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Glucose Tolerance, 2-Hour, (75 g Gestational)

Pregnancy GTT 2-hour 75 g, 2-hour Pregnancy Glucose Tolerance Test 75 g, Pregnancy Glucose Tolerance Test, 2-Hour 75 g

Test Codes

EPIC: LAB1230278, Beaker: GLTP2, Antrim: 13285

Department

Chemistry

Instructions

• This test must be scheduled through the Beaumont Appointment Center at 800-328-8542.
• Be sure the requisition indicates "Pregnancy 2-Hour Glucose Tolerance Test (75 g)."

Patient Preparation

• The patient should be on a full, well-balanced diet (80 g protein and at least 150 g carbohydrates) for 3 days prior to the test.
• The patient should fast after the evening meal the night before the test. (Fasting for at least 8 hours.)
• The test should be done in the morning before the patient has exercised.
• The patient should not exercise or smoke during the test.
• A few small sips of water are acceptable.

Specimen Collection Criteria

Collect: One Gray-top Potassium Oxalate / Sodium Fluoride tube prior to administration of the oral glucose load, and at each hour interval, as outlined below.

Also acceptable: One Gold-top SST tube or Microtainer^® drawn under the same guidelines as listed above and below. SST tubes and Microtainers^® must be centrifuged within 1 hour of collection. Contact the Laboratory for acceptability of other tube types. 

• After the fasting glucose is drawn, the specimen is assayed. If the value of the fasting glucose for a pregnant patient is 140 mg/dL or greater, the glucose tolerance test will be canceled and only the fasting glucose value will be reported. This policy will prevent the unnecessary administration of an oral glucose load to a non-fasting or overtly diabetic patient. If the value is less than the above cutoff value, the appropriate dose of glucose will be given.
• Administer Dose: The proper oral glucose does is 75 grams.
• In addition to the fasting specimen, blood should be collected at 1 and 2 hours after glucose load. Record the exact time of collection on the tube. Specify if the specimen is fasting, 1 hour or 2 hours.

Physician Office/Draw Specimen Preparation

Maintain Gray-top tubes refrigerated (2-8°C or 36-46°F) prior to courier transport. (Minimum: 0.5 mL)

Let SST specimens clot 30-60 minutes then immediately centrifuge to separate serum from cells. Refrigerate (2-8°C or 36-46°F) the centrifuged SST tube within two hours of collection. (Minimum: 0.5 mL)

Preparation for Courier Transport

Transport: Centrifuged SST tubes or Gray-top tubes refrigerated (2-8°C or 36-46°F). (Minimum: 0.5 mL each tube)

Rejection Criteria

• Grossly hemolyzed specimens.
• Inadequately centrifuged Microtainers^® or Gold-top tubes.
• Specimens collected in any tube other than an SST or Gray-top tube.
• SST samples in which serum has not been separated from cells within 1 hour of collection.
• Gray-top tubes that are not received within 24 hours of the time of collection.
• Specimens not collected and processed as indicated. 

In-Lab Processing

Let SST specimens clot 30-60 minutes. Centrifuge SST, Gray-top tubes, or Microtainers^® to separate serum or plasma from cells. Deliver immediately to the appropriate testing station.

Storage

Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers^® with Separator Gel
Room Temperature (20-26°C or 68–78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Gray-top Tubes
Room Temperature (20-26°C or 68-78.8°F): 24 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68–78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 7 days

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Dearborn Chemistry Laboratory
Farmington Hills Chemistry Laboratory 
Grosse Pointe Chemistry Laboratory 
Royal Oak Automated Chemistry Laboratory 
Troy Chemistry Laboratory
Taylor Chemistry Laboratory
Trenton Chemistry Laboratory
Wayne Chemistry Laboratory 

Performed

Monday – Saturday.
Results available within 24 hours of receipt in the Laboratory.

Reference Range

Guidelines for Interpretation:

Normal cut-offs for a 2-Hour Pregnancy Glucose Tolerance Test are listed below. Results are considered indicative of gestational diabetes if any one of these is exceeded.

Fasting: 60-91 mg/dL.
1 Hour: 60-179 mg/dL.
2 Hour: 60-152 mg/dL.

Test Methodology

Enzymatic.

Clinical Utility

The American Diabetes Association (ADA) recently recommended that screening for gestational diabetes should be performed at 24-28 weeks gestational age using a 2-Hour Glucose Tolerance Test (GTT) with 75g Glucola. However, this approach is not currently recommended by ACOG. The pregnancy glucose tolerance test is used to predict perinatal morbidity in pregnancy. This assay aids in the diagnosis of gestational diabetes. Risks of fetal abnormality and perinatal mortality are increased with abnormal carbohydrate metabolism in pregnancy.

CPT Codes

82947, 82950.

Contacts

Last Updated

10/28/2024