Hemoglobin Osler: report of a new family with exercise studies before and after phlebotomy.

Five members of a new family with hemoglobin Osler are described. Exercise studies were performed before and after phlebotomy in one patient. These studies demonstrated that anaerobic threshold was directly related to hematocrit. Our data suggest that the elevation of red cell mass seen with this high oxygen affinity hemoglobin is an appropriate physiologic response which improves tissue oxygen delivery. Despite the increase in whole blood viscosity associated with erythrocytosis, our data do not support the use of therapeutic phlebotomy to improve exercise performance in patients with hemoglobin Osler.