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GLUCOSE TOLERANCE TEST, PLASMA

Synonym(s):

Lab Section Category

Description

Indications

Specimen Required

​3 mL sodium fluoride/potassium oxalate blood.

Collect 2 timed specimens (fasting and 2-hour post glucose load)

Storage and Transport

Method

​Enzymatic/Oxygen electrode

Test Results

Reference Interval / Value

​Current criteria based on recommendations by WHO and 2006 Miinistry of Health Singapore Clinical guidelines for diagnosis of diabetes mellitus (both for children and adults) involved fasting of 2-hour post glucose venous plasma glucose levels which are summarised as:

Fasting plasma glucose
(mmol/L)
2 hr plasma glucose
(75g oral intake) (mmol/L)
​Diabetes ​≥ 7.0 ​and/or​≥11.1
​Impaired glucose tolerance (IGT) ​< 7.0​and7.8 – 11.0 ​
​Impaired fasting glycaemia (IFG)​ 6.1 – 6.9​and​< 7.8
​Normal ​< 6.1  ​< 7.8

Pregnant women who meet WHO criteria for diabetes mellitus or IGT are classified as having gestational diabetes mellitus. After the pregnancy ends, the women should be reclassified as having either diabetes mellitus, IGT or normal glucose tolerance based on the results of a 75g oral GTT, 6 weeks or more after delivery.

Turnaround Time

​Mean = 4 hrs, Range: 3 – 5 hrs

Day(s) Test Set up

​Daily

Remarks

​The oral GTT should be performed on the morning after at least 3 days of unrestricted diet (greater than 150 g of carbohydrate daily) and usual physical activity.

Fast patient for 8-14 hours overnight. Collect 3 mL fasting blood specimen. Administer 75 g anhydrous glucose in water orally over the course of 5 minutes. Patient should engage in minimal physical activity, no eating and no smoking after glucose is administered. Collect a second blood specimen 2 hrs after the test load.

For children, the oral glucose load should be related to body weight: 1.75 g/kg up to a maximum of 75g. For pregnant women, a standard oral GTT should be performed after overnight fasting by giving 75g anhydrous glucose in 250 - 300mL water.

Change History Notes

Others

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