Glucose Tolerance Test, 75 g

Alternative Names/Synonyms	2-hour OGTT, OGTT, Oral Glucose Tolerance Test
Laboratory	Core Laboratory & Transfusion Medicine
Sub-section	Biochemistry
Specimen Type	Blood
Test Code	GTTP2

Ordering Instructions, Requisition

This test is by appointment only.

Clinical Significance

Screening and diagnosing gestational diabetes mellitus (GDM).

Specimen Requirements (Sample Type)

Plasma

Specimen Requirements (Volume (mL))

0.5 mL

Specimen Requirements (Tube Type)

Plasma (Grey Tube)
Collection Containers – Tube Types

Collection Requirements

Blood Collection Instructions

Sample Stability

Room Temperature: 3 days

Cause for Rejection

Specimen Acceptability and Transport Guidance

Instrument, Methodology

Roche cobas c 702, enzymatic

Test Availability

Weekdays

Routine Turnaround Time

3 hours

Reference Ranges

A diagnosis of GDM is confirmed with one or more of the following glucose results:

Fasting > 5.3 mmol/L
1 hour > 10.6 mmol/L
2 hour > 9.0 mmol/L

In case of discrepancies, always interpret results using reference ranges as stated on laboratory reports and/or electronic patient chart.

Laboratory Contact Information

416-586-4800 extension 8070

Patient Preparation

Patient must be fasting for at least 8 hours prior to testing.

Ordering Practices

This should only be performed subsequent to a Glucose Challenge Test, 50 g between 7.8 - 11.0 mmol/L.

References

1. https://guidelines.diabetes.ca/cpg/chapter36