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Appearance of Normal RBCs
In a normal blood sample prepared for viewing under the microscope, the RBCs are 7–8 micrometers (µm) in diameter. They are very similar in size to each other and have a smooth surface. RBCs are usually dark red. (However, because of their biconcave shape, the center of the cell may look lighter when viewed in the microscope.) Mature RBCs (the kind seen in a blood sample in a microscope) do not have a nucleus. WBCs are often larger than RBCs and have nuclei that are irregularly shaped and darkly stained.

The blood test data use the following abbreviations.

.normal RBCs
Image credit: CDC/Dr. Mae Melvin

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