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Thrombocytopaenia
Essentials
- 1
A low platelet count detected on automated blood count should always be confirmed by examination of the blood film prior to further investigation or treatment.
- 2
The cause of isolated thrombocytopaenia can often be determined by a careful history and physical examination in addition to assessment of the full blood count (FBC) and blood film.
- 3
Platelet transfusion is unnecessary in the management of the thrombocytopaenic patient unless the platelet count is extremely low or there is ongoing bleeding.
- 4
In the absence of other clotting disorders or abnormal platelet function, bleeding in the thrombocytopaenic patient is often amenable to local measures of haemostasis.
Introduction
Thrombocytopaenia is defined as a reduction in the number of circulating platelets, the normal circulating platelet count being 150 to 400 × 10 9 /L. It is the most common cause of abnormal bleeding. Like anaemia, thrombocytopaenia itself is not a diagnosis but rather a manifestation of another underlying disease process.
In the emergency department setting, thrombocytopaenia may present as an incidental finding on a routine blood count or may be diagnosed in the context of abnormal bleeding. In most cases the underlying aetiology can be determined by a careful history and physical examination combined with interpretation of the blood count.
Aetiology
The clinically important causes of thrombocytopaenia are outlined in Box 13.3.1 . Diagnoses are classified by pathological process. It should be noted that more than one pathological process may be present. The causes can be divided into three different groups: pseudothrombocytopaenia, increased destruction of platelets and reduced production of platelets.
Box 13.3.1
Causes of thrombocytopaenia
Pseudothrombocytopaenia
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Platelet clumping
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Collection into anticoagulant (ethylenediaminetetraacetic acid)
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Platelet agglutinins
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Giant platelets
Increased platelet destruction
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Immune
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Primary
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Idiopathic thrombocytopaenic purpura
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Secondary
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Autoimmune thrombocytopaenia associated with other disorders
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Graves disease, Hashimoto thyroiditis, systemic lupus erythematosus
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HIV-related thrombocytopaenia
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Drug-induced thrombocytopaenia
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Heparin, gold salts, quinine/quinidine, sulphonamides, rifampicin, H2 blockers, indomethacin, carbamazepine, valproic acid, ticlopidine, clopidogrel, monoclonal antibodies (infliximab, efalizumab, rituximab)
-
Post-transfusion purpura
-
-
Non-immune
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Thrombotic thrombocytopaenic purpura—haemolytic uraemic syndrome
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Pregnancy
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Gestational benign thrombocytopaenia
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Pre-eclampsia/haemolysis, elevated liver enzymes, low platelets
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Disseminated intravascular coagulation
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Decreased platelet production
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Congenital
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Thrombocytopaenia with absent radius, Wiskott-Aldrich syndrome
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Fanconi anaemia
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Acquired
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Viral infection
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Epstein-Barr virus, rubella, dengue fever
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Marrow aplasia
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Malignant bone marrow infiltrates
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Chemotherapeutic agents
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Radiation therapy
-
-
Abnormal distribution and dilution
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Splenic sequestration (hypersplenism)
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Splenic enlargement
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Hypothermia
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Massive blood transfusion
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Pseudothrombocytopaenia
Pseudothrombocytopaenia results from an underestimation of the platelet count as measured by an automated particle counter. The most common mechanism is platelet clumping. Clumping is most often due to the anticoagulant ethylenediaminetetraacetic acid (EDTA) but may also result from autoantibodies, such as cold agglutinins. The presence of giant platelets and platelet satellitism may also yield falsely low automated platelet counts.
Any case of thrombocytopaenia found on an automated blood count should be confirmed by examination of the peripheral smear prior to further investigation or treatment.
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