Thrombocytopenia is defined as a low circulating platelet count (<150,000 per microlitre). 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/rheumatological conditions.
The causes of thrombocytopenia are diverse, making epidemiological generalisations difficult. However, immune thrombocytopenia (ITP) is typically an illness of young women. The apparent appearance of ITP in other patient groups should prompt a high index of suspicion for an alternative diagnosis: for example, non-Hodgkin's lymphoma, drug effect, or myelodysplastic syndrome.
A complete history, physical examination, review of the FBC, 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's lymphoma
- Non-Hodgkin's lymphoma
- Miliary tuberculosis
- Disseminated intravascular coagulation (DIC)
- Haemolysis, 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, antiepileptic drugs, antibiotics, or chemotherapies
- Alcohol ingestion
- B12 deficiency
- Folate deficiency
- Gestational thrombocytopenia
- Multiple myeloma
- Bone marrow fibrosis
- Thrombotic thrombocytopenic purpura (TTP)
- Haemolytic uraemic syndrome (HUS)
- Cyclic thrombocytopenia
- Wiskott-Aldrich syndrome
- MYH9-related disorders, including May-Hegglin anomaly
- Bernard-Soulier syndrome
- Gaucher's disease
- Hashimoto's thyroiditis
- Aplastic anaemia
- Paroxysmal nocturnal haemoglobinuria (PNH)
- Familial platelet disorder with germline RUNX1 mutation
- Thrombocytopenia due to germline ANKRD26 mutation
- Thrombocytopenia due to germline ETV6 mutation
- Practice bulletin no. 207: thrombocytopenia in pregnancy
- American Society of Hematology 2019 guidelines for immune thrombocytopenia
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