Decreased osmotic fragility is seen in:

 # Which of the following have decreased osmotic fragility? 

a. Hereditary spherocytosis 

b. Hereditary elliptocytosis 

c. Hereditary xerocytosis 

d. Hereditary stomatocytosis/hydrocytosis

The correct answer is C. Hereditary xerocytosis.

Osmotic fragility has been typically increased in Hereditary spherocytosis and hereditary  elliptocytosis. There are 2 types of hereditary stomatocytosis: hereditary xerocytosis (complex permeability defect d/t increased membrane lipids) and hereditary stomatocytosis – hydrocytosis (d/t deficiency of band 7.2b or stomatin). Both have autosomal dominant inheritance. Osmotic fragility is decreased in xerocytosis and increased in hydrocytosis. Xerocytosis may result in recurrent fetal loss, hydrops fetalis, neonatal hepatitis and familial pseudohyperkalemia.

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