What does low osmotic fragility means?

Answer 1

Osmotic fragility usually (unless otherwise mentioned) refers to the ease with which Red Blood Cells (RBCs) undergo lysis in a hypotonic solution.

Before knowing what 'low osmotic fragility' means, one should know the concept of osmotic fragility. Different parameters, some of them related to the RBC and some of the extracellular environment have an effect on osmotic fragility.

Low osmotic fragility means that the RBCs have a resistance against undergoing lysis when suspended in solutions which are hypotonic. They undergo lysis only if the solution is extremely hypotonic.

In contrast, high osmotic fragility refers to the tendency of the RBCs to lyse even if the solution in which they are suspended in is mildly hypotonic.

As an example for low osmotic fragility would be thalassemia.

And as an example for high osmotic fragility, spherocytosis (a hereditary condition where the RBCs lose their usual biconcave structure and become spherical) causes increased osmotic fragility. i.e, It very easily lyses even at solutions which are mildly hypotonic...

p.s

Another interesting point to note is that in sickle cell anemia, the RBCs show increased mechanical fragility but decreased osmotic fragility. Elucidated by the fact that post-splenectomy the RBC lifespan increases.