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Laboratory: Clinical Biochemistry  (AUTOMATED)
Test Name:
Test Code: GT50
Clinical Information:
Alternate Name(s): Glucose gestational diabetes screen
Description: Pregnant woman consumes 50 g glucose drink in non-fasting state (any time of the day) and blood collected at 1 hour post-drink for plasma glucose.
Time zero is start of the drink consumption, and 2-hour collection must be ±10 minutes.
Glucose dose: 50 g glucose
50g GCT is the 1st tier screening test for GDM, as defined in Preferred Approach by 2018 Diabetes Canada Guidelines
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.

Patient preparation instructions:  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 

Collection Devices:
Specimen Required:

Plasma: 0.2 mL

Special Processing: Specimen must be centrifuged, and plasma separated from cells within 30 min after collection. Delay (>30 minutes) causes decrease in glucose levels and potentially missed diagnosis of diabetes.
Serum: 1.0 mL
Reference Values:
Plasma glucose, mmol/L Interpretation
<7.8 Normal.
>11.1 Diagnosis of GDM. Confirmation with 75g OGTT is not required.
7.8-11.0 Screen for GDM is positive, follow-up with confirmatory 75g OGTT.

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
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