Polychromasia on a blood smear indicates the presence of what?

• A. Mature red blood cells
• B. Immature red blood cells with residual RNA
• C. Spherocytes
• D. Platelets

Answer: (B)

Polychromasia signals the presence of immature red blood cells, known as reticulocytes, in the bloodstream. These young cells still contain residual ribosomal RNA, which stains blue with standard blood smear stains. That lingering RNA gives the red cells a mixed, bluish tint—polychromasia—and shows the bone marrow is actively producing red cells in response to anemia or increased destruction.

Mature red blood cells lack RNA, so they appear a uniform pink without the blue coloration. Spherocytes are red cells that have become sphere-shaped due to membrane changes and don’t reflect RNA content. Platelets are not red blood cells and don’t contribute to polychromasia.