Features:
(1) presentation with apparent mild macrocytic anemia and polychromasia (due to reticulocytosis)
(2) hemolysis during running or hiking, followed by hemoglobinuria, decreased haptoglobin levels, and schistocytes in the peripheral blood smear
(3) expansion of plasma volume, with dilution of a normal red cell mass ("pseudoanemia") and other cellular elements (pseudopancytopenia)
(4) disappearance of the anemia on temporary discontinuation of exercise for several weeks
Long distance runners may also develop a concomitant blood loss from the gastrointestinal tract.
The hemolysis occurs during the foot strike with each step. Older red cells have more rigid membranes and are more susceptible to rupture during the exercise.
Factors affecting the severity of hemolysis:
(1) total distance traveled
(2) running or hiking surface
(3) footwear
(4) load carried
The differential diagnosis is large, and includes:
(1) menstrual blood loss in women
(2) nutritional deficiencies
(3) drug toxicity
(4) myelodysplasia
(5) alcohol abuse
(6) paroxysmal nocturnal hemoglobinuria (PNH)
