A 32 year old high altitude rock climber is observed to have a hematocrit of 70 percent. Which of the following represents the MOST likely explanation?

Mountaineers at high altitude develop physiological increase in erythropoietin levels due to decreased aerial oxygen saturation. This leads to absolute Polycythemia with increased red cell mass. 'Red cell mass' is the investigation of choice to establish the diagnosis. Once 'red cell mass' determination confirms absolute erythrocytosis, a diagnosis of high altitude associated secondary Polycythemia can be established by demonstrating elevation in serum erythropoetin levels. Ref: Review of Medical Physiology by William ganong, 22nd edn/page 686.