Reduced platelet count

Thrombocytopenia is defined as platelet count <150 x 109/L. Although there is no precise platelet count at which a patient will or will not bleed, most patients with a count >50 x 109/L are asymptomatic. The risk of spontaneous haemorrhage increases significantly <20 x 109/L. Purpura is the most common presenting symptom and is usually found on the lower limbs and areas subject to pressure. May be followed by bleeding gums, epistaxis or more serious life-threatening haemorrhage. A patient with newly diagnosed severe thrombocytopenia with or without purpura is a medical emergency and should be admitted for further investigation and treatment.

Confirm low platelet count by examination of the blood sample for clots and the blood film for platelet aggregates (causing pseudothrombocy-topenia). History and examination will determine the clinical severity of the thrombocytopenia and should also reveal the duration of symptoms, presence of any prodromal illness, causative medication or underlying disease.

Determine whether the cause of thrombocytopenia is failure of production or increased consumption. FBC may be helpful as the mean platelet volume (MPV) is often elevated in the latter group (large platelets may also be seen on the blood film). May also reveal additional haematological abnormalities (normocytic anaemia or neutropenia) suggestive of a bone marrow disorder. A coagulation screen should also be performed. Examination of the bone marrow is the definitive investigation in all patients with moderate or severe thrombocytopenia—may reveal normal megakaryocytes or compensatory hyperplasia in peripheral destruction syndromes or marrow hypoplasia or infiltration. Tests for platelet antibodies are unreliable but an autoimmune screen may be helpful to exclude lupus.

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