Objective: To determine the frequency of different causes of inherited thrombophilia and evaluate clinical presentations in patients presenting with documented venous or arterial thrombosis. Study Design: Cross-sectional study. Place and Duration of Study: Armed Forces Institute of Pathology Rawalpindi, Pakistan from Jan to Jun 2022. Methodology: One hundred and seven patients who fulfilled the selection criteria and gave informed consent in written form were enrolled. Clinical presentations were noted down and patients were assessed for inherited thrombophilia. Polymerase chain reaction was used for the detection of factor V Leiden mutation and prothrombin gene mutation. Pro C global clotting based screening test was used to determine the anticoagulatory capacity of protein C and S. Quantitative determination of the functional activity of antithrombin was performed on CS5100 automated coagulation analyzer. Results: The mean age of the patients was 29.31±14.17 years. Inherited thrombophilia was present in 26(24.3%) patients. Factor V Leiden mutation was present in 14(53.8%), antithrombin deficiency in 6(23.1%), protein C deficiency in 3(11.5%), protein S deficiency in 2(7.7%) and prothrombin gene mutation in 1(3.9%) patient. Commonest clinical presentation was deep venous thrombosis in 10(38.5%) patients followed by pulmonary embolism in 5(19.2%), portal vein thrombosis in 3(11.5%), superficial venous thrombosis in 3(11.5%). Conclusion: The commonest inherited cause of thrombophilia was factor V Leiden mutation and the commonest presenting complaint was deep venous thrombosis.

The objective of the study is to critically review the literature about clinical evidence on the efficacy and safety of fitusiran among patients with hemophilia A or B. A targeted search of PubMed, Embase, the Cochrane Library, and ClinicalTrials.gov was performed from inception through November 2025 using the terms fitusiran, antithrombin, RNA interference, siRNA, and hemophilia A or B. Eligible studies were randomized controlled trials across all phases enrolling patients with hemophilia A or B. The review incorporated 2 phase 1 studies, 1 phase 2 study, and 4 phase 3 trials. Fitusiran prophylaxis reduced annualized bleeding rates by about 70% to 90% compared with on-demand therapy or previous prophylaxis using bypassing agents, and by up to 50% compared with prior prophylaxis with clotting factor concentrates. Between 50% and 65% of participants experienced no bleeds requiring treatment. Health-related quality of life improved, with mean reductions in Hemophilia-specific Quality of Life Questionnaire for Adults (Haem-A-QoL) scores ranging from -4.6 to -12.3. Safety evaluations showed aminotransferase elevations in 19% to 25%, gallbladder events in 13% to 15%, and thrombotic events in ≤5% of patients, primarily associated with low antithrombin levels or excessive factor use. Long-term extension studies confirmed sustained bleed protection and safety with antithrombin-guided dosing.Relevance to patient care and clinical practice in comparison to existing drugs:Fitusiran is a subcutaneous nonfactor prophylactic treatment that lowers antithrombin to rebalance coagulation with or without inhibitors in patients with hemophilia A and B. It is administered every 2 months, and associated with fewer bleeds, and improved quality of life compared with standard of care. Fitusiran expands prophylactic options for hemophilia A and B, providing sustained bleed protection with infrequent dosing. Integration into practice requires monitoring of antithrombin activity to mitigate thrombotic or bleeding risk, and liver and gallbladder functions for safety.

Superiority of a combined antithrombin and activated protein C model for predicting coagulopathy and mortality in pneumonia-related sepsis: A prospective cohort study.

This study aimed to determine coagulation changes in bitches with pyometra based on a series of coagulation tests and thromboelastography (TEG), and to assess the incidence of disseminated intravascular coagulation (DIC). Eighteen bitches with pyometra and thirty-four control bitches were examined. Haematological, biochemical, and following haemostasis parameters were measured, including: prothrombin time (PT), activated partial thromboplastin time (aPTT), antithrombin activity (AT), and levels of fibrinogen (FBG), d-dimers (DD), tissue factor (TF), plasminogen (PLG), tissue plasminogen activator inhibitor 1 (TPAI-1), and thromboelastography. DIC was considered present if three or more of these parameters were abnormal: platelet count (<153 × 109/l), PT (>8.1 s), aPTT (>25.5 s), FBG (<0.6 g/l), DD (>0.2 mg/l), and AT (<107%). Significant differences were found in the PT, aPTT, FBG, DD, TPAI-1, clotting time, α-angle, and maximal amplitude. According to our scoring system, two patients were DIC positive. The study found alterations in several coagulation tests and hypercoagulable TEG tracings in bitches with pyometra, which point to excessive activation of coagulation, delayed fibrinolysis, and the presence of DIC. No patient bled abnormally, which may suggest that DIC is not overt in the majority of pyometra patients.

