When performed as part of a CASA aviation medical, fasting glucose (FG) must be under 5.5 to be considered “normal”; which is in fact below the upper limit of the labs’ reference ranges, leading to some confusion. Applicants having a value over this will be requested to undertake an oral glucose tolerance test (OGTT), when they give 3 hourly blood samples after being given a 75g glucose challenge. A similar baseline result will be considered “impaired fasting glucose”; an elevated 2 hour result is called “impaired glucose tolerance”. A diagnosis of diabetes will be a very unusual result in these cases. Thus the practical implication is a potential exercise stress test for the applicant with a calculated coronary risk score (CRI) of >14: much of this risk comes from age and male gender, though other variables are contributory. The short version: in vast majority of cases, a certificate will still be issued after much ado, but with stipulation for future followup.
In my experience, suboptimal fasting can lead to the initial abnormal result. 12 hours of fasting is the instruction given beforehand, though overfasting is also problematic. Applicants with marginal insulin resistance would be wise to choose their dinner from before carefully — indeed, all of their meals every day.
A body mass index (BMI) of 30 and above will trigger the need for FG, and therefore the above protocol. As age creeps up CRI may well exceed 14, further triggering an exercise stress test. For a pilot, weight management (through regular exercise and a balanced diet) is important.
Dr. Charles Tsang MBChB(Otago) FRNZCGP 