Osmotic Fragility Test
Osmotic fragility measures red blood cell (RBC) resistance to hemolysis when exposed to a series of increasingly dilute saline solutions. The sooner hemolysis occurs, the greater the osmotic fragility of the cells.
Procedure and posttest care
Osmotic fragility values (percentage of RBCs hemolyzed) are determined by the tonicity of the saline. Reference values for the different tonicities are as follows:0.5 g/dl sodium chloride (NaCI) solution (unincubated)
0.6 g/dl NaCI solution (incubated)
0.65 g/dl NaCI solution (incubated)
0.75 g/dl NaCI solution (incubated)
Low osmotic fragility (increased resistance to hemolysis) is characteristic of thalassemia, iron deficiency anemia, sickle cell anemia, and other red cell disorders in which codocytes (target cells) and leptocytes are found. Low osmotic fragility also occurs after splenectomy.
High osmotic fragility (increased tendency to hemolysis) occurs in hereditary spherocytosis, in spherocytosis associated with autoinunune hemolytic anemia, severe burns, or chemical poisoning, or in hemolytic disease of the newborn (erythroblastosis fetalis).
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