BackgroundHereditary antithrombin deficiency (HATD) is a rare disease caused by mutations in the SERPINC1 gene characterized with venous thromboembolism and/or arterial thrombotic events. We identified a proband with recurrent arterial and venous thrombosis at multiple anatomical sites and subsequently performed comprehensive thrombophilia screening and genetic analysis within the kindred.MethodsMutation screening of the SERPINC1 gene in the proband and family members was conducted using Sanger sequencing. Wild-type and mutant (c.473T > A; p.Leu158Gln) SERPINC1 expression plasmids were constructed and transiently transfected into HEK293T cells. Functional consequences of the variant were assessed through immunoblotting, immunofluorescence, enzyme-linked immunosorbent assay (ELISA), and computational structural analysis.ResultsThrombophilia evaluation revealed significantly reduced antithrombin activity (46.2%) in the proband. Sanger sequencing identified an unreported heterozygous missense variant (c.473T > A; p.Leu158Gln) in SERPINC1. Cellular studies demonstrated that this mutation reduced both the quantity and functional activity of secreted antithrombin. Immunoblot analysis indicated a slightly faster migration of the mutant protein compared to wild-type, while immunofluorescence revealed abnormal cytoplasmic aggregation. Bioinformatics analysis confirmed substitution of leucine-158 by glutamine without disruption of conserved disulfide bonds (Cys40-Cys160, Cys128-Cys182, Cys247-Cys430) or N-glycosylation sites (Asn128, Asn167, Asn187, Asn224).ConclusionWe establish the c.473T > A (p.Leu158Gln) variant in SERPINC1 as a pathogenic mutation underlying type I HATD, characterized by impaired secretion, cytoplasmic retention, and reduced functional activity of the mutant protein.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12959-025-00801-0.

Biomarkers for venous thromboembolism in children with central venous catheters

Background and Aims: Fitusiran is an RNA interference therapy that lowers antithrombin (AT) levels, thereby restoring hemostatic balance in patients with hemophilia A or B, regardless of inhibitor status. However, clinical experience with perioperative management of major surgery in patients receiving fitusiran is still limited. We report three major surgical procedures performed in two patients with severe hemophilia A without inhibitors, treated with fitusiran, focusing on coagulation parameters and clinical outcomes. Methods: Two adult patients with severe hemophilia A without inhibitors, enrolled in the ATLAS-OLE trial and receiving monthly prophylaxis with subcutaneous fitusiran dat a dosage of 80 mg or 20 mg every 2 months as part of an investigational therapy, underwent the following major surgical procedures: (1) Patient 1 underwent a robot-assisted sigmoidectomy with colorectal anastomosis using the Knight-Griffen technique for the treatment of sigmoid adenocarcinoma; (2) Patient 2 underwent total right knee arthroplasty, followed by (3) joint revision, arthrolysis, and patellar resurfacing. We decided not to discontinue Fitusiran treatment prior to surgery, and also chose not to administer antithrombin to normalize antithrombin levels. Perioperative prophylaxis was conducted using low-dose FVIII, 10 IU/kg/day. Perioperative monitoring included antithrombin (AT, %), hemoglobin (Hb), prothrombin time (PT), activated partial thromboplastin time (aPTT), and factor VIII (FVIII) levels. Results: The three major surgeries (two orthopedic and one abdominal) in patients with hemophilia A without inhibitors, with a mean age of 50.7 years (±17.7 years), receiving prophylaxis with fitusiran, were completed without perioperative complications. The last administration of fitusiran occurred 15, 56, and 77 days before the surgery and the antithrombin (AT) activity level on the day of surgery were 14%, 23.1%, and 21.5%, respectively. A total dose of FVIII (Beriate) ranging from 65 to 90 IU/kg was administered throughout the hospitalization. The median FVIII levels during hospitalization were 27.4%, 13.6%, and 13.4%. Hemoglobin (Hb) values showed a mild/moderate decrease at discharge, with reductions of 0.6 g/L, 0.7 g/L, and 2.1 g/L in the three cases, without signs of active bleeding (Tab 1). Excellent hemostatic control was achieved in all surgeries, with minimal blood loss, and no patient required transfusions or showed signs of significant anemia. No antithrombotic prophylaxis was administered, and no clinical signs of thrombosis were observed during the entire course of treatment. The administration times of fitusiran were maintained according to protocol in the postoperative period. Conclusions: In patients with severe hemophilia A without inhibitors undergoing fitusiran prophylaxis, major surgeries can be safely and effectively performed using low daily doses of FVIII. The use of fitusiran in this context has demonstrated its ability to provide adequate hemostasis throughout the perioperative period. It is important to emphasize that the absence of bleeding complications, the lack of significant anemia, and the absence of thrombotic events during the perioperative course further highlight the safety of this therapeutic strategy.

