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diabetics.
b) Type 2
MacLeod et al. (1993) studied the frequency of severe hypoglycaemia in 600 randomly selected patients
with insulin-treated diabetes attending a large diabetic outpatient clinic. 175 (29.2 per cent) of the 600
patients reported a total 964 episodes of severe hypoglycaemia in the preceding year, giving an overall
frequency in the group of 1.6 episodes per patient per year. The frequency of severe hypoglycaemia in
Type 1 diabetics was more than double that in Type 2 diabetics being treated with insulin (1.7 vs. 0.73
episodes per patient per year).
This differing rate of hypoglycaemia has been confirmed by Heller et al (2007) who found no differences
in the rate of severe hypoglycaemia in Type 2 diabetic patients treated with sulphonylureas or insulin for
less than two years (0.1 and 0.2 episodes per subject-year) and this frequency is far less than that
encountered in Type 1 diabetes (< 5 years 1.1; > 15 years 3.2 episodes per subject-year).
This finding of a lower average rate of hypoglycaemia in Type 2 diabetes was noted by Wright et al.
(2002) in the United Kingdom Prospective Diabetes Study (UKPDS) who found that the rate of severe
hypoglycaemia in Type 2 diabetics treated with insulin alone was 3.2 per cent per annum -while 1.6 per
cent per annum in those who were treated with clorpropramide or glycazide with or without insulin.
Cryer (2002) in a review of the literature also suggested that the risk of serious hypoglycaemia is much
less in Type 2 diabetes, even in patients treated intensively as judged by HbA1c levels.
3. Estimation of incapacitation risk
Based on the data from this literature review, the rate of severe hypoglycaemia, i.e. hypoglycaemia
requiring the help of another, in Type 2 diabetics treated with insulin is 3.2 per cent per annum. These
ICAO Preliminary Unedited Version — March 2010 III-4A-4
data, however, come from hospital populations; the pilot group are highly selected, well motivated and
usually meticulous in managing their diabetes. If only those Type 2 diabetics are selected who have a low
risk of hypoglycaemia, the figure is likely to be less. Using this extrapolation, one may estimate the
annual rate to be between one and two per cent.
4. Risk of subtle impairment of performance
Data to estimate this prevalence are rather difficult to obtain and frequently not robust, but from the study
of Pramming (1991), one may postulate, using the work of McLeod (1993), that the rate of mild
hypoglycaemia may be 50 per cent less in Type 2 diabetics than Type 1. Wright et al (2006) categorised
hypoglycaemic episodes in patients with Type 2 diabetes maintained on monotherapy with diet,
sulphonylurea, metformin or insulin and the proportions of patients reporting at least one episode per year
were calculated in relation to therapy. Only 2.5 per cent per year reported substantive hypoglycaemia and
only 0.55 per cent reported major hypoglycaemia. Cull et al (2001) reported hypoglycaemia rates in
those treated with basal insulin of 3.2 per 100 patient years.
The lower rate of hypoglycaemia in Type 2 diabetes has been confirmed by Holman et al (2009) in the
“4-T” Study. This differing rate of hypoglycaemia between Type 1 and Type 2 diabetes may be due in
part to the preservation of the glucose counter regulation mechanism which protects against progression
to severe hypoglycaemia. In contrast to Type 1 diabetes, the rate of substantive hypoglycaemia in Type 2
diabetes is lower, ranging from 2.5 to 3.2% per annum. As mentioned, these data are from hospital
populations and in the pilot population, highly committed and well educated in diabetes, it is likely, using
careful selection criteria, that the rate may be lower.
5. Selection criteria
On the basis of the literature review it would be appropriate to consider only Type 2 insulin-treated
diabetes with its lower prevalence of hypoglycaemia. For Class 1 applicants, certification should be
limited to multicrew operations.
The following selection criteria are based on criteria used by one Contracting State:
• No hypoglycaemic episodes requiring the intervention of another party during the previous
12 months
• Stability of blood glucose control in the year prior to certification as measured by
glycosylated (glycated) haemoglobin which should be less than twice the upper limit of
normal for the laboratory assay. 90 per cent of blood glucose levels should be greater than 5.5
mmol/L. The individual should have good diabetic education and be well motivated to
achieve good control. There should be no evidence of hypoglycaemic unawareness and the
individual should fall into the “low risk group of hypoglycaemia” shown in Table 1. In
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Manual of Civil Aviation Medicine 1(137)
