leukemic group. VWF levels were increased by 28.26% [95% CIs: -1.64-58.17], p<0.01, n=133,205 while tPA levels were reduced by 631.15 pg/ml [95% CIs: 296.22-966.09], p<0.01, n=122,80. Significance Children with ALL already present with hemostatic imbalance at diagnosis, favoring a hypercoagulable state. Interestingly, there has been little research on thrombin markers prior to chemotherapy in childhood ALL. The majority of data were extracted from prospective studies investigating the effect of therapy on thrombosis. Our study highlights significant differences from healthy control levels in D-dimer, Thrombin-antithrombin complex, protein C activity, protein S activity, VWF and tPA levels in children with ALL at diagnosis. Better tools of prediction would allow prospective identification of patients in whom prophylaxis might reduce the risk of thrombosis. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Thrombin generation in children using ThromboScreen reagent kit with ST Genesia—A pilot study

Thrombin generation assays assess overall coagulation system and are widely used in research; however, they still need standardization and clinical validation. The new ST Genesia is a benchtop, automated analyzer that normalizes each thrombin generation parameter using a reference plasma. The ThromboScreen reagent kit has two triggers, one of which contains thrombomodulin to assess the effect of the protein C pathway. This study aimed to make a pilot approach to the ThromboScreen reference range in children and evaluate the impact of sex, age, and pro- and anticoagulant plasma proteins on thrombin generation parameters. This study included 55 healthy children from the following age groups: 1-6years (n=14), 7-11years (n=15), and 12-17years (n=26). Children younger than 1year were excluded from the study. We measured thrombin generation using ThromboScreen, coagulation routine and test, pro- and anticoagulant proteins. Age did not influence ThromboScreen results. Males showed significantly lower endogenous thrombin potential and peak height values than females. The strongest determinants of endogenous thrombin potential were von Willebrand factor parameters, whereas for endogenous thrombin potential inhibition, the strongest determinants were protein C and protein S. No statistically significant differences were found betweengroups on temporal parameters. For the ThromboScreen reagent kit, it may not be necessary to subdivide reference ranges according to age for children (>1year).

Thrombin generation in children with febrile neutropenia.

Febrile neutropenia (FN) is a common and serious complication in patients with leukemia. Hemostasis and inflammation are two interrelated systems in response to infection. We aimed to investigate the course of thrombin formation in febrile neutropenia attack of children with acute lymphoblastic leukemia (ALL). Thrombin generation was monitored in children treated for ALL at diagnosis of febrile neutropenia (FN) (t < sub > 0 < /sub > ), at 48 < sup > th < /sup > hour of FN (t1) and after recovery from neutropenia (t < sub > 2 < /sub > ). Twenty-nine patients and 50 healthy children as control were enrolled into the study. Mean endogenous thrombin potential (ETP) and mean peak value of thrombin results at t < sub > 1 < /sub > were significantly higher than at t < sub > 0 < /sub > , t < sub > 2 < /sub > and control groups, respectively. A positive but statistically nonsignificant correlation between ETP values at t < sub > 1 < /sub > and duration of neutropenia was observed. Although thrombin generation is enhanced both due to chemotherapy or malignancy itself, our results revealed that thrombin formation also increased in neutropenic infection of children with leukemia.

Thrombin generation in children with sickle cell Anemia is Higher in the presence of platelets⋆ and ⋆

Cellular and plasma interactions underlie hypercoagulability in sickle cell anemia (SCA). In healthy adults, thrombin generation (TG), a biomarker of hypercoagulability, is similar in plasma with and without platelets. Studies investigating TG in SCA using platelet-poor plasma (PPP) show conflicting results. There are no studies in SCA simultaneously comparing TG using platelet rich plasma (PRP) and PPP.This prospective study compares TG in children with SCA, at steady state, in PPP versus PRP and investigates the association of predefined clinical variables with the difference between PRP and PPP. Our secondary aim was to investigate derangements in the protein C and S pathway measuring TG with and without thrombomodulin (TM).In forty-three paired samples from SCA patients, aged 2−15 years, TG in the presence of platelets was 5.9 % higher [1239 nmol/(min*L) (SD: 224.1) vs. 1151 nmol/(min*L) (SD 223.3); p = 0.026]. The difference was highest in the 6−10 year age group (9.5 %; SD 14.1) followed by the 2−5 year age group (5.4 %; SD 21.4). In a multiple linear regression model, age, gender, current use of hydroxyurea, degree of hemolysis and severity of pain crises were not predictive of the difference between PRP and PPP. In PPP, TG reduction after TM addition was 7.4 % (SD 16.8), signifying activated protein C resistance.In conclusion, TG in children with SCA aged 2−10 years is higher in the presence of platelets. TG using PRP along with TM addition may be a useful biomarker of hypercoagulability in this population.

