Hemoglobin San Diego: An Uncommon Cause of Hereditary Erythrocytosis Discovered Incidentally in a Military Trainee.

High-affinity hemoglobinopathies are a rare clinical entity that commonly presents as an isolated erythrocytosis in asymptomatic individuals. We report such a case involving an 18-year-old active duty military trainee who presented to the hematology clinic after an isolated erythrocytosis was incidentally discovered during a flight physical. The patient was asymptomatic but did report a family history of erythrocytosis in his mother and maternal grandmother which intermittently required venesection. Initial history and physical exam were unremarkable. P50 RBC Oxygen Dissociation showed a left-shifted oxygen dissociation curve, although hemoglobin electrophoresis did not reveal an abnormal hemoglobin variant. A β-globin variant was identified via mass spectrometry and sequencing that was consistent with the rare high-oxygen affinity hemoglobin variant designated hemoglobin San Diego. This patient was medically cleared to return to training without limitations and counseled regarding the potential significance of being a carrier of this rare hemoglobin variant. This case represents the first observation of hemoglobin San Diego in the U.S. military population. Published by Oxford University Press on behalf of the Association of Military Surgeons of the United States 2018.