The pregnant patient consumes a 50 g glucose drink in non-fasting state (any time of the day) and blood is collected at 1 hour post-drink for plasma glucose. The entire drink must be consumed within 5 minutes for the test results to be valid.

Time zero = once entire drink has been consumed

1-hour collection must be ±10 minutes from expected collection time

Test Indications: All pregnant patients 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.

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:  

·        The patient should not be dehydrated prior to testing.

·        The patient does not need to be fasting

·        The patient should be prepared to sit/rest for the entire duration of the test. No walking or exercise, as this may lead to falsely lower glucose results.

·        The 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 

 

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