Laboratory Test Information Guide

Details for Glucose Tolerance Test

Test Name: Glucose Tolerance Test
Alternate Name(s): GTT
Gestational Glucose Tolerance Test
Laboratory: Core
Specimen Type: 4.5 mL Green top Vacutainer tube
4.5 mL grey top tube
Pediatric:
0-2 years: 0.6 mL Green pk.
2-10 years: 3 mL Green top
Collection Information: 
Paediatric:
Prebook with Paediatric Medical Day Unit,VH, Ext. 58434.

Instructions for 1 hour 50g Glucose Tolerance Test:
Patient must drink entire contents at once. Nothing to eat or drink from the time of the drink until the time the post consumption (PC) blood is drawn. PC glucose level must be drawn EXACTLY 1 HOUR AFTER FINISHING THE DRINK

No urine samples are required.

Notes: No urine samples are required.
Fasting not necessary for the 50g Glucose Tolerance Test
Fasting required for the 75g Glucose Tolerance Test - No caloric intake for at least 8h before the test.
Requisition: GENERAL LABORATORY REQUISITION
Test Schedule: Monday - Friday
0800 - 1600 h
Turnaround time from when specimen
is received in testing laboratory:
 
Routine
4 hours
Stat
 
 
Reference Range: * See Interpretive Comments for the diagnosis of Diabetes Mellitus
Effective Date: 2007-01-11
Revised Date: 2019-04-01
Critical Value:  
Interpretive Comments: *Diagnosis of Diabetes (Non-pregnant Adults)
Fasting Glucose: ≥ 7.0 mmol/L or
2 h Glucose after 75 g load: ≥ 11.1 mmol/L or
Random PG ≥11.1 mmol/L
(Random = any time of the day, without regard to the interval since the last meal)

Impaired fasting glucose:
Fasting glucose:
6.1-6.9 mmoL/L

Impaired glucose tolerance:
2 h Glucose after 75 g load:
7.8-11.0 mmol/L

Gestational Diabetes Screening:
50 g Glucose Tolerance Test:
1hr Glucose after 50g load: <7.8 mmol/L - Normal
1hr Glucose after 50g load: 7.8 - 11.0 mmol/L then proceed to 75g glucose tolerance test
1hr Glucose after 50g load: ≥ 11.1 mmol/L is diagnostic of GDM

75g Glucose Tolerance Test: (Two step approach)
Fasting Glucose ≥ 5.3 mmol/L
1hr Glucose after 75g load: ≥ 10.6 mmol/L
2hr Glucose after 75g load: ≥ 9.0 mmol/L
GDM is diagnosed if one value of the three above is met or exceeded.

75g Glucose Tolerance Test: (One step approach)
Fasting Glucose ≥ 5.1 mmol/L
1hr Glucose after 75g load: ≥ 10.0 mmol/L
2hr Glucose after 75g load: ≥ 8.5 mmol/L
GDM is diagnosed if one value of the three above is met or exceeded.

Please see 2018 CDA guidelines at
http://guidelines.diabetes.ca/cpg

Special Processing: Cerner Codes

Glucose Tolerance - GTT2
Gestational Glucose Tolerance - GTTG1/GTTG2
Comments:  
Method of Analysis: Oxygen rate method
Critical Information Required:  
Storage & Shipment:  
System Codes: 
Cerner
See Special Processing
 
Referred To:  

Questions? Comments? Contact Laura Gopaul