Thrombin lag time is increased in children with mild asthma

BackgroundInflammation and coagulation are closely linked events. Thrombin is the key enzyme in coagulation system and also has roles in inflammation. ObjectiveThe aim of our study was to evaluate thrombin generation in children with mild asthma. MethodsForty-two children with mild asthma and 49 healthy children were included in the study. All patients performed spirometry. Thrombin generation tests (TGT) were performed with a calibrated automated thrombogram (CAT) in children without asthma exacerbation during the last six months. During CAT assay thrombogram curves were obtained. The area under the curve showed endogenous thrombin potentials and indicated the total amount of endogenous thrombin generated; the peak height showed the highest thrombin value, thrombin lag time and time to thrombin peak were measured. ResultsThrombin lag time was significantly longer in children with asthma (3.98±1.2min) compared to those in the control group (3.29±0.6min) (p<0.01). Children with asthma also had longer thrombin tail time compared to the control group (19.5±8.9min vs. 16.7±2.9min, p=0.02). Thrombin peak was inversely correlated with FEF 25–75 (r=−0.41, p<0.01). Thrombin lag time was inversely correlated with FEF 25–75 (r=−0.39, p<0.01). ConclusionInflammation in mild asthma seems to disturb coagulation but this disturbance may not be so strong as to increase thrombin levels and may only affect the initiation phase of thrombin generation.

Only minor changes in thrombin generation of children and adolescents with type 1 diabetes mellitus – A case-control study

BackgroundMicro- and macrovascular diseases are frequent complications in patients with diabetes. Hypercoagulability may contribute to microvascular alterations. ObjectiveIn this study, we investigated whether type 1 diabetes in children is associated with a hypercoagulable state by performing a global function test of coagulation – the thrombin generation assay. Subjects75 patients with type 1 diabetes aged between 2 and 19years were compared to an age-matched healthy control group. Diabetes patients were divided into high-dose and low-dose insulin cohorts with a cut-off at 0.8Ukg−1d−1. MethodsMeasurements were performed with platelet poor plasma using Calibrated Automated Thrombography and 1 pM or 5 pM tissue factor. Additionally, we quantified prothrombin fragments F1+2, thrombin-antithrombin complex, prothrombin, tissue factor pathway inhibitor, and antithrombin. ResultsPatients with type 1 diabetes exhibited a significantly shorter of lag time as well as decreased thrombin peak and endogenous thrombin potential compared to control subjects with 5 pM but not with 1 pM tissue factor. In high-dose insulin patients peak thrombin generation was higher and time to peak shorter than in low-dose patients. Thrombin-antithrombin complex was decreased in patients with type 1 diabetes, whereas prothrombin fragments F1+2 was comparable in both groups. Thrombin generation parameters did not correlate with parameters of metabolic control and the duration of diabetes. ConclusionsTaken together, we found only minor changes of thrombin generation in children and adolescents with type 1 diabetes which - in contrast to type 2 diabetes - do not argue for a hypercoagulable state.

Changes in thrombin generation in children after cardiac surgery and ex-vivo response to blood products and haemostatic agents.

