Info

Source: Adapted from (WHO 1995, 2000, 2004).

Figure 1.2 'Apple'-shaped fat distribution (central obesity with intra-abdominal adiposity) carries a higher cardiovascular and diabetes risk than 'pear'-shaped fat distribution.

Source: Adapted from (WHO 1995, 2000, 2004).

Figure 1.2 'Apple'-shaped fat distribution (central obesity with intra-abdominal adiposity) carries a higher cardiovascular and diabetes risk than 'pear'-shaped fat distribution.

Diagnosing Diabetes 3

diagnosis to be missed for years, and a significant proportion of those with type 2 diabetes remain undiagnosed. Insidious symptoms mean that the patients generally tend to ignore them. This is one reason why complications are often seen at diagnosis in patients with type 2 diabetes. A number of cases with type 2 diabetes are now diagnosed at insurance examinations or through opportunistic testing when the patient has presented for some other problem to the general practice or hospital.

The diagnosis of diabetes must not be taken lightly by a clinician as the consequences for the individual are significant and life-long. For those presenting with severe symptoms, evidence of long-term complications or severe hyperglycaemia at presentation, the diagnosis is quite straightforward and can be made using only one diagnostic blood glucose measurement. In asymptomatic individuals presenting with mild hyperglycaemia, the diagnosis should only be established on the basis of at least two abnormal test results. In future, the recently published recommendation is that HbA1c values will be used rather than plasma glucose as it has been in the past (Box 1.1).

Glucose tolerance test

A glucose tolerance test should be performed in the morning after an overnight fast. It is important that the patient should have had a normal diet for the preceding 3 days and should not restrict carbohydrate intake drastically. The test should also not be performed during an acute illness or following prolonged bedrest. Plasma glucose concentrations are measured fasting and then 2 hours after a drink of 75 g of glucose in 250-350 ml of water (in children: 1.75 g/kg up to maximum of 75 g). Several proprietary preparations are available and these are often flavoured to make items palatable. Table 1.2 shows normal values and interpretation of abnormal values during an oral glucose tolerance test (OGTT). The role of oral glucose tolerance tests is set to change given the recent recommendations over the use of HbA1c as a preferred means of diagnosing diabetes (Box 1.1).

Interpretation of the oral glucose tolerance test results

Impaired fasting glycaemia (IGF)

Fasting glucose between 6.1 and 6.9mmol/l in the absence of abnormal values after the glucose load is defined as impaired fasting glycaemia. Conversion to diabetes is not invariable but it is important to reassess once a year, and in future this is likely to be through HbA1c measurement (see Box 1.1). Individuals with IFG should be advised about a healthy life-style and to avoid obesity.

Impaired glucose tolerance (IGT)

Once again conversion to diabetes is not invariable and patients may either persist with impaired glucose tolerance, revert to normal glucose tolerance or progress to type 2 diabetes. Obese individuals should be advised to try and lose weight through diet and exercise. The implications of this diagnosis for pregnancy are different and this is considered further in Chapter 17.

IGF and IGT are collectively known as impaired glucose regulation but these terms may become outdated as HbA1c becomes the recommended means of diagnosing diabetes and identifying those at risk (see Box 1.1).

Diabetes mellitus

A fasting glucose of greater than or equal to 7.0 mmol/l or a 2-hour glucose value of greater than or equal to 11.1 mmol/l suggests

Table 1.2 WHO criteria for the diagnosis of diabetes mellitus based on venous plasma samples.

Fasting (mmol/l) 2-hour sample following oral glucose challenge (mmol/l) in OGTT

Box 1.1 Recommendation of the International Expert

Committee

For the diagnosis of diabetes:

• The HbAlc assay is an accurate, precise measure of chronic glycaemic levels and correlates well with the risk of diabetes complications.

• The HbAlc assay has several advantages over laboratory measures of glucose.

• Diabetes should be diagnosed when HbAlc is >6.5%. Diagnosis should be confirmed with a repeat HbAlc test. Confirmation is not required in symptomatic subjects with plasma glucose levels >11.1 mmol/l.

• If HbA1c testing is not possible, previously recommended diagnostic methods (e.g. FPG or 2 hour OGTT, with confirmation) are acceptable.

• HbA1c testing is indicated in children in whom diabetes is suspected but the classic symptoms and a casual plasma glucose >11.1 mmol/l are not found.

For the identification of those at high risk for diabetes:

• The risk for diabetes based on levels of glycemia is a continuum; therefore, there is no lower glycemic threshold at which risk clearly begins.

• The categorical clinical states pre-diabetes, IFG, and IGT fail to capture the continuum of risk and will be phased out of use as HbA1c measurements replace glucose measurements.

• Those with HbA1c levels below the threshold for diabetes but >6.0% should receive demonstrably effective preventive interventions. Those with HbA1c below this range may still be at risk and, depending on the presence of other diabetes risk factors, may also benefit from prevention efforts.

(Adapted from: The International Expert Committee. International

Expert Committee Report on the role of the HbA1c assay in the diagnosis of diabetes. Diabetes Care 2009;32:1327-34; 2009)

Impaired fasting glycaemia (IFG) 6.1-6.9 <7.8

Impaired glucose tolerance (IGT) <7.0 7.8-11.0

Diabetes mellitus >7.0 >11.1

Table 1.3 Conversion of DCCT aligned HbA1c measurements to the new IFCC standard.

HbAlc

Table 1.3 Conversion of DCCT aligned HbA1c measurements to the new IFCC standard.

HbAlc

DCCT aligned (%)

IFCC (mmol/mol)

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