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Diabetes is diagnosed either by measurement of HbA1c or glucose in blood (or more correctly in plasma which is the fluid left behind when cells have been removed from blood) in accordance with the criteria of the Australian Diabetes Association and the World Health Organisation.
Diagnostic criteria; A diagnosis of diabetes is made if one or more of following values are elevated.
- A random venous plasma glucose concentration ≥ 11.1 mmol/l or
- A fasting plasma glucose concentration ≥ 7.0 mmol/l or
- Two hour plasma glucose concentration ≥ 11.1 mmol/l in an oral glucose tolerance test (OGTT) or
- An HbA1c of ≥ 48mmol/mol (6.5%)
A single elevated test result is adequate for diabetes diagnosis if the patient is symptomatic. However, in the absence of typical symptoms repeat testing on another day is required for confirmation. If the fasting or random glucose concentrations do not fall into the criteria given above then an OGTT should be performed. The OGTT involves a fasting glucose, followed by the patient drinking a standard amount of a glucose solution to ‘challenge’ their system, followed by another glucose test two hours later.
|Table of reference intervals for OGTT
||2 hour glucose
|Impaired glucose tolerance
||7.8 - 11.0 mmol/L
|Impaired fasting glycaemia
||6.1 - 6.9 mmol/L
|Diabetes mellitus in the prescence
of symptoms or repeated
diabetic glucose level
The HbA1c test does not require any patient preparation and can be performed at any time of day.
All women not known to have DM or GDM should have a standard 75 g OGTT at 24–28 weeks gestation.
In pregnancy OGTT apart from fasting and 2 hour plasma glucose, an extra plasma glucose at one hour is performed. The diagnostic glucose levels are lower in pregnant women.
The ADIPS 2014 and IADPSG criteria for the diagnosis of GDM; A diagnosis of GDM could be made on one or more of these values:
Fasting >5.1 mmol/L
1 hour > 10.0 mmol/L
2 hour ≥ 8.5 mmol/L
Previous ADIPS Guidelines (Hoffman 1998, ADIPS 1998) for the Testing and Diagnosis of Gestational Diabetes Mellitus in Australia are still in use among some clinicians:
Fasting ≥ 5.5 mmol/L
2 h glucose ≥ 8.0 mmol/L
Sometimes random urines are tested for glucose, protein and ketones during a routine clinical examination using a 'dipstick test'. If glucose and/or protein or ketones is present on the dipped indicator strip then further investigations are necessary. This screening tool is not sensitive enough for monitoring patients who have been diagnosed as diabetic.
Tests for diabetes monitoring
Several laboratory tests may be used to monitor diabetes on a regular basis.
Glucose: Diabetic patients can monitor their condition by measuring their own blood glucose (capillary) levels. Self-monitoring of blood glucose (targets 6–8 mmol/L for fasting and 6–10 mmol/L for two hour postprandial) Capillary blood glucose results are lower compared with venous plasma glucose results.
Measurement of capillary blood glucose is recommended only for type 1 diabetes or people with type 2 diabetes who are on insulin injections or pregnancy complicated by pre-existing diabetes or gestational diabetes mellitus (GDM).
Home blood measurements are done by placing a drop of blood (obtained by pricking the finger with a small lancet device), onto a plastic glucose test strip and then inserting the strip into a small test meter, which provides a digital readout of the blood glucose. Glucose measurements can be taken several times a day at a frequency which depends on how well their blood glucose concentration is controlled.
Haemoglobin A1c (HbA1c) - (Target ≤7% (≤53 mmol/mol)
Fructosamine- evaluates average glucose levels over the past 2 to 3 weeks
1,5-anhydroglucitol, 1,5-AG (or GlycoMark test) - is a new test that detects high glucose levels in the past 1 to 2 weeks. 1,5-Anhydroglucitol (1,5-AG) is predominantly of dietary origin. After its absorption, it is excreted by the kidney. When the blood sugar is high, urinary reabsorption of 1,5-AG is impaired, urinary excretion increases, and blood concentrations decline; therefore, 1,5-AG is a short-term marker of hyperglycaemia after meals that are not shown by HbA1c and fructosamine tests. The only other way to get this information is by frequent fingerprick blood glucose testing. Decreased 1,5-AG may particularly reflect postprandial hyperglycaemia (high blood sugar after eating). 1,5-AG may be useful to assess glycaemic control in patients haemoglobinopathies.
To monitor kidney function: Creatinine, eGFR, creatinine clearance, UACR (urine albumin creatinine ratio), Cystatin C, BUN, CMP
To monitor lipids: Triglycerides, cholesterol, HDL cholesterol, LDL cholesterol, Lipd profile
Last Review Date: August 1, 2018