Reticulocytes are young red cells. In anaemia, a healthy marrow increases production: an RPI above 2–3 suggests blood loss or haemolysis, while an RPI below 2 suggests underproduction (iron, B12 or folate deficiency, kidney disease or marrow failure).
How to use the Reticulocyte Count Calculator
- Reticulocytes
- Haematocrit
- Red blood cell count
- Normal haematocrit
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the reticulocyte percentage, haematocrit and red cell count from your blood test.
Inputs explained
| Field | What to enter |
|---|---|
| Reticulocytes | In % |
| Haematocrit | In % |
| Red blood cell count | In ×10¹²/L |
| Normal haematocrit | In % |
What each result means
- Absolute reticulocyte count = [Red blood cell count]×[Reticulocytes]÷100×1000
- Corrected reticulocyte % = [Reticulocytes]×[Haematocrit]÷[Normal haematocrit]
- Reticulocyte production index = [Corrected reticulocyte %]÷[Maturation factor]
Example values
How the main result changes when Reticulocytes changes and everything else stays at the example values above:
| Reticulocytes (%) | Reticulocyte production index |
|---|---|
| 1.5 | 0.5 |
| 2.25 | 0.75 |
| 3 | 1 |
| 3.75 | 1.25 |
| 4.5 | 1.5 |
| 6 | 2 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Absolute reticulocytes = RBC × retic % ÷ 100
Corrected retic % = retic % × Hct ÷ 45
RPI = corrected retic % ÷ maturation factor (1.0 for Hct ≥ 40%, 1.5 for 35–39, 2.0 for 25–34, 2.5 for 15–24, 3.0 for < 15)
Worked example
Inputs — Reticulocytes: 3 %; Haematocrit: 30 %; Red blood cell count: 3.5 ×10¹²/L; Normal haematocrit: 45 %.
Results — Absolute reticulocyte count = 105 ×10⁹/L; Corrected reticulocyte % = 2 %; Maturation factor = 2; Reticulocyte production index = 1.
Key terms
- RPI
- Reticulocyte production index.
Frequently asked questions
What is a normal reticulocyte count?
About 0.5–2.5% (25–100 ×10⁹/L).
Why correct for haematocrit?
In anaemia there are fewer red cells, which inflates the percentage of reticulocytes.
Why use the RPI?
It also accounts for reticulocytes released early from the marrow and staying longer in the blood.