BACKGROUND AND PURPOSE:Cryptogenic strokes, accounting for 25%-40% of ischemic strokes, represent a major challenge in secondary prevention due to their uncertain etiology and high recurrence risk. Identifying biomarkers to reliably distinguish cardioembolic (CE) strokes among embolic strokes of undetermined source (ESUS) could help guide therapeutic decisions. Previous studies have indicated thrombus DNA content as a potential biomarker of CE stroke etiology, but direct quantification of fibrin, another key component, has not been adequately explored. METHODS:We analyzed thrombi collected from 186 ischemic stroke patients undergoing endovascular treatment between 2019 and 2023. Thrombi were processed using a quantitative method based on ex vivo tPA-mediated fibrinolysis followed by mechanical homogenization. Stroke etiology was classified according to TOAST criteria: 40% cardioembolic, 24% non-cardioembolic (large artery atherosclerosis or dissection), and 36% ESUS. Biomarker content was correlated with stroke etiology, and the diagnostic performance of DNA and fibrin (D-dimer) content was evaluated. RESULTS:Cardioembolic thrombi contained significantly higher levels of DNA (median [IQR]: 325.3 [177-484] ng/mg) and D-dimer (17.5 [9.1-23.8] μg/mg) compared to non-cardioembolic thrombi (DNA: 128 [76.4-263] ng/mg; D-dimer: 11.4 [6.8-13.2] μg/mg), with no significant differences observed in heme or GPVI content. The combined use of thrombus DNA and fibrin (D-dimer) content provided good discrimination between CE and non-CE thrombi, with an area under the ROC curve of 0.79 (95% CI, 0.70-0.87). CONCLUSION:DNA and fibrin content in thrombi are promising biomarkers for identifying cardioembolic stroke etiology. Prospective studies should evaluate their use in selecting ESUS patients who may benefit from anticoagulant therapy.

Abstract: Phase 3 trials evaluating inhibitors of coagulation factor XI (FXI) and/or its activated form (FXIa) as novel anticoagulant drugs are ongoing. These agents include parenteral monoclonal antibody (abelacimab) and oral small molecules (milvexian, asundexian). We investigated the extent to which standard and specialized coagulation assays are affected by FXI(a) inhibitors in a multicenter study involving 23 laboratories. FXI(a) inhibitors were spiked into pooled normal plasma at concentrations covering those observed in phase 2/3 clinical trials: 50 to 2000 ng/mL for milvexian and asundexian, and 1 to 30 μg/mL for abelacimab. Actual plasma concentrations were measured by high-performance liquid chromatography–tandem mass spectrometry. Assays were performed blindly using 5 to 11 different combinations of reagent/analyzer depending on the assay. Prothrombin time, Clauss fibrinogen, and clotting activity of FII, FV, FVII, and FX were not affected in a clinically relevant manner. Activated partial thromboplastin time (aPTT) was prolonged in a concentration-dependent manner, with milvexian having the greatest impact followed by abelacimab and asundexian. Clotting activity of FVIII, FIX, FXI, and FXII was underestimated. Such interference was prevented by high plasma dilution (up to 1:160) before the test, except for abelacimab: FXI clotting activity remained decreased, even at low concentration (2.5 μg/mL). FXI(a) inhibitors did not affect lupus anticoagulant (LA) testing using dilute Russell viper venom time but may lead to false-negative result with LA-sensitive aPTT reagents. Protein C anticoagulant activity was overestimated, whereas no impact on protein S anticoagulant activity was observed. This study provides a comprehensive laboratory framework for interpreting clotting assays in future patients receiving FXI(a) inhibitors.

