This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
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 
Select and explain. 
A. Polycythemia with increased red cell mass, B. Relative Polycythemia due to dehydration, C. Polycythemia due to hemoconcentration, D. Polycythemia with high altitude pulmonary edema
A: Polycythemia with increased red cell mass
Answer: A: Polycythemia with increased red cell mass 
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