BackgroundTo identify early diagnostic biomarkers for sepsis-induced disseminated intravascular coagulation, we investigated the relationship between the novel coagulation biomarkers and antithrombin with the development of Disseminated intravascular coagulation post-admission, as well as the prognosis of patients with sepsis.MethodsWe retrospectively collected data from septic patients admitted to the Emergency Intensive Care Unit (EICU) of a teaching hospital between October 2021 and September 2023. Multivariate logistic regression analysis was performed to identify risk factors, and receiver operating characteristic (ROC) curve analysis was used to assess the performance of the predictive model. In addition, non-parametric bootstrap analysis with 1,000 replications was conducted to evaluate the internal stability and empirical power of the predictive models, particularly given the limited sample size.ResultsAmong 91 septic patients, 15 were diagnosed with DIC. Soluble thrombomodulin (OR: 1.28, 95% CI: 1.033–1.586, P = 0.024) and antithrombin activity (OR: 0.887, 95% CI: 0.792–0.994, P = 0.039) were identified as independent risk factors for the development of DIC in septic patients. The area under the curve (AUC) for soluble thrombomodulin and antithrombin was 0.788 and 0.757, respectively. When combined, the AUC increased to 0.858. Prothrombin Time (HR: 1.058, 95% CI: 1.016–1.102, P = 0.007) and APACHE II score (HR: 1.071, 95% CI: 1.005–1.141, P = 0.035) were identified as independent risk factors for 28-day mortality in septic patients. When combined, the AUC increased to 0.834. Bootstrap validation demonstrated strong discriminatory performance of both models, with a mean bootstrap AUC of 0.865 (empirical power = 0.994) for the DIC prediction model, and 0.836 (empirical power = 0.996) for the 28-day mortality model, further supporting the robustness and reliability of the findings despite the small sample size.ConclusionElevated soluble thrombomodulin and decreased antithrombin may be associated with the early onset of disseminated intravascular coagulation in sepsis, but showed limited predictive value for 28-day mortality.

BackgroundAntithrombin, a key regulator of the coagulation cascade, is often decreased in patients with sepsis-associated disseminated intravascular coagulation (DIC). Antithrombin is commonly supplemented when activity levels fall to 70% or below in Japan. While there is considerable interindividual variability in antithrombin activity following treatment, the factors contributing to this variability remain unclear. This study aims to identify the determinants of post-treatment antithrombin activity levels and to investigate the potential association between antithrombin activity and bleeding risk.MethodsWe conducted a retrospective analysis using data from the post-marketing surveillance of antithrombin concentrate in patients with sepsis-associated DIC. Changes in antithrombin activity were calculated as: (Day 1 activity − baseline activity [%]) divided by the daily dose (international units [IU] per kilogram of body weight). Logistic regression analysis was employed to identify factors associated with changes in antithrombin activity following supplementation and factors related to bleeding risk. Additionally, Kaplan–Meier survival curves were used to examine the relationship between antithrombin activity and 28-day survival outcomes.ResultsA total of 1,524 patients were included in the analysis. The median baseline antithrombin activity was 49%, which increased to 74% on day 1 post-treatment. The mean change in antithrombin activity was 0.99% /IU/kg and followed a normal distribution. The SOFA score ≥ 13 (p = 0.035) and FDP score ≥ 3 (≥ 25μg/mL), part of the JAAM DIC score, (p = 0.016) were significantly associated with lower antithrombin activity increase. Patients achieving ≥ 1% /IU/kg increase showed a higher 28-day survival rate (relative risk: 0.72, p = 0.004). No significant association was found between antithrombin doses or activity changes and bleeding risk.ConclusionA higher SOFA score and FDP level were associated with a smaller increase in post-treatment antithrombin activity. There was no clear association between antithrombin doses and bleeding risk. The present study suggests the necessity of individualized dosing beyond weight-based regimens.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12959-025-00779-9.

