Expansion
Biconcave anucleate discs with central pallor, and anucleate platelet fragments
Expansion
Erythrocytes
- Biconcave discs of about 7 to 8 micrometres, conveniently similar to the diameter of a small lymphocyte nucleus, which serves as an internal size reference on a film
- Anucleate and without organelles in mammals, maximising haemoglobin content and deformability
- Central pallor of about one third of the diameter, reflecting the biconcavity
- Lifespan 120 days
Descriptive terms
- Anisocytosis: variation in size; quantified as the red cell distribution width
- Poikilocytosis: variation in shape
- Hypochromia: increased central pallor, indicating reduced haemoglobin
- Polychromasia: blue-grey cells, which are reticulocytes retaining ribosomal RNA
Platelets
- Anucleate cytoplasmic fragments of 2 to 3 micrometres, budded from megakaryocytes
- Contain alpha and dense granules
- Lifespan 7 to 10 days, with a third sequestered in the spleen
- Large platelets suggest increased turnover, as in immune thrombocytopenia
- Platelet clumping on an EDTA sample is the commonest cause of spurious thrombocytopenia, and is identified by examining the film