Required section · Section 2 of 6
Basic mental model: the normal field has controlled variation
A normal mature red blood cell, or RBC, is a discocyte. In a Romanowsky-stained monolayer it is round with central pallor occupying roughly the central one-third of the diameter. A normal RBC diameter is approximately 7 to 8 micrometers, averaging near 7.5 micrometers. This is a visual baseline, not a micrometer measurement made by the smear.
A normal mature small lymphocyte nucleus is approximately the diameter of a normal RBC and is a practical same-field size reference. Compare the platelet to that reference when deciding whether it is ordinary, large, or approaching giant. A platelet approaching or exceeding RBC diameter is descriptively giant, rather than a category defined here by one universal cutoff. This comparison reduces overcalling of normal size variation.
Normal blood is not visually identical cell by cell. Polychromasia is increased gray-blue staining of young RBCs from residual RNA; anisocytosis is variation in RBC size; and poikilocytosis is variation in RBC shape. Mild variation can be background. Describe a specific abnormal shape when present rather than using poikilocytosis alone.
A repeatable normal-background scan
Choose the monolayer
Work just behind the feathered edge where RBCs are single layered and barely touching.
Anchor size
Use a small lymphocyte nucleus as an approximate RBC-diameter reference.
Read RBC background
Assess discocyte shape, central pallor, and the expected low-level continuum of variation.
Scan platelets
Look across the monolayer and edge areas for distribution, clumps, satellitism, and unusually large platelets.
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