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Reticulocyte Production Index

RPI · Corrected reticulocyte count · Hypoproliferative vs hyperproliferative anemia

Enter Lab Values

Reticulocyte Count

Normal: 0.5–2.5%. Absolute normal: 25–105 ×10³/µL.

Hematocrit (Hct)

Normal M: 41–53% F: 36–46%

Hemoglobin (optional — used to confirm anemia)

g/dL

Normal M: 13.5–17.5 F: 12.0–15.5 g/dL

MCV (optional — for context)

Normal: 80–100 fL

The maturation factor (shift factor) is automatically selected based on the patient's hematocrit: 1.0 at Hct ≥ 35%, 1.5 at 25–34%, 2.0 at 20–24%, and 2.5 at < 20%. This corrects for early release of reticulocytes into circulation under erythropoietic stress.

RPI Interpretation & Formulas

RPI	Marrow Response	Anemia Type	Common Causes
< 2	Hypoproliferative	Inadequate marrow response	Iron deficiency · B12/folate deficiency · ACD · CKD · Aplastic anemia · Marrow infiltration · Hypothyroidism
2–3	Borderline	Marginally compensated	Early recovery from deficiency · Mixed picture · Partially treated anemia
≥ 3	Hyperproliferative	Appropriate marrow response	Acute blood loss · Hemolytic anemia (autoimmune, sickle cell, G6PD, TTP) · Post-treatment response

Step 1 Corrected Reticulocyte % = Retic% × (Patient Hct ÷ Normal Hct)

Step 2 RPI = Corrected Retic% ÷ Maturation Factor

Maturation Hct ≥ 35% → 1.0 | 25–34% → 1.5 | 20–24% → 2.0 | < 20% → 2.5

Normal Hct reference: Male = 45%, Female = 41%. Source: Hillman RS. Reticulocyte production index. Hematology 2001; Tefferi A, Mayo Clinic Hematology Manual.