Changes to Terminology and Diagnostic Criteria
Diagnostic Criteria
Notes Concerning Testing
Screening For Type 2 Diabetes
References

Changes to Terminology and Diagnostic Criteria                 (top of page)

The criteria for the diagnosis of Diabetes Mellitus have recently been updated (1). The changes include adjustments to definitions and classification as well as diagnosis (2). These changes are incorporated into a screening plan supported by Diabetes Australia and the Commonwealth Government (3). A brief summary of the changes and new recommendations follows:

Terminology

Type 1 and 2 diabetes replace the terms IDDM and NIDDM respectively. Type 1 indicates beta cell destruction, usually leading to absolute insulin deficiency, and type 2 covers a range from predominantly insulin resistance with relative insulin deficiency to a predominantly secretory defect with or without insulin resistance. The category Gestational Diabetes Mellitus is retained as a separate category. Other specific causes of diabetes, eg genetic defects, drug-induced, pancreatic injury, endocrinopathies are listed separately (2).

New Category

A new category called "Impaired Fasting Glucose" has been introduced. This category is analogous to "Impaired Glucose Tolerance" in indicating a metabolic stage between normal glucose homeostasis and diabetes. These states are risk factors for the development of diabetes and cardiovascular disease. Impaired Fasting Glucose is defined by a fasting glucose concentration between 6.1 and 6.9 mmol/L (inclusive).

Change to the diagnostic criteria

The concentration of glucose in a fasting plasma sample required for diagnosis of diabetes has been lowered from 7.8 to 7.0 mmol/L.

Diabetes Mellitus is diagnosed if any of the following criteria are satisfied:

1. Symptoms of diabetes (polyuria, polydipsia, unexplained weight loss) and random plasma glucose >/= 11.1 mmol/L.

2. Fasting plasma glucose >/= 7.0 mmol/L

3. Oral Glucose Tolerance test: 75 g glucose, 2 hour plasma glucose result >/= 11.1 mmol/L.

In the absence of unequivocal symptoms, or if the glucose level is borderline, diagnosis by criteria 1 or 2 should be confirmed by repeat testing on a separate day.

Impaired Glucose Tolerance is diagnosed if a plasma glucose result 2 hours after a 75g glucose load is between 7.8 and 11.0 mmol/L (inclusive).

Impaired Fasting Glucose is diagnosed if a fasting plasma glucose result is between 6.1 and 6.9 mmol/L (inclusive).

1. Patients must be fasting for at least 8 hours to apply the fasting criteria.

2. The criteria apply to persons who are otherwise well at the time of diagnosis. Physiological stress from infection, trauma or other illness, or the effect of some drugs may cause false positive results. In general the criteria should be applied to ambulant outpatients only.

3. Samples for plasma glucose should be separated from red cells as soon as possible after collection. When there may be a delay greater than one hour prior to centrifugation, samples must be collected into fluoride-oxalate tubes (grey-top). Even with these tubes a fall in plasma glucose of 0.1-0.2 mmol/L may occur.

4. The criteria apply to venous plasma samples. Capillary or whole blood samples may require alternate decision points depending on the analysis method used.

5. Haemoglobin A1c and home blood glucose meters are not appropriate methods for the diagnosis of diabetes.

6. A fasting plasma glucose less than 5.5 mmol/L indicates a low probability of diabetes.

• <5.5 mmol/L - diabetes is unlikely - offer lifestyle advice and re-test in 5 years.

• 5.5 - 6.9 mmol/L - diabetes is uncertain Glucose tolerance testing or more frequent fasting glucose indicated.

• >/= 7.0 mmol/L - diabetes likely - confirm with repeat fasting glucose unless clinically unequivocal.

1. Medical Journal of Australia, 1999; 170: 375-8. New Classification and Criteria for diagnosis of Diabetes Mellitus. Position statement from the Australian Diabetes Society, the New Zealand Society for the Study of Diabetes, the Royal College of Pathologists of Australasia and the Australasian Association of Clinical Biochemists.

2. Diabetes Care, 1997;20:1183-97. Report on the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus.

3. www.difusediabetes.info.au