Left shift

Left shift or blood shift is an increase in the number of immature leukocytes in the peripheral blood, particularly neutrophil band cells. It is usually noted on microscopic examination of a blood smear. It is most often seen in the course of an active infection and during other severe illnesses such as hypoxia and shock. In these conditions, the bone marrow is thought to increase production to such an extent that immature forms begin to escape into the systemic circulation. Döhle bodies may also be present in the neutrophil's cytoplasm.

Less commonly, left shift may also refer to a similar phenomenon in severe erythroanemia, when reticulocytes and immature erythrocyte precursors appear in the peripheral circulation.