Glucose tolerance test

 

Alternative names, keywords

GTT, OGTT

Samples required

 Fluoride oxalate venous blood (grey cap, 2 mL tube), fasting and 2h post glucose load. Smaller tubes are available for paediatric samples.

For GTT protocol see dynamic function tests.

Test indications

Diagnosis of diabetes mellitus in cases where fasting or random blood glucoses and clinical picture are not diagnostic.

Test information

For RSCH and PRH requests, test can be done by appointment with Phlebotomy - call ext. 64454 at RSCH or 68321 at PRH.

Reference range

Fasting ranges - see glucose (plasma)

2h plasma glucose (non-pregnant)

<7.8 mmol/L

Non-diabetic

7.8 - 11.1 mmol/L

Impaired glucose tolerance

≥ 11.1 mmol/L

Diabetes

Asymptomatic patients require an additional plasma glucose (fasting, random or 2h OGTT) in the diabetic range on a separate day for diagnosis of diabetes.

Source: Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia - WHO 2006
 
 

2h plasma glucose (pregnant)

Gestational diabetes is diagnosed by a 2h plasma glucose 7.8 mmol/L or above.
Source: NICE NG3 February 2015

 

Turnaround time

1 day

Enquiries

Biochemistry (Automation)

 

Details