Polychromasia refers to macrocytic (large) red blood cells with a bluish tinge, due to residual RNA. These cells are likely reticulocytes, which are immature non-nucleated red cells which have only just extruded their nuclei.

This finding may occur in the context of haemolysis, though may also be seen during recovery following haemorrhage or bone marrow suppression (such as following cytotoxic chemotherapy).