Immunofluorescence-based platelet phenotyping using peripheral blood smears has recently emerged as a promising method for characterizing a subgroup of inherited platelet disorders (IPD). A single-center study demonstrated its potential for accurate diagnosis of 9 disorders with characteristic platelet structural changes. The aim of this study was to evaluate the reproducibility of this approach through an interlaboratory validation study. Native, air-dried blood smears from healthy controls and patients with confirmed IPD were shipped to 7 participating laboratories, blinded for the sample origin. Samples were fixed and stained using a shared panel of 13 commercially available primary antibodies and 2 fluorescence-labelled secondary antibodies. Laboratories formulated diagnostic predictions based solely on immunofluorescence findings. The pre-workshop method establishment involved other samples and feedback with the coordinating laboratory to address technical issues before blinded sample validation. All 7 laboratories (Brisbane, Greifswald, Murcia, Paris, Pavia, Perugia, and Tübingen) correctly diagnosed MYH9-related disease, Bernard-Soulier syndrome, Glanzmann thrombasthenia, and GFI1B-related thrombocytopenia. Six of 7 laboratories accurately identified TUBB1-related disorder and quantitative δ-storage pool disorder, while 5 of 7 correctly diagnosed GATA1-related thrombocytopenia. Immunofluorescence-based platelet phenotyping on peripheral blood smears demonstrated high sensitivity for diagnosing MYH9-related disease, Bernard-Soulier syndrome, Glanzmann thrombasthenia, and GFI1B-related thrombocytopenia, and reasonable sensitivity for TUBB1-related disorder, quantitative δ-storage pool disorder, and GATA1-related thrombocytopenia. Immunofluorescence analysis of blood smears may be of help in the diagnostic work-up of IPD.

Background:Acute ischemic stroke (AIS) is a significant complication of cancer and may reveal occult malignancy. Whether cancer-related AIS (CAS) provides specific biological features remains unclear. Objectives:This case-control study aimed to characterize thrombi and plasmas from patients with CAS. Methods:Nine consecutive patients with CAS, including 3 nonbacterial thrombotic endocarditis (NBTE), and age- and sex-matched AIS controls with cardioembolism (CE, n = 16) or large artery atherosclerosis (LAA, n = 16) were included from the compoCLOT study. Thrombi retrieved after endovascular thrombectomy underwent ex vivo thrombolysis using recombinant tissue-type plasminogen activator and were analyzed for composition. Plasma biomarkers were also assessed. Results:CAS thrombi were resistant to tissue-type plasminogen activator lysis compared with LAA thrombi (median thrombus weight conservation, 92% vs 9%; P = .0002) and, to a lesser extent, compared with CE thrombi (92% vs 43%; P = .06). Thrombolysis resistance correlated negatively with red blood cell content (P < .0001) but positively with platelet factor-4 (P = .0014), von Willebrand factor (P = .0002) and DNA content (P < .0001). A subgroup of macroscopically white thrombi (n = 6), characterized by low red blood cell and high von Willebrand factor content, was identified in CAS, encompassing all 3 NBTE cases. Plasma D-dimer, fibrin monomers, extracellular vesicle-associated tissue factor and myeloperoxidase were significantly higher in patients with CAS than in the combined LAA and CE control groups (31,290 vs 1900 µg/L; 143 vs 9 μg/mL; 143 vs 9 fM; and 51 vs 25 ng/mL, respectively). Conclusions:CAS thrombi exhibit distinct properties, with white thrombi as a hallmark of undiagnosed NBTE. Furthermore, plasma biomarkers such as D-dimer, fibrin monomers, extracellular vesicle-associated tissue factor and myeloperoxidase could help in cancer screening in AIS of unknown etiology.

Background: The increased interest in anti-platelet factor 4 (PF4)-heparin complex (anti-PF4/H) antibodies following the COVID-19 pandemic has established them as crucial players in immunothrombosis. Objectives: We aimed to investigate the involvement of anti-PF4/H antibodies during COVID-19 and after vaccination, particularly in patients with systemic inflammatory disease (SID). Methods: This retrospective study analyzed the presence of anti-PF4/H antibodies and their ability to induce platelet activation in COVID-19 patients with and without suspected heparin-induced thrombocytopenia (HIT), vaccine-induced immune thrombotic thrombocytopenia (VITT) patients, and in controls and SID patients following COVID-19 vaccination. Results: No significant increase in anti-PF4/H antibody levels was observed during COVID-19 regardless of disease severity. Despite a 2-fold increase in HIT suspicion observed during the pandemic, there was no corresponding increase in HIT diagnoses. Additionally, no significant increase in anti-PF4/H levels was noted after vaccination, even in SID patients. None of the positive anti-PF4/H antibodies detected in COVID-19 or vaccination cohorts induced platelet activation, measured by soluble P-selectin levels and flow cytometry-based on platelet microvesicle generation. Finally, in VITT patients, unlike in HIT patients, anti-PF4/H levels were strongly associated with platelet microvesicle assay and moderately with soluble P-selectin levels. Conclusion: Our study found no significant increase in anti-PF4/H antibodies in COVID-19 or after vaccination, including in SID patients. However, in VITT patients, but not in HIT patients, these antibodies were correlated with platelet activation. This finding suggests that anti-PF4/H antibodies play a different role in the pathophysiology of VITT but that their interest is limited outside clear contexts of HIT/ VITT suspicion.

