High prevalence of increased osmotic fragility of red blood cells among Norwegian blood donors.

Increased osmotic fragility of red blood cells was found in 9 out of 1008 Norwegian blood donors. In addition, increased osmotic fragility was found in 3 out of 23 first grade relatives and in 1 out of 4 spouses of individuals with the same condition. Finally, there was a positive correlation between increased osmotic fragility and morphological signs of spherocytosis (P less than 0.05). No definite conclusions with respect to underlying mechanism(s) for this high prevalence of non-symptomatic increased osmotic fragility can be offered, but very mild hereditary spherocytosis, environmental factors and even a normal variant, never associated with haemolysis, may have contributed. Furthermore, until more specific and sensitive laboratory techniques have been introduced, a proper distinction between these 3 conditions cannot be made.