A 32-year-old high altitude mountaineer is observed to have a hematocrit of 70 percent. Which of the following represents the most likely cause/explanation
At high altitude, there can be acute changes and changes due to acclimatization.
Acute mountain sickness

Dyspnoea, dizziness, tiredness, tachycardia, palpitation, nausea, vomiting etc. 
At higher altitudes- pulmonary oedema and cerebral oedema may occur. 

Acclimatization changes

Hyperventilation leading to respiratory alkalosis 
Increased 2,3DPG- Hb-O2 dissociation curve shifts to right. 
Increased erythropoietin leading to absolute polycythemia with increased red cell mass. 
Increased renal excretion of bicarbonate 
Increased tissue vascularity 
Increased oxidative metabolism 
Increased diffusion capacity of the lung​
Increased myoglobin
Polycythemia with increased red cell mass
Relative Polycythemia due to dehydration
Polycythemia due to hemoconcentration
Polycythemia with high altitude pulmonary edema