The erythrocyte osmotic fragility is the resistance of erythrocytes to different concentrations of low concentration sodium chloride solutions. Erythrocytes in hypotonic sodium chloride solution, as the erythrocytes will absorb water into themselves, which eventually leads to the rupture of the erythrocytes and hemolysis. By measuring the resistance of the erythrocytes to different concentrations of sodium chloride, the osmotic fragility of the erythrocytes can be determined. In general, increased erythrocyte osmotic fragility is mainly seen in hereditary spherocytosis, warm antibody autoimmune hemolytic anemia and hereditary oval spherocytosis, where erythrocyte osmotic fragility is also increased. Decreased erythrocyte permeability fragility is mainly seen in thalassemia and iron deficiency anemia, both of which are small cell hypochromic anemias, and in some patients with cirrhosis and jaundice.