Stomatocytosis is a rare condition of RBCs in which a mouthlike or slitlike pattern replaces the normal central zone of pallor. Stomatocytosis can be congenital or acquired; both may be asymptomatic or result in hemolysis. Symptoms, if present, result mainly from the anemia.

Congenital stomatocytosis, which shows autosomal dominant inheritance, is rare. It can cause a severe hemolytic anemia presenting very early in life. The RBC membrane is hyperpermeable to monovalent cations (sodium and potassium); movement of divalent cations and anions is normal. The percentage of stomatocytes varies RBC fragility is increased, as is autohemolysis with inconstant correction with glucose. Splenectomy ameliorates anemia in some cases.

Acquired stomatocytosis with hemolytic anemia occurs primarily with recent excessive alcohol ingestion. Stomatocytes in the peripheral blood and hemolysis disappear within 2 wk of alcohol withdrawal.

RBC pliability varies according to intracellular ATP levels. Because the serum phosphate concentration affects RBC ATP levels, low serum phosphate level (< 0.5 mg/dL [< 0.16 mmol/L]) depletes ATP levels in RBCs. The complex metabolic sequelae of hypophosphatemia also include 2,3-diphosphoglyceric acid depletion, a shift to the left in the oxygen dissociation curve, decreased glucose utilization, and increased lactate production. The resultant rigid, nonyielding RBCs are susceptible to injury in the capillary circulatory bed, leading to hemolysis and small, sphere-shaped RBCs (microspherocytosis).

Severe hypophosphatemia may occur in

Phosphate supplements prevent or reverse the anemia and are considered for patients at risk of or who have hypophosphatemia.