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Test Code GTGO or LAB2621 Glucose Tolerance, 2-Hour Gestational Diagnosis - ADA (2 Hr 75 Gm), Serum or Plasma

Important Note

This test is one of two defined by medical professional organizations for diagnosing gestational diabetes. Nonetheless, if a physician orders a glucose tolerance with these same parameters (75 gram, Fasting, 1hr, 2 hr), the test may be ordered on a non-pregnant patient. 

By appointment only. Please call Bronson Central Scheduling at 269-341-8700 to schedule this test.

Patients are permitted to bring in their own glucose powder if the product is Fresh Test 75-gram powder.

Profile Information

Test ID Reporting Name Available Separately? Always Performed?*
GTFG Glucose Fasting N Y
GT1G Glucose 1 Hour N Y
GT2G Glucose 2 Hour N Y

*The tolerance test is canceled if the patient vomits during the procedure.

Specimen Requirements

Patient Preparation

  • An overnight fast is required. The patient's last meal should be eaten 10-12 hours before specimen collection. During the overnight fast, only moderate quantities of water may be taken. Other beverages and caffeine-containing liquids, such as coffee, must be omitted. Avoid chewing gum, mints, candies, or tobacco products. Avoid even mild exercise during the fast. Over-the-counter drugs should be avoided when possible. Prescription medications critical to health maintenance should be taken. 
  • A normal diet should be taken for three days before the overnight fast. No formal diet is recommended unless it is estimated that less than 150 grams of carbohydrates per day has been consumed. For inpatients, it is the responsibility of the nursing staff to ensure that the patient is fasting when appropriate. 
Container Type:

Optimal: Mint

 

Acceptable: Gold or Red

 
Optimal Collection Volume: 

4.5mL; full tube
Minimum Volume:

1 mL whole blood
Collection Instructions:
  1. Gently invert the sample 5-6 times after collection.
  2. After obtaining a fasting specimen, give the patient a 75 g dose of glucose beverage, noting the time of ingestion (the patient must drink the entire beverage within five minutes).
  3. Draw specimens at 1 and 2 hours after ingestion of the glucose beverage. Accurate timing is essential.
  4. Label specimens with corresponding draw time and interval.
  5. Indicate if the patient is pregnant on the request form.
Specimen Transport:

Refrigerate
Processing Instructions: 
  1. If serum, allow the specimen to clot for 30 minutes.
  2. Centrifuge specimen within 2 hours of collection.
  3. After centrifugation, specimen tubes without a gel barrier should have the serum or plasma aliquoted to a false bottom container.
  4. Keep the serum or plasma refrigerated until testing can be performed.

Specimen Stability

Specimen Type Temperature Time
Serum* Refrigerated 3 days
Room Temperature 8 hours

*Note: Heparinized plasma in gel separator tubes is less stable than serum and is only suitable for add-on testing up to 2 days following sample collection.

Specimen Rejection Criteria

Hemolysis Mild OK; Moderate OK; Gross Reject
Lipemia Mild OK; Moderate OK; Gross Reject
Icterus Mild OK; Moderate OK; Gross Reject
Other Quantity not sufficient

Methodology

Roche Cobas - Enzymatic with hexokinase

Reference Ranges

The diagnosis of Gestational Diabetes Mellitus (GDM) is made when any of the following glucose values exceed its reference range.

 

Specimen Reference Range and Reporting Units
Glucose Fasting 70-91 mg/dL
Glucose 1 hour 70-179 mg/dL
Glucose 2 hour 70-152 mg/dL

Day(s) Performed

Monday through Friday, by appointment only

Expected TAT

Same day

Performing Laboratory

Bronson Laboratory, Chemistry - Kalamazoo, Battle Creek, Paw Paw, South Haven

Sample Retention Time

7 days

CPT Code

  • 82951 - Glucose tolerance, 3 specimens (includes glucose)

LOINC Code

N/A