Impaired haemostasis has been reported in children with congenital heart disease undergoing cardiopulmonary bypass. As thrombin generation encompasses all phases of the coagulation process, this analysis might provide the best assessment of global haemostasis. A prospective study was undertaken to test the hypothesis that thrombin generation reveals an impaired haemostasis after paediatric cardiac surgery and that ex-vivo addition of platelet concentrate and haemostatic agents improves thrombin generation. The study comprised 29 children with congenital heart disease, who underwent corrective surgery including cardiopulmonary bypass. Thrombin generation was analysed both in platelet-poor plasma and platelet-rich plasma. Analysis of the thrombin generation showed a significantly prolonged lag time (Pplatelet-poorandplatelet-richplasma < 0.001), decreased peak thrombin generation (Pplatelet-poorplasma = 0.013; Pplatelet-richplasma < 0.001) as well as a decreased endogenous thrombin generation potential (Pplatelet-poorandplatelet-richplasma < 0.001) after cardiopulmonary bypass compared to baseline. Ex-vivo addition of platelet concentrate, fibrinogen concentrate and recombinant factor VIIa improved thrombin generation significantly (all P < 0.001). Changes were most pronounced after addition of platelet concentrate. The present study showed that thrombin generation was significantly reduced after cardiopulmonary bypass in children, both when analysed in platelet-poor and platelet-rich plasma. The impaired haemostasis was not only restored after ex-vivo addition of platelet concentrate but also rVIIa improved the haemostatic capacity.

Thrombin Generation in Children after Acute Venous Thromboembolism

Introduction: Venous thromboembolism (VTE) is a major and growing problem in children. The annual rate of VTE has increased by 70% in the U.S hospitalized children in the past decade. Accompanying this increase in VTE is the attendant increase in chronic, post-thrombotic sequeale of VTE. Strategies to identify children at high risk of developing poor outcomes after initial management of VTE are unclear. We hypothesized that 'global coagulation assessment' may identify children likely to suffer from poor thrombosis outcomes following an initial event. In this pilot study, we therefore, evaluated thrombin generation (TG) after an acute episode of provoked VTE in children. Methods: Baseline patient, thrombus characteristics and thrombophilia testing were prospectively collected for 50 consecutive children with acute, provoked VTE after informed consent. Subjects with cancer, protein C, protein S and antithrombin deficiency, persistent antiphospholipid positivity and inflammatory disorders were excluded. Thrombin generation, using corn trypsin inhibited treated plasma by calibrated automated thrombogram was measured in the presence and absence of thrombomodulin (TM), 4 weeks after completion of anticoagulation therapy, and compared to 50 healthy controls. All cases were treated according to the 9th edition of American College of Chest Physicians Clinical Practice Guidelines. Results: The mean age of VTE cases was 14 years (range: 6 weeks to 18 years). Two thirds (33/50) of VTE cases consisted of deep venous thrombosis of the limbs and/or pulmonary embolism, and nearly 20% (10/50) were cerebral sinovenous thrombosis. Thrombin generation of subjects showed significantly higher endogenous thrombin potential (ETP) compared to healthy controls (1150 ± 281 vs. 763 ± 274 nM.min; p &lt;0.001). There were no significant differences in the other TG parameters (lag time and thrombin peak) between VTE cases and healthy controls. Inhibition by TM was attenuated in patients compared to controls (22% vs. 45.5% p&lt;0.001). A significant negative correlation was found between those with elevated FVIII levels (&gt;150%) at end of therapy and TM induced reduction of ETP (r=0.297 vs. 0.171; p&lt;0.01). In conclusion, a novel finding in children with provoked VTE was persistent elevation of TG after successful completion of anticoagulation therapy. A role for FVIII as an important cause of hypercoagulability after anticoagulation therapy is reflected by the reduced inhibitory effect of TM at high FVIII levels. Further studies are ongoing to determine the utility of TG as a biomarker for predicting poor outcomes after VTE in children. Disclosures Journeycake: CSL, Baxalta, NovoNordisk: Consultancy; ATHN: Research Funding; Biogen: Speakers Bureau; ATHN: Membership on an entity's Board of Directors or advisory committees.

