Osmotic Fragility of Red Blood Cells (RBCs)

Aim: To determine osmotic fragility of Red Blood Cells (RBCs) of own blood sample. 

Requirements:  Disposable needle 26G, suitable antiseptic solution, glass slide, and coverslips, dropper, sodium chloride solution, and distilled water. 

Principle:  The mixing of blood with different concentrations of NaCl solution is a widely used method. The osmotic fragility of RBCs is the degree of hemolysis that takes place when RBCs are mixed with hypertonic solution giving osmotic stress to the cells. On average, 50% of RBCs are ruptured at the fragility point i.e. about 0.5-0.6% of NaCl. Generally, the hemolysis begins at 0.68% NaCl and is completed at 0.33% NaCl. 


1. Label the test tubes from 1 to 12 numbers and place them on test tube stands. 

2. Carefully add the calculated number of drops of distilled water and 1% NaCl solution in test tubes as shown in the table.


Osmotic Fragility of Red Blood Cells (RBCs)

3. Sterilize the tip of the ring finger with the 70% alcohol or suitable antiseptic solution and gently prick the finger. 

4. Add a drop of blood to each test tube and shake well (approximately for 2-3 minutes) to ensure uniform mixing and then keep it undisturbed for the next 30 minutes. 

5. After 30 minutes, observe the supernatant fluid and sediments of the RBCs beginning from highest to lowest concentration. 

6. Appearance of slightly red supernatant fluid along with some sediment at the bottom indicates the beginning of hemolysis and the presence of clear supernatant liquid indicates the completion of hemolysis. 

7. The range from starting to completion of hemolysis is considered the fragility of RBCs.

Normal range: 0.68-0.33%. 

Result: The osmotic fragility of RBC of own blood sample was found to be …… 

Clinical Significance:

Clinical Significance
Make sure you also check our other amazing Article on : White Blood Corpuscles Count
Sharing Is Caring:

Leave a Comment