Blood Film - Disorders

Disorders

Characteristic red blood cell abnormalities are anemia, sickle cell anemia and spherocytosis. Sometimes the microscopic investigation of the red cells can be essential to the diagnosis of life-threatening disease (e.g. TTP).

White blood cells are classified according to their propensity to stain with particular substances, the shape of the nuclei and the granular inclusions.

• Neutrophil granulocytes usually make up close to 80% of the white count. They have multilobate nuclei and lightly staining granules. They assist in destruction of foreign particles by the immune system by phagocytosis and intracellular killing.
• Eosinophil granulocytes have granules that stain with eosin and play a role in allergy and parasitic disease. Eos have a multilobate nucleus.
• Basophil granulocytes are only seen occasionally. They are polymorphonucleated and their granules stain dark with alkaline stains, such as haematoxylin. They are further characterised by the fact that the granules seem to overlie the nucleus. Basophils are similar if not identical in cell lineage to mast cells, although no conclusive evidence to this end has been shown. Mast cells are "tissue basophils" and mediate certain immune reactions to allergens.
• Lymphocytes have very little cytoplasm and a large nucleus (high NC ratio) and are responsible for antigen-specific immune functions, either by antibodies (B cell) or by direct cytotoxicity (T cell). The distinction between B and T cells cannot be made by light microscopy.
• Plasma cells are mature B lymphocytes that engage in the production of one specific antibody. They are characterised by light basophilic staining and a very eccentric nucleus.
• Other cells are white cell precursors. When these are very abundant it can be a feature of infection or leukemia, although the most common types of leukemia (CML and CLL) are characterised by mature cells, and have more of an abnormal appearance on light microscopy (additional tests can aid the diagnosis).