ABSTRACT The concentration of cells is a key component of modern blood tests. Given the biomarker potential of extracellular vesicles (EVs) in blood, we aimed to establish reference ranges for blood cell‐derived EVs using flow cytometry. To address the orders‐of‐magnitude variability in reported EV concentrations between different flow cytometers (FCMs), we first validated a calibration methodology to enable reproducible EV concentration measurements. The methodology was evaluated in an interlaboratory comparison study and shows that calibration reduces the median absolute deviation of EV concentrations measured on 25 different FCMs from 67 % to 25 %–31 %. The calibration methodology was then used to determine reference ranges of erythrocyte‐, leukocyte‐, and platelet‐derived EVs in human blood plasma in a cohort of healthy individuals (n = 224). This study demonstrates that calibration enables comparable concentration measurements of blood cell‐derived EVs, thereby bringing EVs one step closer to clinical applications.

BACKGROUND:Hemorrhagic transformation (HT) frequently occurs in acute ischemic stroke patients with a large vessel occlusion undergoing endovascular therapy (EVT), significantly impacting functional outcomes. We aimed to determine whether an early fibrinogen depletion coagulopathy (FDC) was associated with HT following bridging therapy (ie, intravenous thrombolysis [IVT] followed by EVT), and to identify its associated factors. METHODS:We retrospectively analyzed prospectively collected data from 296 patients with acute ischemic stroke with a large vessel occlusion who underwent EVT alone or bridging therapy, with fibrinogen levels measured both before baseline imaging and at the start of the EVT procedure. FDC was defined as a fibrinogen level <2.0 g/L at the start of the EVT procedure, with an absolute decrease >1.0 g/L from baseline. The primary outcome was the occurrence of any HT at 24 to 36 hours. Secondary outcomes included symptomatic HT, parenchymal hematomas, and 3-month mortality. The relationships between FDC and outcomes were studied using multivariable logistic regression analyses, adjusting for relevant confounders. We also studied baseline characteristics associated with FDC occurrence. RESULTS:Of the 296 patients enrolled, 102 (34.5%) experienced HT, and 54 (18.2%) developed FDC. FDC was strongly associated with IVT use (53/161 [32.9%] versus 1/135 [0.7%] in IVT-treated and non-IVT-treated patients, respectively; P<0.01). In patients receiving bridging therapy, FDC occurrence was independently associated with any HT (adjusted odds ratio, 2.33 [95% CI, 1.11-4.91]), symptomatic HT (adjusted odds ratio, 3.35 [95% CI, 1.20-9.40]), parenchymal hematomas (adjusted odds ratio, 2.87 [95% CI, 1.14-7.24]), and 3-month mortality (adjusted odds ratio, 3.82 [95% CI, 1.47-9.93]). None of the 26 patients who received tenecteplase experienced FDC, compared with 53 of 135 (39.3%) patients treated with alteplase (P<0.01). CONCLUSIONS:Following bridging therapy, FDC is a frequent event associated with increased risks of any HT, symptomatic HT, parenchymal hematomas, and 3-month mortality. FDC did not occur following IVT with tenecteplase in our cohort, suggesting that the fibrin specificity of thrombolytic agents may play a pivotal role in its development.

Heparin-induced thrombocytopenia (HIT) is a severe immunological adverse effect of heparin therapy, characterized by thrombocytopenia and unpredictable thromboembolic complications. Rapid discontinuation of heparin and replacement by an alternative anticoagulant such as danaparoid is mandatory. We report the case of a 45-year-old woman with uterine sarcoma and acute HIT, who experienced treatment failure with danaparoid. Despite danaparoid dosage escalation, anti-Xa activity remained subtherapeutic, resulting in clinical deterioration. Acquired antithrombin (AT) deficiency in the context of cancer and HIT -associated disseminated intravascular coagulation was then diagnosed. The administration of AT concentrate corrected AT levels thereby restoring therapeutic anti-Xa levels. This is the first reported case of danaparoid failure due to a documented AT deficiency demonstrating the potential efficacy of AT supplementation in this context. This case highlights the importance of monitoring AT levels in HIT patients when danaparoid activity is below the therapeutic range despite adjusted dosing.