Alpha-2-Macroglobulin Is a Major Determinant Of a Lower Thrombin Generation In Infants and Children Compared To Adults

▪ IntroductionDevelopmental Haemostasis, the concept describing maturation of the haemostatic system is based on established age specific differences in the quantity and function of haemostatic proteins. Interestingly, infants and children have a lower incidence of thromboembolic events than adults. Understanding the precise mechanism of thromboprotection in infants and children may therefore provide novel prevention and treatment strategies for adults. We hypothesized that a significant component of the thromboprotective mechanism is contributed to by the age-specific differences in thrombin generation. AimThis study was designed to investigate differences in thrombin generation in different age groups from infants to adults, to obtain more insight into age related differences in thromboembolic rates. Materials and MethodsPlasma samples from 86 infants, children and adults were tested individually and the results were grouped according to age: 1 month to 1 year (N=13), 1-5 years (N=20), 6-10 years (N=19), 11-16 years (N=16) and adults (N=18). Thrombin generation (TG) was measured using Calibrated Automated Thrombinography (CAT) triggered with tissue factor (TF) at 5pM and 1pM final concentration. Parameters measured from the TG curve included: lag time, maximal thrombin concentration (peak), time to peak, as well as the area under the curve (endogenous thrombin potential, ETP). The raw data from TG was also used to calculate the overall, as well as alpha-2-macroglobulin (A2M) dependent decay constants. A2M function was measured with a thrombin inhibition assay developed in house. ResultsBoth ETP and peak thrombin in infants and children was consistently significantly lower than in adults at both 1pM and 5pM tissue factor concentrations. The difference in ETP ranged from 27% to 35% (p<0.0001), while the difference in peak thrombin generated ranged from 28% to 37% (p<0.005). The thrombin decay constant (total inhibition of thrombin) was 15% (p<0.01) higher in infants and children compared to adults. The A2M-specific decay constant was on average 93% (p<0.001) higher in the younger populations and represented 14% of the total thrombin inhibition, compared to 9% in adults. The functional A2M-levels were 54% (p<0.05) higher in infants and children compared to adults; and correlated significantly with age (r=0.564, p<0.001). Discussion and ConclusionsThis study confirms that TG in children (including adolescents) is lower than in adults and shows for the first time that this is predominantly caused by higher thrombin inhibition, largely due to an increase of A2M activity.Considering that the levels of A2M are increased by 50%, Antithrombin is decreased by approximately 37%, whilst the levels of Prothrombin, Fibrinogen and Heparin Cofactor II remain the same in infants and children compared to adults; therefore A2M is an important inhibitor of thrombin in early life and during childhood.Age-specific differences in thrombin generation as demonstrated by our study possibly play an important role in the thromboprotective mechanism functioning in infants and children. Disclosures:No relevant conflicts of interest to declare.

Thrombin generation in children with sickle cell disease: relationship with age, hemolysis, transcranial doppler velocity, and hydroxyurea treatment

Increased thrombin generation (TG) was described in sickle cell disease (SCD) children. The aim of this study was to characterize TG at the individual level and assess its relationship with age, hemolysis, transcranial Doppler velocity (TCD), and hydroxyurea treatment. TG was triggered in the platelet-poor plasma using tissue factor and phospholipids with addition of thrombomodulin in 97 SCD at steady state and 80 control children. Patients and controls were aged from 2 to 20years, and they were distributed in four categories of age: [2-5], [6-10], [11-15], and [16-20] years. For each subject, ratio of endogenous thrombin potential (rETP) and peak height (rPeak) was calculated as subject's value divided by the mean value of controls of the same age range. rETP and rPeak of patients were considered abnormal when > mean+2SD of controls. LDH, total hemoglobin, and reticulocyte count were measured as markers of hemolysis. Data on hydroxyurea treatment and TCD were collected from medical records. Overall, 38.1% and 44.3% of patients showed elevated rETP and rPeak, respectively. rETP and rPeak decreased significantly with increasing age. In homozygous (SS) patients, TCD velocities and all markers of hemolysis correlated significantly with both rETp and rPeak. Negative correlations were observed between these ratios and the duration of hydroxyurea treatment. Elevated TG in SCD children is mainly related to younger age and to the intensity of hemolysis. There probably a link between TG and cerebral vasculopathy in these patients. Hydroxyurea may have a beneficial effect, which could be related to the duration of treatment.

