Department
Chemical Pathology
Delphic Registration Code (Alpha Code)
AAAA
Test Code (Numeric Code)
0000
Laboratory Handling
Phlebotomy
Collect 1 fasting sample and another after 2 hours- 4ml Fluoride Tube (grey top)
Transport
Specimens must be transported immediately to the Laboratory
Sample Stability
TF
Associated Tests
Synonyms
GTT, Oral glucose tolerance test, OGTT, Gestational diabetes screen, GDM
Turnaround Time
2 hours
Specimen Type
- Plasma
Specimen Requirements
Tube/Container Type:
Preferred
- Fluoride (Grey Cap)
Preferred Sample Volume (ml)
4
Paediatric Specimen Requirements
Tube/Container Type:
Preferred
- Fluoride (Grey Cap)
Pre-testing Requirements
Patient preparation:
• Normal, unrestricted carbohydrate diet for at least 3 days
• The test generally should NOT be offered to patients within 2 weeks of a major surgery, trauma, infection, or an acute illness. If the patient is currently unwell e.g. suffering from a cold, advise to rebook for another time after they are feeling better.
• Patients who previously had gastric bypass surgery generally should NOT have this test.
• The requesting doctor should have reviewed the existing medications the patient is on to see if any of them might need to be temporarily withheld in order not to render the test invalid.
• Overnight fast:
- Desirable duration of fasting is 8 – 16 hours (i.e. no food, alcohol, coffee and gum)
- Plain water to quench thirst is allowed from the time of fasting up to 1 hour prior to the test
- If the patient has fasted for more than 16 hours, will need to reschedule.
- The test ideally should commence between 7:00 – 9:00 am. Patients who arrive after 10:30am will need to reschedule.
- Smoking or exercise is NOT allowed within 1 hour prior to the test.
Procedure:
• Fasting blood into first fluoride tube. Timing starts upon the first intake of the glucose drink (dose - see below).
• The patient should stay at the waiting area and continuously abstain from coffee, alcohol, food, gum, smoking or exercise throughout the procedure.
• Collect the second fluoride tube for glucose testing at 120 minutes.
• Both specimens should be transported promptly to the Biochemistry laboratory
A. Adults: consume the entire 75g, 350ml Gluco-TT solution within 5 minutes.
B. Children (age <16 years): 1.75 grams glucose / kg weight, up to maximum of 75 grams (i.e. if the patient weighs ≥43 kgs the top dose should be 75 grams). The solution should be consumed within 5 minutes.
Note: the dose for testing Growth Hormone excess is different: 2.35 grams glucose / kg body weight, up to maximum of 100 grams (i.e. if the patient weighs ≥43 kgs the top dose should be 100 grams). The solution should be consumed within 10 minutes.
Last updated: 13/05/2026