The goal of this single-center, non-controlled, non-randomized exploratory clinical trial is To develop and validate a clinical-biological score (VISCOTHEM score) incorporating viscoelastometric tests parameters; based on an association study, and to establish a threshold that enables the prediction of the immediate risk of bleeding in haematology patients with severe thrombocytopenia (<20 G/L); with a view to selecting a population with a residual risk of bleeding of zero (NPV ≥ 95%, to achieve a residual probability of bleeding < 5%).

The score may incorporate variables identified in the literature as having a plausible causal relationship with the occurrence of bleeding (14,15), as well as viscoelastometric tests parameters, conventional haemostasis parameters and relevant clinical parameters. .

Participants will undergo an additional blood sample to standard care. The total volume of blood drawn will be 21.1 mL. The following analyses will be performed: Quantra®, Rotem®, blood count, platelets, immature platelet count, plasma prothrombin time, activated partial thromboplastin time, International Normalized Ratio, fibrinogen, urea, creatinin, albumin.

Inclusion Criteria:

• Adult patients;
• Who have been informed about the study and have freely given their informed consent to participate in the study;
• With a malignant haematological disorder or bone marrow failure, whether treated or untreated and at any stage of treatment;
• With central thrombocytopenia strictly below 20 G/L in a blood sample taken less than 72 hours ago and not having received a transfusion since;
• Admitted to a haematology day unit or inpatient ward, or being followed up at a haematology outpatient clinic;
• With or without active bleeding;
• Affiliated with or covered by a social security scheme.

Exclusion Criteria:

• Patients who have received at least one of the following treatments:
• Antiplatelet agents within 7 days prior to enrolment,
• Vitamin K antagonists within 7 days prior to enrolment,
• Direct oral anticoagulants within 72 hours prior to enrolment,
• Low molecular weight heparin within 24 hours prior to inclusion,
• Unfractionated heparin within 6 hours prior to inclusion,
• Bruton's tyrosine kinase inhibitor (ibrutinib, zanubrutinib or acalabrutinib) within 72 hours prior to inclusion;
• Patients with a history of thrombopathy;
• Patients with a history of haemostatic disorders carrying a risk of haemorrhage or thrombosis;
• Thrombocytopenia associated with immune thrombocytopenic purpura or disseminated intravascular coagulation;
• Patients already enrolled in the study;
• Pregnant or breastfeeding women;
• Patients under guardianship or curatorship;
• Patients who do not understand French;
• Patients under judicial protection.

The patients included will be selected from the entire cohort of patients with haematological malignancies:

• those admitted to the haematology day unit for treatment or assessment,
• or patients admitted to the haematology inpatient ward,
• or patients being monitored in the haematology outpatient clinic.