Profile of thrombin generation in children with acute lymphoblastic leukemia treated by Berlin–Frankfurt–Münster (BFM) protocols

Treatment with L-asparaginase is associated with coagulation disturbances with deep venous thrombosis being the most common clinical consequence. Use of the calibrated automated thrombogram allows precise estimation of thrombin generated in vitro. We show the first data on thrombin generation, measured by calibrated automated thrombography (CAT), in children with acute lymphoblastic leukemia treated with L-asparaginase. Thrombin generation was measured by means of CAT in 23 children treated for acute lymphoblastic leukemia. Samples were obtained at predefined time points during the induction and reinduction phase of acute lymphoblastic leukemia-intercontinental Berlin-Frankfurt-Münster (BFM) 2000 or Associazione Italiana Ematologica Oncologia Pedaitrica Interim BFM 2000 protocols. Antihrombin and fibrinogen were measured on the same sample. Twenty-eight sets of thrombin generation measurements were collected from 23 patients. We observed no significant effect of antithrombin deficiency and/or hypofibrinogenemia on thrombin generation. Endogenous thrombin generation and peak thrombin were significantly higher during induction than in the reinduction phase (P < 0.001). Four patients with severe infection experienced an increase in thrombin generation, reaching maximum in a median of 7.5 days after the onset of infection. Two of those patients developed deep venous thrombosis at the time of peaked endogenous thrombin generation. Thrombin generation in children with acute lymphoblastic leukemia treated according to BFM protocols is significantly higher during the induction phase compared with reinduction and is not substantially affected by hypofibrinogenemia and/or antithrombin deficiency. Severe infection during the induction phase enhances thrombin generation with subsequent risk of thrombosis.

The effect of unfractionated heparin on the haemostatic system of children admitted to a tertiary healthcare setting

Previous studies investigating unfractionated heparin (UFH) therapy have reported age-related differences in UFH response in children as measured by APTT and anti-Xa assay. This study aimed to investigate the effect of UFH on tissue factor pathway inhibitor (TFPI) and thrombin generation and compare these measures to currently used monitoring methods of UFH in paediatric healthcare (APTT; anti-Xa). Venous blood samples were collected from children <16 years (<i>n</i>=17) receiving continuous UFH (14–30U/kg/hr). APTT, anti-Xa, free TFPI, endogenous thrombin potential (ETP) and ETP following inhibition of TFPI (ETP-TFPI) were performed on all samples. Results were analysed as a cohort and agreement between the assays was determined using Pearson's correlation coefficient (r²). The results demonstrate that the contribution of TFPI to the UFH-mediated inhibition of thrombin generation in children appears to be dose-dependent. The correlation of ETP with APTT (r²=70.528) and anti-Xa assay (r²=70.838) was increased compared to the correlation of free TFPI with the APTT (r²=0.328) and anti-Xa assay (r²=0.225), as expected. Potential influences affecting UFH response in children include age of the patient and concentration of UFH in plasma. This pilot study will be used to guide further investigations into the contribution of TFPI to the activity of UFH in children.

Thrombin Generation in Children with Acute Lymphoblastic Leukemia (ALL): Effects of ALL Immunophenotypic Subgroups on Inherited Thrombotic Risk Factors

Thrombin Generation in Children with Acute Lymphoblastic Leukemia (ALL): Effects of ALL Immunophenotypic Subgroups on Inherited Thrombotic Risk Factors

Increased endogenous thrombin generation in children with acute lymphoblastic leukemia: risk of thrombotic complications in L'Asparaginase-induced antithrombin III deficiency

