Appearance:
Normoblasts are the nucleated precursors of eruthrocytes. The cytoplasm changes with the increasing maturity from basophilic, to polychromatophilic to orthochromatic. The nucleus is coarse to pycnotic, compact and partially eccentric. In peripheral blood, the normoblast count is calculated relative to 100 leukocytes.
Counting:
In peripheral blood, the normoblast count is calculated relative to 100 leukocytes. If more than 3-5 normoblasts per 100 leukocytes are found, the white blood count must be corrected (correction for normoblasts).
An example:
- Automatically-counted leukocytes = 47.7 x 109/L
- Microscopically 15 normoblasts per 100 leukocytes are found
- Corrected white blood count = (47.7 / (100+15)) x 100 = 41.5 x 109/L.
Occurrence:
The occurrence of normoblasts in the peripheral blood is always pathological. They can be observed in the accelerated erythropoiesis (e.g. in severe hemolysis), in bone marrow metastatic disease, or in extramedullary blood formation.