Abstract Background The increasing consolidation of pathology laboratories into central hubs, while enhancing efficiency, often leads to extended turnaround times. Drone delivery can offer a faster, more sustainable alternative for traditional ground transport to mitigate this. Using a multi-faceted approach, we rigorously validated drone delivery as a viable inter-hospital logistics solution, ensuring sample quality was not negatively impacted. Methods The validation process was structured in three distinct phases: drone operator technical validation, temperature validation of simulated samples and scientific validation of pathology samples. Each phase required approval from key laboratory and clinical stakeholders before drone delivery was approved for routine clinical service. This abstract focuses on the scientific validation of pathology samples, employing a tailored approach to the available instrumentation and testing repertoire at each site. Three different primary methodologies were used across the three departments involved: Specialist Haemostasis: Tests were only available at the receiving laboratory. Therefore, all sample tubes were split at the sending laboratory, with one aliquot transported by drone and the other by ground courier to the receiving laboratory. Tests included: (1) vWf:GP1bR assay, (2) Factor VIII (baseline), (3) Factor IX (baseline), (4) Antithrombin activity IIa, (5) Antithrombin activity Xa, and (6) Protein C activity. Biochemistry: For tests available at the sending laboratory, samples were first analysed on site before an aliquot was drawn for drone transport to the receiving laboratory. Tests included: (1) Potassium, (2) Lactate dehydrogenase, (3) Bicarbonate, (4) Total bilirubin and, (5) Phosphate. For tests available only at the receiving laboratory, samples were split as for Specialist Haemostasis. Tests included: (1) Cortisol and (2) Lactate. Special Haematology: Samples were first analysed on site at the sending laboratory before being split, with one aliquot transported by drone and another by ground courier to the receiving laboratory. Tests included: (1) CD3, (2) CD4, (3) CD8, (4) CD19 and, (5) CD16/56. Validation criteria were predefined by the relevant laboratory department and data were compared using a combination of analyser uncertainties, inter-analyser variation, and statistical analyses. For statistical comparison, Wilcoxon signed-rank tests or students paired t-tests were used depending on data normality (assessed using Shapiro-Wilk). Results All tested pathology sample types passed validation criteria, with no significant difference between in-house-tested, drone-delivered, and ground-transported samples. Throughout all flights, the temperature within the thermal canister used for packing the samples was monitored to ensure sample stability, remaining consistent despite fluctuating weather conditions. Drone delivery achieved an average flight time of approximately 2 minutes, significantly faster than the 35-minute average ground transport route, a 94% reduction in transit time. Conclusion Following successful validation, an on-demand drone delivery service was launched in October 2024 between Guy*s Hospital and St Thomas* Hospitals in London and continues to operate. To date, over two thousand samples have been transported via nearly 300 flights, leading to faster analysis times and mitigating logistical challenges associated with scheduled ground transport. Future plans include expanding the range of validated tests, establishing new flight routes to other regional hospitals, and demonstrating improvements to patient care and laboratory efficiency.

This study systematically compared the genetic characteristics and functional activities of hirudins and their encoding genes between Hirudo nipponia (Hnip1-3) and Hirudo tianjinensis (Htia1-3) through bioinformatics analysis, recombinant protein eukaryotic expression, and activity assays. The results revealed 42 nucleotide variation sites and 27 amino acid variation sites across both species. All six genes were expressed and significant pairwise differences between genes were detected within each species. All hirudins were identified as secretory proteins, with Hnip2, Hnip3, and Htia1 showing higher docking scores with thrombin. Four recombinant proteins (Hnip1, Hnip2, Htia1, and Htia2) exhibited antithrombin activity, with Hnip1 displaying the strongest activity. No significant differences were observed in the sequence variation, gene expression, physicochemical properties, predicted three-dimensional structures, or antithrombin activity of hirudins between the two leech species. This may stem from substantial heterogeneity in the genetic makeup and functional characteristics of distinct hirudins within each species, ultimately reducing the statistical power of these interspecific comparisons. Integrating gene expression profiles with recombinant protein activity assessments revealed that H. nipponia hirudins exhibit superior antithrombotic potency compared to those of H. tianjinensis. This study establishes a theoretical foundation for medicinal leech resource development and provides critical data for innovative antithrombotic drug discovery.

