Test Entry - Detail

Prolonged Glucose Tolerance Test

General
  Clinical Use: A longer GTT that measures glucose at baseline, 1 hour, 2 hours and 3 hours post glucose load. It is used to screen patients for post prandial hypoglycaemia however a mixed meal test is preferable.
It should not be done in patients who are acutely unwell and interpretation may be affected by low carb diets, bariatric surgery and steroid treatments.
  Availability: Samples are tested routinely during the testing laboratory's hours of operation.
  Aliases/Synonyms: Extended GTT,   Extended OGTT,   GTT - Prolonged,   OGTT - Prolonged,   Prolonged Oral Glucose Tolerance Test,  
  Code: GTTP
  Handling Instructions (to laboratory): Send sample chilled.
  Hyperlink:
  Reference Interval: 









Diagnostic Criteria 75g GTT (mmol/L)






Fasting
2 hour




Normal
<=6.0 and
<7.8




Impaired
6.1-6.9 and/or
7.8-11.0




DM
>=7.0 and/or
>=11.1





Diagnostic Criteria 75g GTT in Pregnancy ADIPS 2025 (mmol/L)






Fasting
1 hour
2 hour




Normal
<5.3 and
<10.6 and
<9.0




Gestational DM
5.3-6.9 or
>=10.6 or
9.0-11.0




Overt DIP
>=7.0 or

>=11.1

Collection Requirements
  Container: Fluoride Oxalate (GREY) x 4,  
  Sample Type: See container
  Minimum Collection Volume:
  Collection Instructions: Patient must be fasting.
Adults and children >=43kg are given a 75g glucose load.
For children <43kg, the glucose load should be calculated as 1.75g/kg.
Samples for glucose should be collected at baseline, 1 hour, 2 hours and 3 hours after glucose load.
Occasionally, other protocols may be requested - please contact duty biochemist to confirm before proceeding.
Prolonged OGTT with ½ hourly samples - glucose collected at baseline, 30 m, 60 m, 90 m, 120 m, 150 m and 180 mins post glucose load (code GTTP3)
Prolonged OGTT with insulins - glucose and insulin collected at baseline, 1h, 2h and 3h after glucose load (code GTTIN)
GTT Procedure Slip

Processing Requirements
  Alternate Containers:
  Processing Instructions:
  Minimum Assay Volume: 100uL
  Stability: 7 days chilled
  Transport Instructions (to testing laboratory): Send sample chilled.

Testing Locations
  Performed at:
Section Department Site Contact Phone
- Laboratory Albany Health Campus 9892 2240
- Laboratory Armadale Health Service 9391 2030
- Laboratory Bentley Health Service 9416 3720
- Laboratory Broome Health Campus 9194 2286
- Laboratory Bunbury Hospital 9722 1280
- Laboratory Busselton Hospital 9753 6260
- Laboratory Carnarvon Hospital 9941 0431
- Laboratory Collie Hospital 9734 1132
- Laboratory Derby Hospital 9193 3371
- Laboratory Esperance Health Campus 9079 8139
- Laboratory Geraldton Regional Hospital 9956 2254
- Laboratory Hedland Health Campus 9174 1504
- Laboratory Kalgoorlie Health Campus 9080 5825
- Laboratory Karratha Health Campus 9144 7674
- Laboratory Katanning Health Service 9821 6334
- Laboratory Kununurra Hospital 9166 4245
- Laboratory Manjimup Hospital 9772 5137
- Laboratory Merredin Health Service 9041 1532
- Laboratory Narrogin Hospital 9881 0481
- Laboratory Northam Health Service 9690 1657
- Laboratory Osborne Park Hospital 9244 2326
- Laboratory Rockingham General Hospital 9599 4239
Core Biochemistry Fiona Stanley Hospital 6152 8140
Core Biochemistry Fremantle Hospital 9431 2382
Core Biochemistry King Edward Memorial Hospital 6458 2753
Core Biochemistry QEII Medical Centre 6383 4093
Core Biochemistry Royal Perth Hospital 9224 1176


Last Updated : 29-08-2025 14:02