The first cause of hyperhemoglobinemia is smoking, living at high altitude or both.

Smoking decreases the oxygen-carrying capacity of the red blood cells. This causes the body to create more red blood cells to provide the oxygen that the body needs. Now, whether you smoke or not, those living at high altitudes can also find themselves with high levels of hemoglobin, as the body creates more red blood cells to make-up for a limited oxygen supply in the air. Your agency may use adjusted cut-off values based upon smoking, living at high altitudes or both.