oPatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
Thrombocytopenia means a reduction in the platelet count below the normal lower limit, which is usually defined as 150 x 109/L . This can have a variety of causes, including a reduction in platelet production, a reduction in platelet survival, and dilution of platelet numbers resulting from the transfusion of platelet-poor blood.
Disorders affecting platelet production
- Megakaryocytic hypoplasia - underdevelopment of megakaryocytes which normally develop in bone marrow and fragment to produce platelets - usually of autoimmune or infectious origin.
- Thrombocytopenia/absent radii (TAR syndrome) - radial aplasia or hypoplasia and thrombocytopenia.
- Bernard-Soulier syndrome.
- Wiskott-Aldrich syndrome - an X-linked recessive disease characterised by thrombocytopenia,
lymphopenia and depressed cellular immunity, eczema, malignant lymphoma.
- May-Hegglin anomaly: thrombocytopenia, giant platelets and leukocyte inclusions (Döhle leukocyte inclusions).
- Congenital leukaemia - eg, in association with Down's syndrome.
- Fanconi's anaemia.
Decreased production (disorders of bone marrow)
See also separate article Bone Marrow and Bone Marrow Failure.
- Viral infections - eg, herpes simplex, cytomegalovirus, varicella-zoster, Epstein-Barr, rubella, enterovirus, mumps, hepatitis, HIV.
- Aplastic anaemia.
- Marrow infiltration by a malignancy - eg, leukaemia, lymphoma, myeloma, metastatic malignant disease.
- Drugs - eg, chemotherapy.
- Paroxysmal nocturnal haemoglobinuria.
- Megaloblastic anaemia.
- Miliary tuberculosis.
Decreased platelet survival
- Immune - idiopathic thrombocytopenia purpura, systemic lupus erythematosus, rheumatoid arthritis, sarcoidosis, antiphospholipid syndrome.
- Post-transfusion thrombocytopenic purpura (PTTP):
- Antigens on transfused platelets can lead to destruction of not just the transfused platelets but the patient's own platelets too.
- It starts about 10 days after transfusion but can last several weeks or even several months.
- Neonatal alloimmune thrombocytopenia (NAIT):
- Occurs when the mother produces antibodies against fetal platelets with paternal antigens.
- It is the most common cause of severe neonatal thrombocytopenia.
- It often follows an apparently uneventful pregnancy but the risk of intracranial haemorrhage is high and mortality is high too.
- Unlike haemolytic disease of the newborn, it commonly occurs in first pregnancies.
- Drug-induced - eg, heparin, penicillins, sodium valproate, carbamazepine.
- Thrombotic thrombocytopenic purpura.
- Haemolytic uraemic syndrome.
- Disseminated intravascular coagulation.
- Pregnancy - HELLP syndrome
- Cardiopulmonary bypass.
- Splenomegaly and hypersplenism, which may be associated with a variety of conditions - eg, cirrhosis, malaria, lymphoma.
- Kasabach-Merritt syndrome (cavernous haemangiomata with severe thrombocytopenia, and features of disseminated intravascular coagulation).
This is caused by transfusion of large volumes of blood which may be depleted of functioning platelets, resulting from prolonged storage.
- This can occur when platelets undergo a phenomenon called 'clumping'. In this situation, the platelets stick together, causing a false low reading when passed through an auto-analyser.
- The condition is caused by the action of ethylenediaminetetraacetic acid (EDTA) used as an anticoagulant. It occurs in about 0.1% of the population but can also be associated with infections with human immunodeficiency virus, rubella, cytomegalovirus, autoimmune disorders, neoplastic diseases, thrombotic disorders and possibly trauma.
- It is not indicative of a bleeding diathesis or platelet dysfunction. If an abnormally low platelet count is detected in the absence of a suggestive medical history, examination of a peripheral blood smear on a freshly taken specimen should be performed.
Assessment and management
A thorough history and examination are essential, with consideration of any history or indication of a possible underlying cause, and any history of abnormal bleeding (see also the separate article on Bleeding Disorders).
- FBC with differential and blood film: to assess the extent of the thrombocytopenia - and it may help in identifying the underlying cause.
- Investigations for any underlying cause suggested from the history and examination.
- Investigations regarding platelet function (see separate article Platelet Function Disorders (Thrombocytopathy).
- Bone marrow biopsy may be required.
- Investigations may need to include assessment of any possible complication of thrombocytopenia - eg, CT scan of the head if an intracranial haemorrhage is suspected.
Further investigations and management will depend on the suspected or confirmed underlying cause. See links in the section 'Causes', above.
Further reading & references
- The management of heparin-induced thrombocytopenia, British Committee for Standards in Haematology (2006)
- The ITP Support Association
- Thiagarajan P; Overview of Platelet Disorders, Medscape, May 2011
- Aster RH, Curtis BR, McFarland JG, et al; Drug-induced immune thrombocytopenia: pathogenesis, diagnosis, and management. J Thromb Haemost. 2009 Jun;7(6):911-8. Epub 2009 Apr 2.
- Hagerman R; Ethylenediaminetetraacetic Acid (EDTA)-Dependent Pseudothrombocytopenia: A Case Report of an Incidental but Important Finding, Priory.com 2009
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Laurence Knott
Dr Colin Tidy
Dr John Cox