The study is being conducted to validate the clinical performance of the T-TAS 01 HD assay for measurement of thrombogenicity in patients with thrombocytopenia receiving a platelet transfusion.

This study will measure the improvement in thrombogenicity following platelet transfusion in patients with thrombocytopenia, using the T-TAS 01 HD assay, with a comparison with clinical truth, defined as the confirmation of increased platelet count attributed to platelet transfusion. The study will be conducted at a minimum of 3 locations in the United States and will enroll up to 90 subjects with thrombocytopenia and 50 healthy control subjects. The following subject populations will be enrolled into the study (enrollment numbers indicated in parentheses):

• Ostensibly healthy subjects with a normal platelet count and without a history of hemostasis abnormalities, for establishing expected values for quality control (N = up to 50)
• Subjects with thrombocytopenia who are planned to receive a platelet transfusion who have pre-transfusion and post-transfusion blood samples collected for testing (N = 50; up to 90 will be enrolled in the event that some subjects do not receive platelet transfusions after enrollment) Subjects will be recruited prospectively, and informed consent will be obtained after confirmation that the enrollment criteria described in Section 5a are satisfied. Blood samples will be collected after enrollment, and subject participation will be complete after all blood samples are collected and all necessary information is collected to complete the case report form (CRF). Blood sample testing with the T-TAS 01 and thromboelastography (TEG) assays will occur locally at each investigational site. Other required laboratory measurements (i.e. CBC) will be performed either locally or remotely, depending on the local availability.

Healthy Donors:

Inclusion Criteria:

• Males and females age 18 years or older.
• Able and willing to provide written informed consent.

Exclusion Criteria:

• Hospitalization or doctor's visits within prior 30 days, except for routine checkup/physical examination.
• Use of antiplatelet therapy within the past 14 days, e.g. aspirin, clopidogrel, prasugrel, ticagrelor, cilostazol.
• Use of anticoagulant drugs within the past 14 days, e.g. heparin, bivalirudin, warfarin, rivaroxaban, and apixaban.
• Use of certain nonsteroidal anti-inflammatory drugs (NSAIDs) that inhibit COX-1 such as rofecoxib, etc. within the past 14 days, unless confirmed to not inhibit platelet activity (such as celecoxib).
• History of anemia.
• Known thrombocytopenia (platelet count < 100,000/μL).
• Significant renal dysfunction (eGFR < 30 mL/min/1.73 m2) or dialysis.
• History of platelet disorders e.g. von Willebrand factor deficiency, Glanzmann's thrombasthenia or Bernard-Soulier syndrome.
• History of hemophilia or bleeding disorders.
• History of clinically significant bleeding requiring physician consultation or visit to healthcare facility.
• Females who are in the last trimester of pregnancy or are breastfeeding.
• Known active gastrointestinal disease including peptic ulcers, gastro-esophageal reflux disease (GERD), and hyperacidity.
• Currently participating in a study involving an investigational drug or compound known to affect coagulation or hemostasis.
• Subjects with significant past medical history as determined by the Investigator that would pose safety concerns or interfere with the study goals.

Thrombocytopenia Patients

Inclusion Criteria:

• Males and females age 18 years or older.
• Known thrombocytopenia, which may be attributed to any of the following:
• Immune thrombocytopenia (ITP)
• Lupus
• Rheumatoid arthritis
• Aplastic anemia
• Thrombotic thrombocytopenic purpura (TTP)
• Disseminated intravascular coagulation (DIC)
• Heparin induced thrombocytopenia (HIT)
• Vaccine-induced thrombotic thrombocytopenia (VITT)
• Infection
• Surgery
• Cancer
• Other etiologies including trauma, portal hypertension, liver disease, etc.
• Platelet count < 90,000/μL, confirmed by pre-transfusion CBC
• Planned platelet transfusion.
• Able and willing to provide written informed consent

Exclusion Criteria:

• Use of antiplatelet therapy within the past 14 days, e.g. aspirin, clopidogrel, prasugrel, ticagrelor, cilostazol, abciximab, eptifibatide within the past 14 days.
• Use of certain nonsteroidal anti-inflammatory drugs (NSAIDs) known to affect platelet function such as rofecoxib, etc. within the past 14 days, unless confirmed to not inhibit platelet activity (such as celecoxib).
• Surgical procedure on the same day as the baseline blood sample collection and testing
• Surgical procedure after baseline sample collection and testing, and prior to completion of all post-transfusion blood sample collection and testing
• Significant renal dysfunction (eGFR < 30 mL/min/1.73 m2) or dialysis.
• History of platelet disorders e.g. von Willebrand factor deficiency, Glanzmann thrombasthenia or Bernard-Soulier syndrome.
• History of hemophilia or bleeding disorders.
• Females who are in the last trimester of pregnancy or are breastfeeding.
• Known active gastrointestinal disease including peptic ulcers, gastro-esophageal reflux disease (GERD), and hyperacidity.
• Currently participating in a study involving an investigational drug or compound known to affect coagulation or hemostasis.
• Subjects with significant past medical history as determined by the Investigator that would pose safety concerns or interfere with the study goals.

• Ostensibly healthy subjects with a normal platelet count and without a history of hemostasis abnormalities, for establishing expected values for quality control (N = up to 50)
• Subjects with thrombocytopenia who are planned to receive a platelet transfusion who have pre-transfusion and post-transfusion blood samples collected for testing (N = 50; up to 90 will be enrolled in the event that some subjects do not receive platelet transfusions after enrollment)