Thrombocytopenia is defined as a low circulating platelet count (<150,000 per microliter). Platelet life span is normally approximately 5 days, with continual renewal.
Thrombocytopenia results from either a reduced production of platelets in the bone marrow, increased clearance, sequestering of platelets in the spleen, or dilution.
The differential diagnosis for a patient with new thrombocytopenia is broad and includes primary bone marrow disorders, chronic liver disease, infection, drug-related adverse effects, occult malignancy, and autoimmune/rheumatologic conditions.
The causes of thrombocytopenia are diverse, making epidemiologic generalizations difficult. However, immune thrombocytopenia (ITP) increases with age and has a slight female preponderance. The apparent appearance of ITP in other patient groups should prompt a high index of suspicion for an alternate diagnosis: for example, non-Hodgkin lymphoma, drug effect, or myelodysplastic syndrome. ITP has an estimated incidence of approximately 2 to 5 cases per 100,000 in the general population.
A complete history, physical exam, review of the CBC, and peripheral smear are necessary to narrow down the differential diagnosis of thrombocytopenia. It is important to exclude artifact or pseudothrombocytopenia.
Bone marrow biopsy is performed if all other studies are inconclusive.
Primary ITP is diagnosed when there is no identifiable underlying condition following comprehensive patient evaluation.
- Metastatic malignancy
- Hodgkin lymphoma
- Non-Hodgkin lymphoma
- Miliary tuberculosis
- Disseminated intravascular coagulation (DIC)
- Hemolysis, elevated liver enzymes, low platelet count (HELLP)
- Cardiopulmonary bypass
- Immune thrombocytopenia (ITP)
- Systemic lupus erythematosus (SLE)
- Rheumatoid arthritis
- Antiphospholipid syndrome
- Dengue fever
- Zika virus infection
- Cytomegalovirus (CMV)
- Infectious mononucleosis
- Parvovirus B19
- Heparin-induced thrombocytopenia (HIT)
- Antimalarials, antiseizure drugs, antibiotics, or chemotherapies
- Alcohol ingestion
- B12 deficiency
- Folate deficiency
- Gestational thrombocytopenia
- Multiple myeloma
- Bone marrow fibrosis
- Thrombotic thrombocytopenic purpura (TTP)
- Hemolytic uremic syndrome (HUS)
- Cyclic thrombocytopenia
- Wiskott-Aldrich syndrome
- MYH9-related disorders, including May-Hegglin anomaly
- Bernard-Soulier syndrome
- Gaucher disease
- Hashimoto thyroiditis
- Aplastic anemia
- Paroxysmal nocturnal hemoglobinuria (PNH)
- Familial platelet disorder with germline RUNX1 mutation
- Thrombocytopenia due to germline ANKRD26 mutation
- Thrombocytopenia due to germline ETV6 mutation
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