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The WHO Definition, Diagnosis
& Classification of Diabetes Mellitus and its Complications
Summary of Changes
The main changes of the new
recommendations are set out below. They include the recommendation that the cut off point
for diagnosing diabetes using a fasting plasma glucose should be lowered from 7.8 mmol/l
to 7.0 mmol/l. This change reflects research evidence regarding the development of the
complications of diabetes.
Criteria for diagnosing diabetes mellitus:
Diabetes symptoms (i.e. polyuria, polydipsia and unexplained weight
loss) plus
- a random venous plasma glucose concentration >=11.1 mmol/l
or
- a fasting plasma glucose concentration >=7.0
mmol/l. (Whole blood
>=6.1mmol/l) or
- 2 hour plasma glucose concentration >=11.1
mmol/l 2 hours after 75g
anhydrous glucose in an oral glucose tolerance test (OGTT)
- With no symptoms, the diagnosis should not be based on a single
glucose determination but requires confirmatory plasma venous determination.
At least one additional glucose test result on another day with a value in the diabetic
range is essential, either fasting, from a random sample or from the two hour post glucose
load. If the fasting or random values are not diagnostic an OGTT should be undertaken and
the 2-hour value used.
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Classification and terminology:
Insulin-dependent and non-insulin dependent diabetes will be renamed
Type 1 and Type 2 diabetes.
The terms Type 1 and Type 2 process will be introduced to describe
the cause of insulin-dependent and non-insulin dependent diabetes respectively. Both of
these pathological processes will be clinically staged by the treatment that they need -
from diet to insulin
Impaired Glucose Tolerance (IGT) is a stage of impaired glucose
regulation (Fasting plasma glucose <7.0 mmol/ and OGTT 2-hour value >=7.8 mmol/l but
<11.1 mmol/l).
Impaired Fasting Glycaemia (IFG) has been introduced to classify
individuals who have fasting glucose values above the normal range but below those
diagnostic of diabetes. (Fasting plasma glucose >=6.1 mmol/l but <7.0 mmol/l). A OGTT
may be considered to exclude the diagnosis of diabetes.
Gestational Diabetes is retained but now encompasses the groups
formerly classified as Gestational Impaired Glucose Tolerance (GIGT) and Gestational
Diabetes Mellitus (GDM). The BDA endorses the use of the WHO definition to allow for
comparative studies. However, since glucose tolerance changes with the duration of
pregnancy, the gestation at which the diagnosis was made should be recorded and, if made
in the third trimester, the clinician should be cautious about the clinical implication of
impaired glucose tolerance
It should be noted that children usually present with severe symptoms
and diagnosis should then be based on a single raised blood glucose result, as above.
Immediate referral to a Paediatric Diabetes Team should not be delayed.
A diagnosis of diabetes has important legal and
medical implications for the patient and it is therefore essential to be secure in the
diagnosis. A diagnosis should never be made on the basis of glycosuria or a stick reading
of a finger prick blood glucose alone, although such tests may be useful for screening
purposes. HbA1c measurement is also not currently recommended for the diagnosis of
diabetes. Diagnosis should always be confirmed by a glucose measurement performed at the
laboratory on a venous plasma sample.
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Oral Glucose Tolerance Test:
If an oral glucose tolerance test (OGTT) is
required, this can be undertaken at either Basildon or Orsett, without prior appointment,
Tuesday to Friday only. The patient should attend in the morning, after at least 3 days of
unrestricted diet (greater than 150 g of carbohydrate daily) and usual physical activity.
Recent evidence suggests that a reasonable (30-50g) carbohydrate meal should be eaten on
the evening before the test and the patient should fast for at least 10 hours
before the test.
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