What Is Total Leucocyte Count (TLC) meaning, Procedure, normal value, clinical significance.

 

Total Leucocyte Count (TLC): Procedure, Calculation, and Clinical Significance

Introduction

Total Leucocyte Count (TLC) refers to the total number of white blood cells (WBCs) present in 1 microliter (µL) of blood.

WBCs are crucial components of the immune system, responsible for defending the body against infections, foreign substances, and abnormal cells.

Table of content

1. Introduction
2. Normal TLC range in adults
3. Required Equipment for TLC Estimation
4. Reagents Used
5. Method for Estimating Total Leucocyte Count
6. Calculation of TLC
7. Clinical Applications and Interpretation
8. Common Clinical Uses:
9. Precautions
10. Conclusion

Normal TLC range in adults: 4,000 – 11,000 WBCs/µL of blood

Abnormal TLC can indicate infections, inflammations, immune system disorders, or bone marrow abnormalities.

Required Equipment for TLC Estimation

1. Neubauer’s Hemocytometer (Improved Neubauer chamber)

2. WBC pipette

3. Turk’s fluid (Diluting fluid containing glacial acetic acid and gentian violet stain)

4. Microscope

5. Lancet or sterile needle

6. Alcohol swab

7. Blood collecting materials (capillary tube or syringe)

8. Clean glass slides and cover slips

Reagents Used

Turk’s fluid Composition:

Glacial acetic acid – lyses red cells

Gentian violet – stains the nuclei of WBCs

Distilled water – solvent

Method for Estimating Total Leucocyte Count

1. Blood Sample Collection:

Collect capillary blood from a finger prick or venous blood in an EDTA tube.

2. Dilution:

Draw blood up to the 0.5 mark of the WBC pipette.

Draw Turk’s fluid up to the 11 mark to achieve a 1:20 dilution.

3. Mixing:

Mix the blood and Turk’s fluid thoroughly by rotating the pipette for 1-2 minutes.

4. Charging the Hemocytometer:

Discard the first few drops of the mixture.

Fill the Neubauer counting chamber using a capillary action method under a cover slip.

Allow the cells to settle for 2–3 minutes.

5. Counting:

Under the microscope (10x objective), count WBCs in the four large corner squares of the Neubauer chamber.

Calculation of TLC

Formula:

TLC (cells/µL) = (Number of cells counted x dilution factor)/Volume of area counted

Example

Suppose total cells counted = 50

Dilution = 20

Volume = 4 large squares × 0.1 mm depth × 1 mm² each = 0.4 mm³ = 0.4 µL

TLC= (50 x 20)/0.4 = 2500 cells/µL

Clinical Applications and Interpretation

TLC Value	Interpretation Possible Causes
< 4,000/µL	Leucopenia (Low WBC count)            Viral infections, bone marrow suppression, autoimmune diseases
4,000–11,000/µL	Normal Range  Normal immunity
> 11,000/µL	Leucocytosis (High WBC count)         Bacterial infections, inflammation, leukemia, stress

 

Common Clinical Uses:

Diagnosing infections (bacterial vs viral)

Monitoring bone marrow function

Evaluating immune status in chronic illness

Part of routine blood tests (CBC)

Precautions

Ensure accurate dilution to avoid miscalculation.

Avoid air bubbles in the hemocytometer.

Count only well-defined WBCs (nucleated cells).

Disinfect instruments properly after use.

Conclusion

Total Leucocyte Count is a fundamental and cost-effective diagnostic tool in medical practice. It provides essential insights into the body's immune status and plays a vital role in diagnosing infections, inflammations, and hematological disorders. Mastery of its manual method is crucial for laboratory technicians and medical professionals, even in the era of automated counters.