Observational StudyOptimizing the Diagnosis of Heparin Induced Thrombocytopenia

Inclusion Criteria:

• Patient with clinical suspicion of HIT by treating physician

Exclusion Criteria:

1. Less than 18 years of age;
2. Prior diagnosis of HIT ever;
3. Patient enrolled within preceding 100 days;
4. Functional/ confirmatory platelet activation results available at the time of enrollment;
5. Requiring cardio-pulmonary bypass or percutaneous cardiac angioplasty or any other cardiac or vascular surgery/procedure requiring intra-operative/procedural heparin administration planned within 30 days;
6. Unable to complete study follow up;
7. Unable to obtain consent (or proxy consent from substitute decision maker where applicable);
8. Life expectancy less than 30 days;
9. Greater than 72 hours from clinical suspicion of HIT and/or request for HIT anti-PF4 ELISA testing.