Background Intravenous thrombolysis (IVT) failure in acute ischemic stroke (AIS) due to large vessel occlusion (LVO) is frequent but its causes remain elusive. Several non-exclusive mechanisms have been proposed to explain IVT failure, including failed delivery of tPA and inhibition of its activity. We investigated whether biologically relevant intrathrombus concentrations of t-PA were achieved in failed IVT in patients with LVO AIS, and whether neutrophil extracellular traps (NETs) contributed to IVT failure. Methods In this cohort study, a total of 205 thrombi from AIS patients with LVO were analyzed. 83 of these thrombi were compared for tPA content and 53 for their susceptibility to ex vivo thrombolysis according to IVT status. An additional subset of 69 AIS thrombi was used to decipher if and how NETs interfere with intrathrombus fibrinolysis. Results AIS thrombi from IVT patients contained more tPA than those from no-IVT patients (0.209 vs 0.093 µg/mg of thrombus, p<0.0001). Plasminogen and tPA in AIS thrombi were found in association with fibrin and NETs. The ability of NETs to bind tPA and plasminogen, titrating them away from fibrin, was confirmed in a microfluidic model of thrombosis. While ex vivo addition of plasminogen did not cause lysis of either no-IVT or IVT thrombi, combining plasminogen with DNase 1 helped translate the increased tPA content of IVT thrombi into increased thrombolysis. We further show that DNase 1 enables tPA- and plasmin-mediated thrombolysis by eliminating fibrinolysis inhibitors from AIS thrombi. Conclusions These results indicate that intrathrombus tPA concentrations reached in failed IVT bear a therapeutic potential that is however impaired by NETs, which favor intrathrombus retention of fibrinolysis inhibitors and compete with fibrin for tPA and plasminogen binding. Our results stress the interest of DNase 1 to enhance the efficacy of current IVT tPA regimens. What is new? What are the clinical implications? ### Competing Interest Statement The authors have declared no competing interest.

Background:Factor (F)XI deficiency is a rare bleeding disorder with a poor correlation between bleeding tendency and FXI level. Management of pregnant women with FXI deficiency is not clearly established, especially regarding neuraxial analgesia (NA). Objectives:A retrospective multicenter observational study was conducted in French hemostasis centers on pregnant women with FXI of <60 IU/dL. Methods:Data to report were (i) FXI levels before pregnancy and at time of delivery, (ii) type of NA and delivery management modalities, and (iii) possible complications related to NA and bleeding complications. Results:Three hundred fourteen pregnancies in patients with FXI deficiency of <60 IU/dL were reported (from 20 centers); among them, 199 NA procedures have been completed (137 epidurals and 61 spinals, 1 had both). The period of childbirth was mostly from 2014 to 2020 (281/314; 89.5%). Congenital FXI deficiency was established with certainty by investigators in 32.8% patients (n = 103). Previous bleedings were described in 20.4% of the patients (64/314; 45.3% cutaneous, 31.3% gynecologic, and 15.6% postsurgical). Thirteen deliveries had an NA procedure with FXI of <30 IU/dL, 42 with FXI of 30-40 IU/dL, and 118 with FXI of 40-60 IU/dL. Median FXI levels at delivery in the epidural and spinal groups were not significantly different but were significantly lower in the group without NA by medical staff contraindications. There were no complications related to NA. A 17.5% postpartum hemorrhage or excessive postpartum bleeding incidence was reported, which is consistent with previous data. Conclusion:Our data support the use of a 30 IU/dL FXI threshold for NA, as suggested by the French proposals published in August 2023.

