Hereditary Spherocytosis

Hereditary spherocytosis (HS) is an inherited red-cell membrane disorder in which membrane surface is gradually lost. The cell becomes spherical and less deformable, so the spleen removes it prematurely. This produces chronic extravascular haemolysis, but the haemoglobin may remain normal when the marrow compensates with increased reticulocyte production. For the nurse practitioner, the high-value pattern is spherocytes plus evidence of haemolysis and a negative direct antiglobulin test. The finding that changes urgency is not simply a falling haemoglobin: it is a falling haemoglobin with an inappropriately low reticulocyte count, which suggests parvovirus B19–associated aplastic crisis. A second major shift in risk occurs after hyposplenism or splenectomy, when fever becomes a medical emergency because overwhelming infection can progress within hours.