• L Rice, W Ruiz, T Driscoll, C E Whitley, R Tapia, D L Hachey, G F Gonzales, and C P Alfrey.
• Section of Hematology, Department of Medicine, Baylor College of Medicine, 6565 Fannin, MS 902-Main, Houston, TX 77030, USA. lrice@bcm.tmc.edu
• Ann. Intern. Med. 2001 Apr 17; 134 (8): 652-6.

BackgroundStudies of space-flight anemia have uncovered a physiologic process, neocytolysis, by which young red blood cells are selectively hemolyzed, allowing rapid adaptation when red cell mass is excessive for a new environment.Objectives1) To confirm that neocytolysis occurs in another situation of acute plethora-when high-altitude dwellers with polycythemia descend to sea level; and 2) to clarify the role of erythropoietin suppression.DesignProspective observational and interventional study.SettingCerro de Pasco (4380 m) and Lima (sea level), Peru.ParticipantsNine volunteers with polycythemia.InterventionsVolunteers were transported to sea level; three received low-dose erythropoietin.MeasurementsChanges in red cell mass, hematocrit, hemoglobin concentration, reticulocyte count, ferritin level, serum erythropoietin, and enrichment of administered(13)C in heme.ResultsIn six participants, red cell mass decreased by 7% to 10% within a few days of descent; this decrease was mirrored by a rapid increase in serum ferritin level. Reticulocyte production did not decrease, a finding that establishes a hemolytic mechanism.(13)C changes in circulating heme were consistent with hemolysis of young cells. Erythropoietin was suppressed, and administration of exogenous erythropoietin prevented the changes in red cell mass, serum ferritin level, and(13)C-heme.ConclusionsNeocytolysis and the role of erythropoietin are confirmed in persons with polycythemia who descend from high altitude. This may have implications that extend beyond space and altitude medicine to renal disease and other situations of erythropoietin suppression, hemolysis, and polycythemia.

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