Please note : Patient must phone collection centre in advance as an appointment is essential for this test.      

For paedatric GTT refer to collection information below.

Paediatric GTT

GLUCOSE TOLERANCE TEST  

Please note : Patient must phone collection centre in advance as an appointment is essential for

Patient Collection Instructions - English

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Patient Collection Instructions -Simple Chinese

Patient Collection Instructions - Trad. Chinese

Patient Collection Instructions - Dinka

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Patients are tested for their ability to handle an oral glucose load taken in fasting state by measuring their plasma glucose 2-hours after ingestion.

Patient should be on their normal diet until the day of the test

 The test is done at a time when the patient is free of acute illness

 The test is performed between 0800 and 1000 after a 12-hour overnight fast. Water is permitted during the fasting period but eating, physical activity and smoking must be avoided

 If fasting sample is less than 8mmol/L - proceed with the test

 A 75g glucose load in the form of a single 285 mL bottle of chilled Dextrasol. The time and date of ingestion is noted.

 Ingestion should be completed within 5 minutes.

 Two more venous blood samples are taken at 1-hour intervals, starting exactly 1 hour after completion of ingestion.

Please contact laboratory on 9895 3471 for queries relating to GCT and GTT testing.

GROWTH HORMONE SUPRESSION TEST (OGTT with Growth Hormone/ IGF-1)

Take baseline samples of blood for IGF-1, glucose and GH.

Give bottle of 75 g glucose (or appropriate amount if paediatric patient) which should be drunk within 5 minutes.

Samples are collected at 30, 60, 90 and 120 minutes for glucose and Growth Hormone. 

The vast majority of Oral Glucose Tolerance Tests (OGTTs) requested are for the diagnosis of glucose intolerance and should be performed and interpreted according to Australian guidelines with fasting, 1hr and 2hr glucose measurements following a 75g glucose load. A small number of requests require variations in this standard protocol and staff must carefully check the request slip to ensure that the correct protocol is followed and the appropriate specimens collected.

Where the doctor has requested  ?OGTT ? fasting and 2hour only? then it is o.k. to omit the 1 hour bloods.

?OGTT with insulin? is used to investigate insulin resistance. This requires glucose and insulin levels at each time point (i.e. 0, 1 and 2 hours).

?OGTT with Growth Hormone/ IGF-1? is used to diagnose and monitor Acromegaly. This requires glucose and Growth Hormone levels at 30, 60, 90 and 120 minutes.

Diagnostic Criteria for Diabetes Mellitus

(World Health Organisation 1999)

Gestational diabetes mellitus (GDM):a diagnosis of GDM is made if one or more of the following glucose levels elevated.

Fasting: >=5.1   1 hour: >=10.0  2 hour: >=8.5-11.00

Reference

MJA 1991; 155:112 Med J Aust 15-Apr-1999; 170:375-8