To evaluate whether plasma levels of placental extracellular vesicles (pcEVs), the EV-scavenging factor lactadherin, and prothrombotic markers predict fetal growth restriction (FGR) and/or fetal distress (FD) in established severe pre-eclampsia (sPE). We recruited 80 sPE patients, 41 normal pregnancies, and 27 non-pregnant women. SPE patients were further dichotomized into event and non-event groups based on the occurrence of FGR/FD during a follow-up period of 77 days. Plasma levels of pcEVs, lactadherin, von Willebrand factor (VWF), antithrombin (AT), and tissue plasminogen activator-plasminogen activator inhibitor complex (tPAI-C) were analyzed for predicting FGR and FD. Plasma levels of pcEVs, lactadherin, VWF, and tPAI-C were progressively increased from non-pregnant women, women with normal pregnancies, and patients with sPE, whereas levels of AT were decreased. Subgroup analyses further showed that pcEVs, lactadherin, and tPAI-C were 2.7, 1.5, and 1.5 times higher in sPE patients with FGR/FD than those without FGR/FD. In contrast, levels of AT were decreased by 10%. The receiver operating characteristic (ROC) analysis found pcEVs to be 84.4% sensitive and 71.4% specific for predicting FGR/FD. Logistic regression analysis indicated that levels of pcEVs were associated with heavy proteinuria (OR = 4.657) and combined antihypertensive therapy (OR = 6.972) in sPE patients. Patients with pcEVs exceeding 6524/μL had an elevated cumulative risk of FGR/FD (log-rank χ2 = 25.964, P = 0.000) and predicted FGR/FD in sPE patients, with a hazard ratio of 6.940. Plasma pcEVs may serve as an independent predictive biomarker for FGR/FD in sPE patients.

Current antithrombotic therapies face dual constraints of bleeding complications and monitoring requirements. Although natural hirudin provides targeted thrombin inhibition, its clinical adoption is hindered by sourcing limitations. This study developed a recombinant hirudin variant HMg (rHMg) with enhanced anticoagulant activity through genetic engineering and established cost-effective large-scale production methods. The synthesised HMg gene was expressed in E. coli BL21 via a pET vector plasmid, followed by nickel-affinity purification. Systematic evaluations demonstrated rHMg’s antithrombin activity of 9573 ATU/mg, dose-dependent prolongation of APTT/PT/TT. It has superior thrombin inhibition with the IC50 and Ki values were 2.8 and 0.323 nM respectively compared to FDA approved drug bivalirudin (p < 0.001). The high-yield prokaryotic expression of rHMg with enhanced anticoagulant efficacy provides a novel strategy for developing affordable antithrombotic drugs, showing significant potential for cardiovascular disease management.

Genotype vs laboratory phenotype correlation of defects in natural anticoagulants in patients with venous thromboembolism.

Analysis of Risk Factors for Heparin Resistance During Cardiac Surgery: Does Antithrombin Deficiency Cause Heparin Resistance?

Identify alterations in biochemical and haemostatic variables between tumour-bearing dogs with and without metastasis that can be used to predict the presence of metastasis. Thirty dogs with sarcoma and 29 with carcinoma were included in the analysis. Serum biochemistry profiles and haemostatic variables (haematocrit value, platelet count, thromboelastography (TEG), fibrinogen, Factor X, VII, antithrombin activity and D-dimer concentration) were measured for all dogs. All dogs underwent complete post-mortem and histopathological evaluations. For tumour-bearing dogs without intracavitary haemorrhage, measured variables were compared between dogs with and without metastasis, and univariate and multivariable analysis were performed to identify predictors of metastasis. Metastasis was identified in 31 of 59 (53%) dogs, of which 5 of 31 (16%) had metastasis to the regional lymph node only and 26 of 31 (84%) had distant metastasis. Sodium, ionised calcium, TEGlysis % at 30 and 60 minutes (Ly60) were significantly lower in tumour-bearing dogs without intracavitary haemorrhage with metastasis compared to dogs without metastasis. Multivariable analysis identified sodium <142.5 mmol/L as 64% sensitive (CI95%:45% to 82%) and 63% specific (CI95%:44% to 81%); and Ly60 < 1.0% as 68% sensitive (CI95%: 49% to 88%) and 78% specific (CI95%:61% to 95%) for prediction of the presence of metastasis. Parallel interpretation of lower sodium and decreased Ly60 resulted in high sensitivity (96%) for the presence of metastasis. Sodium and TEG-based decreased fibrinolysis were associated with metastasis in tumour-bearing dogs without haemorrhage; when identified, they should prompt further diagnostics to detect possible metastasis of a primary carcinoma or sarcoma.

