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Test Code BLOD0788 Glucose Tolerance 3 Hour

Important Note

Fasting specimen required.  Patient should follow physicians instructions regarding fast.

Useful For

Aiding in the diagnosis of diabetes mellitus


Hexokinase/Ultraviolet (UV)/Bichromatic End point

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 75 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, gold top, or grey top (potassium oxalate/sodium fluoride)
Specimen Volume: 1 mL
Specimen Minimum Volume: 0.5 mL

Collection Instructions:

1. If there is a delay in transport of >8 hours, refrigerate specimen, and send specimen refrigerated.

2. Label specimen as plasma or serum and with time of draw.

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
Heparinized plasma or serum Ambient 8 hours

3 days

  Frozen 1 month
Sodium Fluoride plasma Ambient 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: 70-99 mg/dL

1-hour Glucose: 70-139 mg/dL

2-hour Glucose: 70-139 mg/dL

3-hour Glucose: 70-139 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

82951-Glucose tolerance test, 3 specimens and dose

82952-Glucose, each additional beyond 3