ORAL GLUCOSE TOLERANCE TEST (OGTT), 75 g – GESTATIONAL DIABETES (GDM) - (P)

Test Code: GTTP

Alternate Name(s): Glucose tolerance test (gestational)

Description: This test is performed as a follow-up test for positive 50 g Glucose Challenge Test (GCT).
75g OGTT is the 2nd tier test for GDM, as defined in Preferred Approach by 2018 Diabetes Canada Guidelines
 
75 g OGTT includes collection of fasting plasma glucose after an 8-hour fast, followed by consumption of glucose drink, and blood collected at 1 hour and 2 hours post-drink for plasma glucose.
 
Time zero is start of the drink consumption, and timed collection must be ±10 minutes.

Test Indications: All pregnant women without known pre-existing diabetes should be screened for gestational diabetes mellitus (GDM) at 24 – 28 weeks of gestation. GDM is defined as hyperglycemia with onset or first recognition during pregnancy. The global prevalence of hyperglycemia during pregnancy has been estimated at 16.9% using WHO criteria.  Between 3% to 20% of pregnant women develop gestational diabetes.
 
Untreated GDM carries short-term (preeclampsia, preterm delivery) and long-term (obesity, diabetes, cardiovascular disease) health risks for both mother and baby, while treatment reduces these adverse outcomes.

Recommendations: Diabetes Canada Clinical Practice Guidelines Expert Committee. Diabetes Canada 2018 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada. Can J Diabetes. 2018;42(Suppl 1):S1-S325.
https://guidelines.diabetes.ca/cpg

Patient preparation instructions:
Minimum 8h fasting (only water permitted)
Patient should not be dehydrated prior to testing
Patient should be prepared to sit/rest for the duration of the test. No walking or exercise.
Patient should bring a snack to have after test completion.
Some labs perform this test by appointments only. Call in advance to inquire.
Consult your physician if any of the medication should be discontinued prior to testing.

PB110-10-17 Patient Brochure Fasting GTT 

_SH Biochemistry Hematology Requisition (R250-10-92)

_SH Hospital Biochemistry Hematology Non Winnipeg Brandon (R250-10-91)

_SH Winnipeg Brandon Biochemistry Hematology Requisition (R250-10-94)

_SH Winnipeg Brandon Hospital Biochemistry Hematology Requisition (R250-10-93)

GDM is diagnosed using one or more of the following criteria:
 

Sample	Criteria
Fasting PG	≥5.3 mmol/L
1 h PG	≥10.6 mmol/L
2 h PG	≥9.0 mmol/L

PG, plasma glucose

Critical Value: Glucose:
<2.5 mmol/L or >25 mmol/L

Method of Analysis: Glucose:
Roche Cobas - Photometric/Hexokinase + G6PDH
Ortho Vitros - Photometric/Glucose Oxidase + peroxidase

Weekdays, by Prior Arrangement Only

GLUCOSE - (P)

ORAL GLUCOSE TOLERANCE TEST (OGTT), 75 g – GESTATIONAL DIABETES (GDM) - (P)

GLUCOSE CHALLENGE TEST (GCT), 50 g – GESTATIONAL DIABETES(GDM) - (P)