Reticulocyte Count: Anemia Assessment and Erythropoiesis Monitoring
Synonyms
Retic Count
Specimen
Whole blood
Container
- Lavender top (EDTA) tube
- Green top (heparin) tube for venipuncture
- Heparinized capillary tube for capillary samples
Storage Instructions
EDTA-anticoagulated blood can be stored at room temperature for up to 48 hours.
Reason to Reject Sample
- Clotted specimen
- Hemolyzed specimen
Reference Range
- Adults: 0.5% to 1.5%
- Newborns: <7%
- Birth: 2.5% to 6.5%, falling to adult levels by end of week 2
- Elderly (>70 years): Slightly higher but within adult range
Use
To assess erythropoiesis (red blood cell production), particularly in conditions such as:
- Hemolytic anemia
- Acute or chronic blood loss
- Response to anemia treatment
The Reticulocyte Count helps classify anemia as hyperproliferative or nonproliferative, guiding further diagnostic tests.
Limitations
- Reticulocyte counts may appear falsely low following recent blood transfusions due to dilution.
Contraindications
- Patients receiving multiple transfusions
Methodology
Vital staining methods using:
- New methylene blue (commonly used)
- Brilliant cresyl blue (alternative)
Additional Information
An increase in reticulocyte count is a cost-effective marker of increased RBC production. However, it’s important to differentiate between a true increase and an apparent one caused by reduced mature RBCs in anemia.
Key Calculations
- Absolute Reticulocyte Count = RBC count × Reticulocyte %
- Reticulocyte Index (RI) = (Patient’s Hct ÷ Normal Hct) × Reticulocyte %
- Reticulocyte Production Index (RPI) = RI ÷ Maturation time (usually 2)
The RPI corrects for early marrow release of reticulocytes in cases like hemolysis or hemorrhage. A low RPI in anemia suggests marrow production failure.
Automated methods using image recognition or flow cytometry offer better precision than manual counting.
References
- Brecher G, “New Methylene Blue as a Reticulocyte Stain,” Am J Pathol, 1949, 19:895.
- Brown BA, Hematology: Principles and Procedures, 6th ed, 1993.
- Davis BH, Bigelow NC, “Flow Cytometric Reticulocyte Analysis,” Ann NY Acad Sci, 1993, 677:281–92.
- Houwen B, “Reticulocyte Maturation,” Blood Cells, 1992, 18(2):167–86.
- Lee GR, “The Hemolytic Disorders,” Wintrobe’s Clinical Hematology, 9th ed, 1993, pp. 944–64.
- Jacobs et al., Laboratory Test Handbook, Lexi-Comp Inc, 1994.
