During the flight, there is the risk of inaccurate blood glucose readings and for example with accu-chek strips and glucometer, it is up to 3094 meters, if you are unsure about your meter check the manual or call the manufacturer and be sure to ask!
Update: & My Sincere Thanks to
@Tipetoo bringing it to my attention and for the kind correction.
Much appreciated
As Tipetoo says; "That "3094 meters" is for external readings half way up a mountain, not in a pressurised aircraft cabin." - is perfecty true and correct.
Most manufacturers of blood glucose monitoring equipment do not give advice regarding the use of their meters and strips onboard aircraft and do not write anything about it in their manuals.
The cabin altitude in modern jet aircraft is between 6000 and 8000 ft which should not affect the accuracy of most, if not all, blood glucose meters.
Airplane flight results in exposure to hypobaric conditions. At cruising altitude, usually 10,000 to 13,000 meters (∼30,000 to 42,000 feet), the pressure in the cabin is 0.75 atm, which is 75% of the pressure measured at sea level.
The partial pressure of oxygen in the airplane cabin is 16 kPa compared to 21 kPa at sea level, thus there is a risk that a glucometer can show a false hypo- or normoglycemia while in the air, when the true value in fact could be higher.
Some airlines have blood glucose testing equipment in the aircraft cabin medical bag.