Background: Preoperative identification of patients with hemostasis abnormalities leading to an increased bleeding risk is based on routine hemostasis tests: prothrombin time (PT), activated partial thromboplastin time (APTT), and platelet count. Because of their low predictive performance, guidelines recommend replacing them with structured bleeding risk questionnaires, but none is validated in this population. Objectives: To assess the diagnostic accuracy of 3 strategies, performed at the pre- anesthesia visit before scheduled interventions, and to identify patients with hemostasis abnormalities leading to an increased bleeding risk Methods: A multicenter study was performed in 7 French academic hospitals, involving patients scheduled for surgical intervention, without antiplatelet/anticoagulant treatment. The 3 strategies consisted of 1-a structured screening questionnaire; 2-PT, APTT, and platelet count ordered in selected patients; and 3-systematic PT, APTT, and platelet count. The reference standard comprised von Willebrand factor activity/antigen, factor (F)VIII, FIX, FXI, platelet function analyzer, and, when required, FII, FV, FX, and FVII and hemostasis consultation. Results: Eighteen (1.2%) of 1484 patients had a hemostasis abnormality leading to an increased bleeding risk according to reference standard. In the overall cohort, sensitivity of the questionnaire-based strategy was 50% (95% CI, 26%-74%; specificity, 87% [95% CI, 85%-88%]); sensitivity was 0% (95% CI, 0%-41%) in men vs 82% (95% CI, 48%98%) in women. For selective routine tests, sensitivity was 33% (95% CI, 13%-59%) and specificity 97% (95% CI, 96%-98%). Corresponding values for systematic routine tests were 44% (95% CI, 22%-69%) and 93% (95% CI, 91%-94%). Conclusion: Sensitivity was low for all 3 strategies investigated. The structured screening questionnaire had clinically acceptable diagnostic accuracy only in women.

Cerebral venous sinus thrombosis (CVST) is an uncommon venous thromboembolic event accounting for <1% of strokes resulting in brain parenchymal injuries. JAK2V617F mutation, the most frequent driving mutation of myeloproliferative neoplasms has been reported to be associated with worse clinical outcomes in patients with CVST. We investigated whether hematopoietic JAK2V617F expression predisposes to specific pathophysiological processes and/or worse prognosis after CVST. Using an in vivo mouse model of CVST, we analyzed clinical, biological and imaging outcomes in mice with hematopoietic-restricted Jak2V617F expression, compared to Jak2WT mice. In parallel, we studied a human cohort of JAK2V617F-positive or negative CVST.Early after CVST, mice with hematopoietic Jak2V617F expression had increased adhesion of platelets and neutrophils in cerebral veins located in the vicinity of CVST. On day 1, Jak2V617F mice had a worse outcome characterized by significantly more frequent and severe intracranial hemorrhages (ICH) and higher mortality rates. Peripheral neutrophil activation was enhanced, as indicated by higher circulating platelet-neutrophil aggregates, upregulated CD11b expression, and higher myeloperoxydase (MPO) plasma level. Concurrently, immunohistological and brain homogenates analysis showed higher neutrophil infiltration and increased blood-brain-barrier disruption. Similarly, JAK2V617F-positive CVST patients tended to present higher thrombotic burden and had significantly higher SII, a systemic thrombo-inflammatory marker, compared to JAK2V617F-negative patients.In mice with CVST, our study corroborates that Jak2V617F mutation leads to a specific pattern including increased thrombotic burden, ICH and mortality. The exacerbated thrombo-inflammatory response, observed both in mice and JAK2V617F-positive patients, could contribute to hemorrhagic complications.

Background: Scientific and clinical interest in extracellular vesicles (EVs) is growing. EVs that expose tissue factor (TF) bind factor VII/VIIa and can trigger coagulation. Highly procoagulant TF-exposing EVs are detectable in the circulation in various diseases, such as sepsis, COVID-19, or cancer. Many in-house and commercially available assays have been developed to measure EV-TF activity and antigen, but only a few studies have compared some of these assays. Objectives: The International Society on Thrombosis and Haemostasis Scientific and Standardization Committee Subcommittee on Vascular Biology initiated a multicenter study to compare the sensitivity, specificity, and reproducibility of these assays. Methods: Platelet-depleted plasma samples were prepared from blood of healthy donors. The plasma samples were spiked either with EVs from human milk or EVs from TF-positive and TF-negative cell lines. Plasma was also prepared from whole human blood with or without lipopolysaccharide stimulation. Twenty-one laboratories measured EV-TF activity and antigen in the prepared samples using their own assays representing 18 functional and 9 antigenic assays. Results: There was a large variability in the absolute values for the different EV-TF activity and antigen assays. Activity assays had higher specificity and sensitivity compared with antigen assays. In addition, there was a large intra-assay and interassay variability. Functional assays that used a blocking anti-TF antibody or immunocapture were the most specific and sensitive. Activity assays that used immunocapture had a lower coefficient of variation compared with assays that isolated EVs by high-speed centrifugation. Conclusion: Based on this multicenter study, we recommend measuring EV-TF using a functional assay in the presence of an anti-TF antibody.

