I am a regular blood donor and I am also a skydiver. We normally go to around 13,000 feet AGL (above ground level). Depending on how high above sea level the ground is, altitudes could be as high as 15,000 MSL (mean sea level) before a jumper is required to use supplemental oxygen.
At those altitudes hemoglobin is less effective at carrying oxygen, which is why hypoxia is a risk.
The following chart taken from this article about aviation and the body shows how oxygen levels decrease as altitude increases:
What I would like to know is if there is any research into the effect blood donation has on the blood stream's oxygen capacity? Is it possible to say that x days after a donation, due to reduced hemoglobin levels, operating at 15,000 MSL would be equivalent to operating at 15,000 + x MSL without donation?