Reticulocyte Count

Physiology

  • Reticulocytes are Newly-Released RBC’s: they are slightly larger than mature RBC’s and have some residual ribosomal RNA -> presence of RNA allows for staining, with detection and counting

Technique

  • Normal Reticulocyte Percentage: 1-2%
  • Reticulocyte Production Index (RPI) = Reticulocyte Percentage x (Patient’s Hct/Normal Hct) x (1/RMT): corrects reticulocyte percentage for the degree of anemia (normalized to Hct 45%) and reticulocyte maturation time (RMT)

    • Use Normal Hct = 45%
    • RMT

      • Hct 45% -> RMT = 1.0 days
      • Hct 15% -> RMT = 2.5 days
    • Reticulocyte Production Index > or = to 2.5%: indicates adequate bone marrow response to anemia [MEDLINE]

      • Acute/Subacute Hemorrhage: note that acute hemorrhage may not result in an increased RPI, due to the time that it takes to increase epo synthesis and increase bone marrow RBC production
      • Hemolytic Anemia
    • Reticulocyte Production Index <2.5%: indicates inadequate bone marrow response to anemia [MEDLINE]

      • Chronic Anemia
      • Hypoproliferative Anemia: such as iron deficiency, marrow hyporesponsiveness, aplasia, etc
      • Maturation Disorder: such as vitamin B2 deficiency, etc

References

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