BACKGROUND:Myeloproliferative neoplasms (MPNs) are characterized by a high rate of thrombotic complications that contribute to morbidity and mortality. MPN-related thrombogenesis is assumed to be multifactorial, involving both procoagulant and proinflammatory processes. Whether impaired fibrinolysis also participates in the prothrombotic phenotype of MPN has been poorly investigated. OBJECTIVES:We determined whether MPN, particularly JAK2V617F-positive MPN, is associated with fibrinolytic changes. METHODS:Tissue-type plasminogen activator (tPA)-mediated fibrinolysis was evaluated both in whole blood and plasma from mice with a hematopoietic-restricted Jak2V617F expression compared with wild-type (WT) mice (Jak2WT) using (1) halo clot lysis, (2) front lysis, and (3) plasmin generation assays. tPA clot lysis assay was performed in the plasma from 65 MPN patients (JAK2V617F mutation, n = 50; CALR mutations, n = 9) compared with 28 healthy controls. RESULTS:In whole blood from Jak2V617F mice, we observed a decreased fibrinolysis characterized by a significantly lower halo clot lysis rate compared with Jak2WT (95 ± 22 vs 147 ± 39 AU/min; P < .05). Similar results were observed in plasma (halo clot lysis rate, 130 ± 27 vs 186 ± 29 AU/min; front lysis rate, 2.8 ± 1.6 vs 6.1 ± 1.2 μm.min-1; P < .05). Plasmin generation was significantly decreased both in plasma clots and standardized fibrin clots from Jak2V617F mice compared with Jak2WT mice. Among MPN patients, impaired tPA-related fibrinolysis with prolonged clot lysis time was observed in JAK2V617F and CALR patients. Plasminogen activator inhibitor-1 and α2-antiplasmin were significantly increased in plasma from JAK2V617F patients compared with controls. CONCLUSION:Our results suggest that impaired tPA-mediated fibrinolysis represents an important prothrombotic mechanism in MPN patients that requires confirmation in larger studies.

BACKGROUND:Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a complication of adenoviral-based vaccine against SARS-CoV-2 due to prothrombotic immunoglobulin (Ig) G antibodies to platelet factor 4 (PF4) and may be difficult to distinguish from heparin-induced thrombocytopenia (HIT) in patients treated with heparin. OBJECTIVES:We assessed the usefulness of competitive anti-PF4 enzyme immunoassays (EIAs) in this context. METHODS:The ability of F(ab')2 fragments of 1E12, 1C12, and 2E1, 3 monoclonal anti-PF4 antibodies, to inhibit the binding of human VITT or HIT antibodies to PF4 was evaluated using EIAs. Alanine-scanning mutagenesis was performed to define the amino acids involved in the interactions between the monoclonal antibodies and PF4. RESULTS:A strong inhibition of VITT IgG binding to PF4 was measured with 1E12 (median inhibition, 93%; n = 8), whereas it had no effect on the binding of HIT antibodies (median, 6%; n = 8). In contrast, 1C12 and 2E1 inhibited VITT (median, 74% and 76%, respectively) and HIT antibodies (median, 68% and 53%, respectively) binding to PF4. When a competitive anti-PF4 EIA was performed with 1E12 for 19 additional VITT samples, it strongly inhibited IgG binding to PF4, except for 1 patient, who had actually developed HIT according to the clinical history. Epitope mapping showed that 1E12 interacts with 5 key amino acids on PF4, of which 4 are also required for the binding of human VITT antibodies, thus explaining the competitive inhibition. CONCLUSION:A simple competitive anti-PF4 EIA with 1E12 could help confirm VITT diagnosis and distinguish it from HIT in patients when both diagnoses are possible.

