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Test Code LAB1842 Glucose, Gestational Diabetes Tolerance, 3 Hour

Useful For

Aiding in the diagnosis of diabetes mellitus

Methodology

Enzymatic reference method with hexokinase

Performing Laboratory

Bozeman Health Laboratory Services

Specimen Requirements

Patient Preparation:

  1. Patient should maintain a normal carbohydrate diet (at least 300 g of carbohydrates per day) for 3 days prior to test. 
  2. Patient should follow physicians instructions regarding fast.
  3. Patient must not eat or drink during testing. Ice chips may be given to moisten mouth.

Performance of Test:

  1. Draw a fasting blood specimen.
  2. Have adult patient drink entire 100 g of glucose tolerance beverage.
  3. Ingestion should be completed within 10 minutes. Timing starts at this point.
  4. If patients vomits, cancel test and reschedule.
  5. Exactly 1-hour, 2-hours, and 3-hours after ingestion of glucose beverage, draw blood specimens.

Specimen Collection:

Specimen Type: Plasma or serum
Container/Tube: Light-green top (lithium heparin gel), red top or gold top
Specimen Volume: 1 mL
Specimen Minimum Volume: 0.5 mL

Collection Instructions: Label specimen with time of draw.  Complete clot formation should take place before centrifugation.  Spin down and separate cells within half an hour of collection.  

Additional Information

  • Includes fasting, 1-hour, 2-hour, and 3-hour plasma tests for glucose

Specimen Transport Temperature

Ambient <8 hours/Refrigerated >8 hours

Specimen Stability

Specimen Type Temperature Time
Plasma or serum Ambient 8 hours
  Refrigerated 3 days

Note: Glycolysis decreases serum glucose by approximately 5% to 7% per hour in normal, uncentrifuged, coagulated blood at ambient temperature.

Reference Values

Fasting Glucose: 70-95 mg/dL

1-hour Glucose: 70-180 mg/dL

2-hour Glucose: 70-155 mg/dL

3-hour Glucose: 70-140 mg/dL

 

Critical values (automatic call-back): ≤50 mg/dL or ≥400 mg/dL

Day(s) Test Set Up

Monday through Sunday

Test Classification and CPT Coding

82952