Anemia (and fitness to fly)

• Sickle cell trait does not present a particular problem at normal cruising altitude. However, patients with sickle cell anaemia should travel with supplemental oxygen and should defer travel for approximately 10 days following a sickling crisis (1)
• patients with a haemoglobin of greater than 8 g/dl may travel without problems assuming there is no coexisting condition such as cardiovascular or respiratory disease (1)
  
  
• if the haemoglobin is less than 7.5 g/dl, special assessment should be made and the use of supplemental oxygen should be considered (1)

Note guidance varies between sources (2,3):

• anaemia - may require in flight oxygen. A haemoglobin below 8.5 g/dl requires special consideration before permitting to fly (2,3).
  • a haemoglobin below 7.5 g/dl is generally a contraindication to air travel (3)
    
    
• individuals with chronic renal insufficiency or other medical condition predisposing to anaemia, which is chronic in nature, will usually tolerate a lower haemoglobin level than if the anaemia is of acute onset.

Note that these are only guidelines - each airline has its own regulations and medical standards and these must be consulted before travel

Reference:

• Civil Aviation Authority. Fitness to Fly (Accessed 1/8/19)
• International Air Transport Association. Medical Manual 11th Edition (2018).
• 'Medical guidelines for air travel', Aviation, Space and Environmental Medicine, October 1996, 67, 10, 11