FRCPath Haematology Part 2: Morphology RBC Morphology Overview Polychromasia

Polychromasia refers red cells of a range of colours. This is typically from the normal pink to the to the purplish colour which results from the uptake of eosin by haemoglobin and basic dye by residual RNA.

Causes:

  • Normal response to anaemia (provided sufficient erythropoietin / no haematinic deficiency)
  • Normal response to hypoxia
  • Polychromatic erythrocytes may be seen in primary myelofibrosis or carcinomatous spread to bone marrow. Such cells are not always macrocytic, and may be more deeply basophilic than reticulocytes.
Polychromasia. Peripheral blood film from a neonate with haemolytic disease of the newborn, showing marked polychromasia, numerous circulating erythroblasts and spherocytes. Note the marked range in colours of the red cells and red cell precursors, with the cytoplasm ranging from a purplish colour to the normal pink cytoplasm of mature, haemoglobinised RBCs. Many polychromatic cells are larger than normal RBCs, as they are actually reticulocytes. The staining of the residual RNA is what gives the distinct purplish hue.
Peripheral blood film from a neonate with haemolytic disease of the newborn, showing marked polychromasia, numerous circulating erythroblasts and spherocytes. Note the marked range in colours of the red cells and red cell precursors, with the cytoplasm ranging from a purplish colour to the normal pink cytoplasm of mature, haemoglobinised RBCs. Many polychromatic cells are larger than normal RBCs, as they are actually reticulocytes. The staining of the residual RNA is what gives the distinct purplish hue.
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