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SOP

Manual Reticulocyte Count Procedure

Standard Operating Procedure (SOP) for performing a manual reticulocyte count using supravital staining and light microscopy to assess bone marrow erythropoietic activity.

Last verified 1 month ago 4 min read Hematology Haematology Manual Haematology Microscopy Laboratory Techniques #reticulocyte-index #anemia #Haematology #Retic Count #Erythropoiesis #rbc #reticulocyte count #manual reticulocyte #new methylene blue #brilliant cresyl blue #supravital stain #miller disc #corrected reticulocyte count #absolute reticulocyte count #bone marrow
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Document Control
Version
1.0
Effective
Aug 29, 2026
Reviewed
Aug 29, 2026
Department
Hematology
Principle

Reticulocytes are immature, anucleate red blood cells that have recently been released from the bone marrow. They contain residual ribosomal RNA (rRNA) and organelles. The manual reticulocyte count utilizes a supravital staining technique (using basic dyes like New Methylene Blue or Brilliant Cresyl Blue) which penetrates the intact cell membrane of living cells. The dye precipitates the residual rRNA, forming a dark blue, reticular network, granules, or filaments visible under a light microscope. By counting the proportion of these stained cells relative to mature red blood cells, the laboratory can quantify the rate of erythropoiesis (red blood cell production).

Standard Operating Procedure: Manual Reticulocyte Count

1. Purpose and Scope

This procedure defines the step-by-step method for performing a manual reticulocyte count. It is used to evaluate bone marrow erythropoietic activity and is essential in the classification and monitoring of anemias.

2. Specimen Requirements

  • Specimen Type: Whole venous blood or capillary blood.
  • Anticoagulant: K2EDTA or K3EDTA (Lavender/Purple top tube). Capillary blood can be collected directly into the stain.
  • Volume: Minimum 1 mL for venous blood; 1-2 drops for capillary.
  • Storage/Stability: Room temperature (18-25°C). The test should be performed within 6 hours of collection. If stored at 2-8°C, it is stable for up to 24 hours, but must be brought to room temperature before testing.
  • Rejection Criteria: Clotted, hemolyzed, or mislabeled samples.

3. Safety and Precautions

  • Wear appropriate PPE (lab coat, gloves).
  • Treat all specimens as potentially infectious.
  • Never mouth pipette. Use mechanical pipettes or capillary tubes.
  • Dispose of waste and slides in biohazard/sharps containers.

4. Equipment and Reagents

  • Equipment: Light microscope with 100x oil immersion objective, clean glass slides, coverslips, incubator or water bath (optional, 37°C), Miller disc (ocular micrometer).
  • Reagents: Supravital stain: New Methylene Blue (NMB) solution OR Brilliant Cresyl Blue (BCB) solution.

5. Step-by-Step Procedure

A. Staining and Incubation

  1. Label a small test tube with the patient's identification.
  2. Pipette 2 drops (approx. 50 µL) of the supravital stain (NMB or BCB) into the tube.
  3. Add 2 drops (approx. 50 µL) of well-mixed EDTA whole blood to the stain (1:1 ratio).
  • For capillary blood: Place 1 drop of stain on a slide, add 1 drop of blood, and mix with the corner of a second slide.
  1. Mix gently and incubate at room temperature for 10-15 minutes (or at 37°C for 10 minutes).
  2. After incubation, mix the tube again and prepare a thin blood film (smear) using standard wedge technique. Allow to air dry completely. Do not fix with methanol.

B. Microscopic Examination

  1. Examine the dried smear under the microscope.
  2. First, scan under the 40x objective to find an area with good staining and evenly distributed red blood cells (RBCs).
  3. Apply a drop of immersion oil and switch to the 100x oil immersion objective.
  4. Reticulocytes will appear as mature RBCs containing dark blue/purple reticular material, granules, or filaments. Mature RBCs will appear pale greenish-blue or pinkish-grey.

C. Counting (Miller Disc Method - Recommended)

  1. Insert a Miller disc (an ocular micrometer with one large square and one small square that is 1/9th the area of the large square) into the microscope eyepiece.
  2. Count the number of reticulocytes only within the small square until you have counted at least 100 reticulocytes (or count for a set time, e.g., 2 minutes).
  3. Simultaneously, count the total number of mature RBCs within the large square in the same fields.
  4. Note: If a Miller disc is unavailable, count all reticulocytes and total RBCs in the same field until 1,000 RBCs are counted, though this is more prone to statistical error.

D. Calculations

  1. Reticulocyte Percentage (%):
  • Using Miller Disc: Retic % = [ (Reticulocytes in small square) / (RBCs in large square × 9) ] × 100
  • Without Miller Disc: Retic % = (Total Reticulocytes counted / 1000) × 100
  1. Absolute Reticulocyte Count:
  • Absolute Retic (× 10⁹/L) = Retic % × RBC Count (× 10¹²/L) × 10
  1. Corrected Reticulocyte Count (CRC):
  • CRC (%) = Retic % × [ Patient's Hematocrit (Hct) / Normal Hct (usually 0.45 for males, 0.40 for females) ]

6. Reference Ranges

  • The canonical adult reference interval is shown in the Reference Ranges panel below.
  • Newborns: 2.0% - 6.0% (decreases rapidly after birth).
  • Absolute Count: 25 - 75 × 10⁹/L.

7. Quality Control

  • Internal QC: Perform duplicate counts on 5% of patient samples. The coefficient of variation (CV) between duplicates should be < 15%.
  • Reagent QC: Check the stain daily. It should be clear and free of precipitate. Filter the stain if precipitate is present.
  • External QC: Participate in an External Quality Assessment Scheme (EQAS) for hematology.

8. Reporting Results

  • Report the Reticulocyte Percentage (%).
  • Report the Absolute Reticulocyte Count if requested or if the RBC count is available.
  • Flag and notify the physician if the count is critically high (indicating hemolysis or acute blood loss recovery) or critically low (indicating bone marrow failure).

Reference Ranges

Browse all ranges

0.5–2.5 %

Frequently Asked Questions

New Methylene Blue is a supravital stain used on unfixed blood to precipitate RNA and visualize reticulocytes. Wright's stain is a Romanowsky stain used on fixed smears; while it can show polychromasia (bluish RBCs), it does not clearly show the reticular network required for a definitive reticulocyte count.
A Miller disc is an ocular micrometer that divides the field into a large square and a small square (1/9th the area). It significantly reduces counting fatigue and statistical error by allowing the technologist to count reticulocytes in the small square and total RBCs in the large square, rather than counting 1,000 individual RBCs.
A high reticulocyte count (reticulocytosis) indicates that the bone marrow is responding appropriately to peripheral red blood cell loss or destruction, such as in acute hemorrhage or hemolytic anemia.
The CRC adjusts the reticulocyte percentage for the patient's degree of anemia. Because the percentage is relative to the total RBC count, a low RBC count artificially inflates the reticulocyte percentage. The CRC provides a more accurate reflection of marrow output.
For optimal accuracy, the test should be performed within 6 hours of collection at room temperature. If refrigerated (2-8°C), the sample is stable for up to 24 hours, but must be returned to room temperature and mixed thoroughly before testing.