The Peripheral Blood Smear

Key points

• • A drop of blood is spread, stained and examined to assess the size, shape, colour and inclusions of the blood cells.
• • Target cells suggest thalassaemia, liver disease or a state after splenectomy (and are a less characteristic feature of iron deficiency), while spherocytes suggest hereditary spherocytosis or immune haemolysis.
• • Sickle cells indicate sickle-cell disease, and schistocytes (fragmented cells) indicate a microangiopathic process.
• • Tear-drop cells suggest marrow fibrosis, and bite cells with Heinz bodies suggest oxidative damage as in G6PD deficiency.
• • Hypersegmented neutrophils point to megaloblastic anaemia, and toxic granulation reflects inflammatory or infective stress rather than being specific for severe infection.
• • Rouleaux, in which red cells stack like coins, suggests a high level of plasma proteins as in multiple myeloma or chronic inflammation.