Osmotic fragility test of red blood cells

The osmotic resistance of erythrocytes is determined primarily by the primarily the volume to surface area ratio of the blood cell. The environment hypotonic causes an increase in erythrocyte volume, due to the penetration of water into the blood cell.

The causes of reduced osmotic resistance are:

• spherocytosis congenital, 
• some acquired anemias hemolytic with associated spherocytosis, 

The causes of increased osmotic resistance are:

• thalassemia, 
• sickle cell anemia sickle cell, 
• splenectomy (removal of the spleen).