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may result in profound dehydration, raised blood sugar and ketoacidosis. This severe metabolic upset is a
relatively rare presentation and is characteristic in the young individual with Type 1 diabetes who is truly
insulin-dependent. In middle aged aircrew mild diabetes is often asymptomatic and detected at routine
medical examination by the presence of glycosuria. In the older group diabetes may present with a
vascular disorder or visual problems.
Diagnosis
The diagnosis of diabetes mellitus requires a demonstration of abnormal carbohydrate metabolism with
the exclusion of other causes for this disturbance. The other causes which may disturb carbohydrate
metabolism include hepatic disease, starvation and malnutrition, potassium depletion and other endocrine
diseases previously described such as acromegaly, Cushing’s syndrome and thyrotoxicosis.
The diagnosis, as in any clinical condition, depends on an adequate clinical history and evaluation of the
symptoms and physical findings supported by laboratory examination using internationally agreed
standards.
Glycosuria
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Glycosuria alone is not a reliable index and does not correlate well with circulating levels of blood sugar
in many individuals. Some 45 per cent of the population have a low renal threshold for glucose and may
present with glycosuria with normal circulating blood glucose.
Biochemical criteria for diagnosis
In severe cases a random or a fasting blood glucose test may be diagnostic, but random blood sugar tests
often produce uncertain results and in view of the career implication for aircrew members, a glucose
tolerance test should be carried out. The criteria for diagnosis following a 75 g glucose load has been
standardised by WHO and were modified in 1999. The diagnostic levels are shown in Table 1.
Table 1
Diagnostic criteria
Condition Blood glucose level
Diabetes fasting blood glucose:
7.0 mmol/L (126 mg/dL) and above
or
2 hours after glucose load:
11.1 mmol/L (200 mg/dL) and above
Impaired glucose tolerance fasting blood glucose:
less than 7.0 mmol/L (126 mg/dL)
and
2 hours after glucose load:
7.8 mmol/L (140 mg/dL) and above
and less than 11.1 mmol/L (200 mg/dL)
Impaired fasting glucose fasting blood glucose:
6.1 mmol/L (110 mg/dL) and above and less
than 7.0 mmol/L (126 mg/dL)
and
2 hours after glucose load:
less than 7.8 mmol/L (140 mg/dL)
Modified from Definition, diagnosis and classification of diabetes mellitus and its complications.
Report of a WHO consultation (WHO, Geneva, 1999) and the International Diabetes Federation
IGT/IFG consensus statement (Unwin N, et al. International Diabetes Federation IGT/IFG
Consensus Statement. Report of an Expert Consensus Workshop 1-4 August 2001, Stoke Poges,
UK. Diabetic Medicine 2002; 19: 708-723)
Using these criteria, there are four diagnostic categories:
1. Normal
2. Impaired glucose tolerance
3. Diabetes
4. Impaired fasting glucose
The American Diabetes Association (ADA) has published new diagnostic criteria for diabetes, suggesting
the diagnosis should be made with a fasting plasma glucose of >7 mmol/L and impaired fasting glucose
should be diagnosed when the fasting plasma glucose lies between 6.1 and 6.9 mmol/L. The ADA also
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recommended abolishing the use of the oral glucose tolerance test. The WHO has retained the glucose
tolerance test but have incorporated the lower fasting glucose level suggested by ADA.
The International Expert Committee on Diabetes (2009) recommended the additional diagnostic criteria
of an HbA1c result ≥ 6.5% for diabetes. This Committee suggested that the use of the term “pre-diabetes”
may be phased out but identified the range of HbA1c levels ≥ 6.0% and < 6.5% to identify those at high
risk for developing diabetes. The “high-risk” determination is qualified by the caveat that preventative
measures can be initiated even in patients with lower HbA1c levels if other risk factors are present.
Associated manifestations
Micro and macro-angiopathy are common consequences of diabetes. Micro-angiopathy classically affects
blood vessels of the retina and the kidney. Macro-angiopathy affects the coronary circulation, and the
incidence of coronary disease in the diabetic individual is approximately three times that of the nondiabetic
population. This has obvious implications for aircrew. Neurological complications are probably
the result of long standing metabolic upset but the pathogenesis is somewhat complex.
In Type 1 diabetes the diabetic control and complications trial (DCCT) showed clearly that good diabetic
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Manual of Civil Aviation Medicine 1(130)