Therapeutic plasma exchange (TPE) has been proposed to remove heparin-induced thrombocytopenia (HIT) antibodies before planned thoracic surgery in patients with acute HIT and to allow brief re-exposure to heparin during surgery. In patients on extracorporeal membrane oxygenation (ECMO), simultaneous administration of TPE and alternative nonheparin anticoagulant therapies is challenging. We report 2 patients on ECMO with acute HIT who underwent repeated TPE to enable cardiothoracic surgery with the use of heparin. In both cases, serial monitoring of HIT antibody titer and heparin-induced platelet activation assay (HIPA) was performed. The effect of adding exogenous platelet factor 4 (PF4) in the HIPA was also tested. Negative anti-PF4/H IgG levels were achieved after 5 and 3 TPE sessions, respectively and patients could beneficiate from surgery with brief heparin re-exposure without any thrombotic complication. Negative HIPA results were obtained before negative anti-PF4/H IgG in one patient but remained positive in the other despite very low antibody titers. The addition of PF4 in HIPA led to more contrasted results for the two patients. Serial HIT screening including immunological and functional assays is necessary to closely monitor TPE in acute HIT patients on ECMO who require surgery. The addition of PF4 in HIPA could help detect clinically relevant platelet-activating antibodies and guide re-exposure to heparin.

IntroductionAlthough many studies have underscored the importance of T cells, phenotypically and functionally, fewer have studied the functions of myeloid cells in COVID disease. In particular, the potential role of myeloid cells such as monocytes and low-density neutrophils (LDNs) in innate responses and particular in the defense against secondary bacterial infections has been much less documented.MethodsHere, we compared, in a longitudinal study, healthy subjects, idiopathic fibrosis patients, COVID patients who were either hospitalized/moderate (M-) or admitted to ICU (COV-ICU) and patients in ICU hospitalized for other reasons (non-COV-ICU).ResultsWe show that COVID patients have an increased proportion of low-density neutrophils (LDNs), which produce high levels of proteases (particularly, NE, MMP-8 and MMP-9) (unlike non-COV-ICU patients), which are partly responsible for causing type II alveolar cell damage in co-culture experiments. In addition, we showed that M- and ICU-COVID monocytes had reduced responsiveness towards further live Pseudomonas aeruginosa (PAO1 strain) infection, an important pathogen colonizing COVID patients in ICU, as assessed by an impaired secretion of myeloid cytokines (IL-1, TNF, IL-8,…). By contrast, lymphoid cytokines (in particular type 2/type 3) levels remained high, both basally and post PAO1 infection, as reflected by the unimpaired capacity of T cells to proliferate, when stimulated with anti-CD3/CD28 beads.DiscussionOverall, our results demonstrate that COVID circulatory T cells have a biased type 2/3 phenotype, unconducive to proper anti-viral responses and that myeloid cells have a dual deleterious phenotype, through their LDN-mediated damaging effect on alveolar cells and their impaired responsiveness (monocyte-mediated) towards bacterial pathogens such as P. aeruginosa.

Background: Light transmission aggregation (LTA) is used widely by the clinical and research communities. Although it is a gold standard, there is a lack of interlaboratory harmonization. Objectives: The primary objective was to assess whether sources of activators (mainly adenosine diphosphate [ADP], collagen, arachidonic acid, epinephrine, and thrombin receptor activating peptide6) and ristocetin contribute to poor LTA reproducibility. The secondary objective was to evaluate interindividual variability of results to appreciate the distribution of normal values and consequently better interpret pathologic results.Methods: An international multicenter study involving 28 laboratories in which we compared LTA results obtained with center-specific activators and a comparator that we supplied. Results: We report variability in the potency (P) of activators in comparison with the comparator. Thrombin receptor activating peptide 6 (P, 1.32-2.68), arachidonic acid (P, 0.87-1.43), and epinephrine (P, 0.97-1.34) showed the greatest variability. ADP (P, 1.04-1.20) and ristocetin (P, 0.98-1.07) were the most consistent. The data highlighted clear interindividual variability, notably for ADP and epinephrine. Four profiles of responses were observed with ADP from high-responders, intermediate-responders, and low-responders. A fifth profile corresponding to nonresponders (5% of the individuals) was observed with epinephrine.Conclusion: Based on these data, the establishment and adoption of simple standardization principles should mitigate variability due to activator sources. The observation of huge interindividual variability for certain concentrations of activators should lead to a cautious interpretation before reporting a result as abnormal. Confidence can be taken from the fact that difference between sources is not exacerbated in patients treated with antiplatelet agents.