Reticulocyte production index

Haematology

Is the marrow responding to anaemia? The raw reticulocyte % misleads because reticulocytes are released early and live longer in severe anaemia.

What you enter

FORMULARPI = reticulocyte % × (Hct ÷ 45) ÷ maturation factor (Hct ≥35: 1; 25–34: 1.5; 20–24: 2; <20: 2.5)

SourceHillman RS, Finch CA. Red Cell Manual (the reticulocyte maturation correction); reviewed in Piva E et al. Clin Chem Lab Med 2010ReviewedFormula and thresholds checked against the source on 2026-08-22. If the source updates, this line will say so.