Final answer:
Low oxygen levels, dehydration, and high altitude increase sickling of sickle Hb.
Step-by-step explanation:
The factors that increase sickling of sickle Hb are low oxygen levels, dehydration, and high altitude. When oxygen levels are low, the shape of the red blood cell changes to become crescent-shaped, reducing its ability to deliver oxygen. Dehydration and high altitude can also cause the red blood cells to sickle, further impairing oxygen delivery.