Hematology Practical Quiz: Osmotic Fragility Test Questions

Study Notes

Erythrocyte Surface Area and Volume Ratio

Decreased surface-to-volume (S/V) ratio leads to increased osmotic fragility (OF)
Increased S/V ratio leads to decreased OF

Osmotic Fragility Test

Performed to detect hereditary spherocytosis, a disorder characterized by defective red blood cells with a spherical shape and decreased S/V ratio
These cells are more fragile and less likely to expand

Normal Range of Fragility

Hemolysis begins in approximately 0.45% saline
Hemolysis is complete at 0.3% NaCl
No cells hemolyze in solutions of 0.5% saline and above

Hereditary Spherocytosis (HS) Blood Picture

Peripheral blood smear shows multiple spherocytes, small, dense red cells without central pallor
Findings can be seen in HS or autoimmune hemolytic anemia

Principle of Osmotic Fragility Test

Normal red cells can remain suspended in normal saline (0.9% NaCl solution) for hours without rupturing or changing in size or shape
When placed in decreasing strengths of hypotonic saline, they absorb water and finally burst

Method of Osmotic Fragility Test

Heparinized venous blood is used
Test determines the ability of RBCs to resist hemolysis quantitatively

Osmosis and Erythrocyte Fragility

Osmosis: spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration
Erythrocyte fragility: tendency of erythrocytes to hemolyse under stress (commonly osmosis)

Solutions and Their Effects

Isotonic solution: same salt concentration as cells and blood, no net movement of water
Hypertonic solution: higher concentration of solute particles, causing water to flow out of the cell and shrink
Hypotonic solution: lower concentration of solute particles, causing water to flow into the cell

Factors Affecting Osmotic Fragility

Shape of the RBC, dependent on:
- Cell membrane permeability
- Surface-to-volume ratio

Description

Test your knowledge on the osmotic fragility test for erythrocytes in this practical session quiz. Understand the concept of osmosis and the tendency of red blood cells to hemolyse. Prepared for fourth-year students on February 1, 2024, by Dr. Salar Ayob Sulaiman.