BackgroundGestational diabetes mellitus (GDM) has been increasingly associated with heightened cardiovascular and thrombotic risk. This study aimed to evaluate hemostatic and metabolic profiles in women with GDM to explore early markers of vascular dysfunction.MethodsA retrospective cross-sectional study was conducted among 250 pregnant women diagnosed with GDM between December 2022 and October 2023 at multiple tertiary healthcare facilities in Pakistan. Only GDM cases were included; normoglycemic controls were not part of this analysis. Cardiovascular risk was assessed using surrogate markers, including fibrinogen, D-dimer, plasminogen activator inhibitor-1 (PAI-1), and antithrombin, in conjunction with clinical data such as blood pressure, BMI, smoking status, and comorbidities. Threshold values were interpreted relative to gestational-age norms where available. The influence of treatment modalities (insulin, metformin, diet) was explored. Ethical approval was obtained from the institutional review board prior to data access.ResultsWomen with GDM showed elevated levels of fibrinogen (mean: 3.48 g/L), D-dimer (mean: 863 ng/mL), and PAI-1, along with reduced antithrombin activity, suggestive of a prothrombotic state. Comorbidities such as obesity, hypertension, and tobacco use appeared to amplify this risk. No significant differences were found in hemostatic markers across treatment modalities.ConclusionGDM was associated with biochemical evidence of vascular strain and thrombogenicity. These findings highlight the potential value of integrated hemostatic and cardiovascular surveillance during pregnancy. Further studies comparing GDM to normoglycemic pregnancies are warranted to confirm causality and refine risk stratification.

Oral functional protein Z: Mitigation of thrombosis via thrombin inhibition to prevent cardiovascular disease.

Antithrombin (AT) plays a crucial role in the human anticoagulant system and has extensive clinical applications. However, traditional detection methods often require large sample volumes, complex procedures, and lengthy processing times. Methods: We integrated digital microfluidics technology with AT detection to develop a point-of-care testing (POCT) device that is user-friendly and fully automated for real-time AT testing. Results: This device allows for automation and enhanced adaptability to various settings, requiring only a minimal sample volume (whole capillary blood), thereby omitting steps such as plasma separation to save time and improve clinical testing efficiency. Comparisons with conventional AT activity detection methods demonstrate a high degree of consistency in the results obtained with this device. Conclusion: The AT detection system we developed exhibits significant effectiveness and holds substantial research potential, positioning it to evolve into a clinically impactful POCT solution for AT assessment.

Hereditary antithrombin (AT) deficiency is a rare autosomal dominant disorder that predisposes to the development of recurrent venous thromboembolism (VTE). Diagnosis is based on the measurement of reduced AT activity in plasma. However, not all commercial AT activity assays are equally suited for diagnosis since they differ in sensitivity toward different AT mutations.The aim of this study was to compare the ability of commonly used AT activity assays to diagnose inherited antithrombin deficiency, with a focus on type II AT deficiencies. We used samples from genetically confirmed AT deficient subjects (n = 76) and from patients with request for AT activity measurement for diagnostic purposes (n = 152). AT activity was measured with five commercial assays on three analyzers.All reagent/analyzer combinations showed specificities varying from 87 to 100%, except for 1 assay (56.5% specificity). Diagnostic sensitivity varied widely between assays, from 36.8% to 100%. All reagent-analyzer combinations correctly identified variants causing type I AT deficiencies but only one variant responsible for type II heparin binding site (HBS) deficiency: p.Arg79Cys. For one of the assays, we observed a large difference in sensitivity (82.9 versus 55.3%) toward antithrombin type II HBS variants depending on the coagulation analyzer on which it is performed, suggesting that incubation time of sample and substrate could be a crucial driver of the sensitivity toward variants causing type II antithrombin deficiency. Our results suggest that inherited antithrombin deficiency is probably underestimated and improved diagnostic strategies are mandatory.