Pediatric patients with acute lymphoblastic leukemia (ALL) are at an increased risk of thromboembolic events. Potential responsible mechanisms include the disease process itself, treatment with chemotherapeutic agents (particularly L-Asparaginase [ASP]), or a combination of the disease and treatment. We studied thrombin regulation in 26 consecutive children with ALL and 14 healthy age- matched controls by: (1) plasma concentrations of prothrombin; (2) plasma inhibition of 125I-alpha-thrombin; and (3) four biochemical markers of in vivo thrombin activation (thrombin complexed to its inhibitor antithrombin III [ATIII; TAT], prothrombin fragment 1.2 (F1.2), activated protein C complexed to the inhibitors alpha 1 antitrypsin [APCAT]), and protein C inhibitor (APC-PCI). Measurements were made at presentation before treatment, after treatment with ASP alone, and during combination chemotherapy with and without ASP. At presentation, the capacity to generate thrombin (reflected by plasma prothrombin concentrations) and the capacity to inhibit thrombin (125I- alpha-thrombin--inhibitor complex formation) were similar in children with ALL compared with that for healthy children. After ASP alone or as part of combination chemotherapy, prothrombin levels were preserved, whereas plasma inhibition of 125I-alpha-thrombin decreased significantly because of a decrease in plasma concentrations of inhibitors, most importantly ATIII. After combination chemotherapy without ASP, plasma concentrations of ATIII and the capacity to inhibit 125I-alpha-thrombin returned to normal values, whereas prothrombin levels increased above control values. Thrombin generation in vivo also differed from healthy controls. At presentation, plasma concentrations of three of four markers of in vivo thrombin activity (TAT, F1.2, APCAT, but not APC-PCI) were increased in children with ALL. Neither ASP alone nor combination chemotherapy with or without ASP significantly altered values of these three markers. In summary, although the in vitro capacity to generate thrombin was preserved, the in vitro capacity to inhibit 125I-alpha-thrombin decreased after ASP therapy. Evidence for increased endogenous thrombin generation was documented in children with ALL at presentation and throughout treatment. We speculate that poor regulation of this thrombin may contribute to thrombotic complications in children with ALL.

Increased Endogenous Thrombin Generation in Children With Acute Lymphoblastic Leukemia: Risk of Thrombotic Complications in L’Asparaginase-Induced Antithrombin III Deficiency

Pediatric patients with acute lymphoblastic leukemia (ALL) are at an increased risk of thromboembolic events. Potential responsible mechanisms include the disease process itself, treatment with chemotherapeutic agents (particularly L-Asparaginase [ASP]), or a combination of the disease and treatment. We studied thrombin regulation in 26 consecutive children with ALL and 14 healthy age-matched controls by: (1) plasma concentrations of prothrombin; (2) plasma inhibition of 125I-alpha-thrombin; and (3) four biochemical markers of in vivo thrombin activation (thrombin complexed to its inhibitor antithrombin III [ATIII; TAT], prothrombin fragment 1.2 (F1.2), activated protein C complexed to the inhibitors alpha 1 antitrypsin [APCAT]), and protein C inhibitor (APC-PCI). Measurements were made at presentation before treatment, after treatment with ASP alone, and during combination chemotherapy with and without ASP. At presentation, the capacity to generate thrombin (reflected by plasma prothrombin concentrations) and the capacity to inhibit thrombin (125I-alpha-thrombin--inhibitor complex formation) were similar in children with ALL compared with that for healthy children. After ASP alone or as part of combination chemotherapy, prothrombin levels were preserved, whereas plasma inhibition of 125I-alpha-thrombin decreased significantly because of a decrease in plasma concentrations of inhibitors, most importantly ATIII. After combination chemotherapy without ASP, plasma concentrations of ATIII and the capacity to inhibit 125I-alpha-thrombin returned to normal values, whereas prothrombin levels increased above control values. Thrombin generation in vivo also differed from healthy controls. At presentation, plasma concentrations of three of four markers of in vivo thrombin activity (TAT, F1.2, APCAT, but not APC-PCI) were increased in children with ALL. Neither ASP alone nor combination chemotherapy with or without ASP significantly altered values of these three markers. In summary, although the in vitro capacity to generate thrombin was preserved, the in vitro capacity to inhibit 125I-alpha-thrombin decreased after ASP therapy. Evidence for increased endogenous thrombin generation was documented in children with ALL at presentation and throughout treatment. We speculate that poor regulation of this thrombin may contribute to thrombotic complications in children with ALL.