Glucose Tolerance, Gestational Screen 1 Hour (50g)

Sunquest Code:GLU1  
Epic Code:LAB3503Epic Name:Glucose Tolerance, Gest Screen1 Hour
Synonyms:GTT; Glucose Challenge
Methodology:Bichromatic endpoint, glucose oxidase
St Johns/St Joseph/Woodwinds: Hexokinase
Test Includes:Blood glucose level collected one hour after ingestion of 50 g glucose
Turnaround Time:Performed Mon-Fri, 0700-1700; turnaround time is 2 hours routine, 40 minutes stat.
Special Instructions:This is a screening test usually administered between 24-28 weeks of pregnancy.
Associated Links:

Glucose Tolerance Testing

Collection Instructions

Optimal Volume:2.5 mL
Minimum\Peds Volume:0.6 mL
Container:Green (lithium heparin, gel), St Johns/St Joseph/Woodwinds - Gray Na Fluoride) (Green (lithium heparin, no gel), Red (no gel), Red or gold (gel), St Johns/St Joseph/Woodwinds-Green (lithium heparin, no gel), St Johns/St Joseph/Woodwinds - Red (no gel), St Johns/St Joseph/Woodwinds - Purple (EDTA))
Collection Instructions:Outpatient Laboratory will collect specimens in green top (heparin) or red/black top (gel) tubes to avoid hemolysis. For Women's Health Clinic: 1) WHC will drop off request form to be filed in the future order file. 2) Patient will check into the lab to drink the 50g glucola (no blood is drawn pre-glucola for the 50g screen). 3) OP Lab will set the timer for 1 hour. 4) OP Lab will send a lab staff to WHC to draw the 1 hour post sample and other labs if needed.
Patient Preparation:Patient does not need to be fasting and needs no preparation. The gestational diabetic screen is performed without regard to last meal or time of day.
Contraindications:If patient becomes ill or vomits, test must be discontinued.

Processing and Shipping

Specimen Processing:Centrifuge and aliquot 1.25 mL, 0.2 mL minimum. Store in refrigerator.
Shipping Instructions:Ship at refrigerated temperature.
Stability:Once separated from cells, Room temperature - 8 hours; refrigerated - 72 hours.
Test Performed at or Referral Lab Chemistry  (University of Minnesota Health Maple Grove Clinics, Range, UMMC-East Bank, Oxboro Bloom, Lakes, Ridges, Northland, Southdale, UMMC/UMMCH-West Bank, Clinics, M Health Clinic and Surgery Center, Grand Itasca, St. Joseph's, St. John's, Woodwinds)


Critical Range:
St Johns/St Joseph/Woodwinds <60 mg/dL ≥400 mg/dL
All other sites <40 mg/dL >500 mg/dL
Reference Range:

Reference value at 1 hour less than or equal to 130 mg/dL following 50 g glucose load. This is a screening test for gestational Diabetes Mellitus. If results are abnormal a Standard Gestational Glucose Tolerance test should be ordered.



A fasting glucose greater than 126 mg/dL or a casual plasma glucose greater than 200 mg/dL meets the threshold for the diagnosis of diabetes if confirmed on a subsequent day and precludes the need for a glucose challenge. In the absence of this degree of hyperglycemia, evaluation for GDM in women at average or high risk should follow one of two approaches.


Two-Step Approach:

Perform initial screening with glucose challenge (GCT), a plasma/serum glucose 1 hour after 50 g oral glucose load. Perform a gestational oral glucose tolerance (OGTT) on the subset of women exceeding the glucose threshold value on the GCT. A glucose greater than or equal to 140 mg/dL on the GCT identifies approximately 80% of women with GDM, and the yield is further increased to 90% by using a cutoff of greater than or equal to 130 mg/dL.


One-Step Approach:

Perform gestational oral glucose tolerance test (OGTT) without prior screening.


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