Sickle Cells

This blood film is from a patient with homozygous Sickle Cell Anaemia. The HbS forms linear 'tactoids' which distort the cell into the characteristic shape. Initially, this is a reversible change, but eventually it becomes irreversible, and the cell is either removed in the reticulo-endothelial system, or becomes physically stuck within a small blood vessel, causing obstruction, followed by more sickling, and eventual infarction. This is the basis of the 'painful crisis'. Heterozygotes do not sickle, except when extremely hypoxic. Target cells are frequently seen in most haemoglobinopathies, and the erythroblasts occur because of the rapid haemolysis and early release from the marrow. The patients are frequently hyposplenic, so that the nucleus is not removed very rapidly.