Why dilution factor is 1: 20 in WBC count

Reading File

Finding Sources

Reading File

Searching the Web

why 1:20 dilution factor WBC count Turk's fluid hemocytometer

Here is a thorough explanation of why a 1:20 dilution is used for the manual WBC count:

Why 1:20 Dilution in WBC Count?

1. WBCs Are Far Less Numerous Than RBCs

The key reason is the relative abundance of cells in blood:

Cell Type	Normal Count	Dilution Used
RBC	4.5 - 5.5 million/µL	1:200
WBC	4,000 - 11,000/µL	1:20

WBCs are approximately 1000 times fewer than RBCs. If you used the same 1:200 dilution as for RBCs, the WBCs would be too sparse to count reliably in the Neubauer counting chamber. A lighter dilution of 1:20 brings the WBC concentration into a countable range (neither too crowded nor too sparse).

2. RBCs Must Be Eliminated

In whole blood, RBCs vastly outnumber WBCs and would obscure them completely. Turk's fluid (the diluting fluid) contains glacial acetic acid (1-2%), which:

Lyses (destroys) all RBCs so they don't interfere
Leaves WBCs intact

This means you only need enough dilution to make WBCs countable - you don't need the heavy dilution required for RBC counting.

3. Composition of Turk's Fluid

Component	Amount	Role
Glacial acetic acid	1-2 mL	Lyses RBCs
Gentian violet	1 mL of 1% solution	Stains WBC nuclei (faint blue-violet tint) for easier identification
Distilled water	up to 100 mL	Diluent

4. How the 1:20 Dilution Is Achieved Practically

Using a WBC pipette (Thoma pipette):

Draw blood up to the 0.5 mark
Draw Turk's fluid up to the 11 mark
Volume of blood = 0.5 units
Total volume = 11 units
Dilution = 0.5/11 ≈ 1:20 (technically 1:21, but conventionally stated as 1:20)

Alternatively, mix 2 µL of blood with 38 µL of Turk's fluid = 1:20 dilution.

5. The Counting Formula

After loading the Neubauer chamber, WBCs are counted in all 4 large corner squares:

WBC/µL = (Cells counted × Dilution factor × Depth factor) / Area counted = N × 20 × 10 / 4 mm² = N × 50

The dilution factor of 20 is directly plugged into this formula.

6. Why Not 1:10 or 1:100?

1:10 - Too concentrated; cells overlap and are difficult to count individually
1:100 - Too dilute; too few cells per field, increasing counting error (Poisson error)
1:20 - The "sweet spot" that gives approximately 20-100 cells per large square, the optimal counting density

In summary: The 1:20 dilution is chosen because WBCs are rare enough that only a modest dilution is needed to make them countable, the acetic acid in Turk's fluid removes all RBCs so they are no longer a source of interference, and this dilution yields a cell density that minimizes both overcrowding and counting error on the Neubauer hemocytometer.

Normal value of hemoglobin and rbc in male and female

Finding Sources

Reading File

Finding Sources

Here are the normal reference values for Hemoglobin and RBC count in males and females, directly from authoritative textbooks:

Normal Hemoglobin Values

Gender	Conventional	SI Units
Male	13.5 - 17.5 g/dL	135 - 175 g/L
Female	12.0 - 16.0 g/dL	120 - 160 g/L

Males have higher hemoglobin because testosterone stimulates erythropoiesis and increases RBC production. Females have lower values partly due to menstrual blood loss and lower androgen levels.

Normal RBC Count

Gender	Conventional	SI Units
Male	4.3 - 5.7 × 10⁶ cells/µL	4.3 - 5.7 × 10¹²/L
Female	3.8 - 5.1 × 10⁶ cells/µL	3.8 - 5.1 × 10¹²/L

Normal Hematocrit (for context)

Gender	Value
Male	39 - 49%
Female	35 - 45%

Hematocrit is approximately 3× the hemoglobin value and falls alongside Hb and RBC in anemia.

Quick Summary of Other Related Red Cell Indices

Parameter	Normal Range
MCV	80 - 100 fL
MCH	26 - 34 pg/cell
MCHC	31 - 37 g Hb/dL RBCs

Why Are Male Values Higher?

Testosterone stimulates the kidneys to produce more erythropoietin (EPO), which drives RBC production in the bone marrow
Estrogen in females mildly suppresses erythropoiesis
Menstrual blood loss in premenopausal females lowers iron stores and RBC mass
After menopause, the gap between male and female values narrows

Source: Textbook of Family Medicine, 9th Edition (eTable 14-4 - Complete Blood Count Reference Ranges)

This is a shared conversation. Sign in to Orris to start your own chat.