Tayside Diabetes MCN Handbook - Diagnosis of Diabetes

The Role of the Oral Glucose Tolerance Test (OGTT)

Diagnosis of Diabetes

CONSIDER a diagnosis of diabetes in a patient with:

thirst and polyuria
unexplained weight loss or tiredness
pruritus vulvae, balanitis or recurrent 'UTI's'
recurrent infections
blurring of vision (usually an osmotic effect and not permanent)
discoloured or ulcerated feet
hypertension, ischaemic heart disease or stroke
obesity, with diagnosis of arterial disease or family history of diabetes.

In such patients, it is useful to perform preliminary screening investigations i.e. random plasma glucose measurement and urinalysis for presence of glucose and ketones. The diagnosis of diabetes has important medical and legal implications for the patient.

Therefore a diagnosis of diabetes should not be based solely on finding:

glycosuria
raised capillary blood glucose (finger prick sample)
elevated haemoglobin A1c (HbA1c) result.

The World Health Organization published revised guidelines on the diagnosis of diabetes, which were accepted for use by Diabetes UK from 1st June 2000.

Algorithm for Diagnosis of Diabetes

1. Classical symptoms (e.g. polyuria, polydipsia, unexplained weight loss) plus one of the following:

random plasma venous glucose concentration ≥11.1 mmol/Lor
fasting plasma venous glucose concentration ≥7.0 mmol/L
plasma venous glucose concentration ≥11.1 mmol/L (2 hour sample in OGTT)

2. No symptoms i.e. incidental finding of glycosuria or hyperglycaemia

Diagnosis should not be based on a single venous plasma glucose measurement
Additional testing on another day with a value in the diabetic range is essential (using either fasting, random or samples taken 2 hours following glucose load)
If fasting or random values are not diagnostic, the 2-hour value should be used

3. If ketonuria is present with:

Severe symptoms i.e. vomiting and dehydration, urgent hospital admission is required.
Milder symptoms and weight loss discuss patient urgently with the diabetes team for consideration of insulin therapy.

For Urgent Hospital Contact Numbers view Nearest Specialist Clinic

Diagnostic Criteria not met?

If fasting glucose is 6.1 – 6.9 mmol/L, consider performing an Oral Glucose Tolerance test (see later)