<prompt> A 32 year old high altitude mountaineer is observed to have a hematocrit of 70. Which of the following represents the most likely causeexplanationPolycythemia with increased red cell massRelative polycythemia due to dehydrationPolycythemia due to hemoconcentrationPolycythemia with high altitude pulmonary edema  <response>: Erythropoietin secretion increases promptly on ascent to high altitude. The increase in circulating red blood cells triggered by the erythropoietin begins in 2-3 days and is sustained as long as the individual remains at high altitude. 