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Corrected Reticulocyte Percentage / Reticulocyte Production Index (RPI)

Adjusts reticulocyte count for anaemia and marrow maturation.

Corrected Reticulocyte Percentage / Reticulocyte Production Index (RPI)
Reticulocyte percentage
%
Measured hematocrit
%
Complete the fields above to see the result.

When to use

  • Assessing whether the bone marrow is responding appropriately to anaemia.

Formula

Corrected retic % = retic % x (Hct / 45). RPI = corrected retic % / maturation factor (Hct >=40:1.0; 35-39:1.5; 25-34:2.0; 20-24:2.5; <20:3.0).

Pearls and pitfalls

  • RPI <2 with anaemia points to reduced production (nutritional, marrow, or renal causes).
  • Maturation factor accounts for premature release of reticulocytes in anaemia.

References

  1. Hillman RS, Finch CA. Red Cell Manual. 7th ed. Philadelphia: FA Davis; 1996.