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Test Code GTT3 Glucose Tolerance Test (3 Hour), Plasma or Serum and Urine

Specimen Requirements

Plasma or serum and urine specimen are required for this test.

 

Patient Preparation
1. Patient should be on at least a 150 g carbohydrate diet for 3 days prior to testing and should be off all hypoglycemic drugs, such as birth control pills, aspirin, diuretics, ethanol, and steroids.
2. Patient should not smoke, eat, drink coffee, or exercise 10 to 16 hours prior to and during test.
3. Patient may have water during test.

 

Specimen Collection
Plasma

Draw blood in a green-top (lithium heparin) tube(s) or a plasma gel tube(s) from a fasting patient (10-16 hour preferred). Spin down (maximum:  2 hours) and send 1 mL of lithium heparin plasma as follows:
1. Fasting glucose is drawn in a green-top (lithium heparin) tube(s).
2. If your patient is sent to the laboratory, we will assure that this fasting level is <200 mg/dL prior to administering a 100 g dose of glucola. If the fasting specimen is run and if >200 mg/dL, physician is consulted prior to proceeding with the testing.
3. Dose the patient with 100 g of glucola. Instruct patient to drink whole amount within 5 minutes, if possible.
4. Green-top (lithium heparin) tube(s) is drawn for each specimen (fasting, 1/2 hour, 1 hour, 2 hour, and 3 hour).

5. Send all 5 specimens refrigerated in separate vials.
Note:  1. If glucose is the only test ordered, draw specimens in grey-top (potassium oxalate/sodium fluoride) tube(s) to ensure integrity.

2. Indicate corresponding draw time and plasma on request form.

3. Label specimens appropriately (corresponding draw time and as plasma).

 

Serum

Draw blood in a plain, red-top tube(s) or a serum gel tube(s) from a fasting patient (10-16 hour preferred). Spin down (maximum:  2 hours) and send 1 mL of serum as follows:
1. Fasting glucose is drawn in a serum gel tube(s).
2. If your patient is sent to the laboratory, we will assure that this fasting level is <200 mg/dL prior to administering a 100 g dose of glucola. If the fasting specimen is run and if >200 mg/dL, physician is consulted prior to proceeding with the testing.
3. Dose the patient with 100 g of glucola. Instruct patient to drink whole amount within 5 minutes, if possible.
4. Serum gel tube(s) is drawn for each specimen (fasting, 1/2 hour, 1 hour, 2 hour, and 3 hour).

5. Send all 5 specimens refrigerated in separate vials.
Note:  1. Indicate corresponding draw time and serum on request form.

2. Label specimens appropriately (corresponding draw time and as serum).

 

Urine

1 mL from a random urine collection in a plastic, screw-capped urine container supplied for each timed specimen. Send specimen refrigerated.

Note:  1. Collection date and time are required on request form for processing.
2. Indicate corresponding collection time and urine on request form.

3. Label specimens appropriately (corresponding collection time and as urine).

Performing Laboratory

Conway Regional Clinical Laboratory Services

Reference Values

See report.

Critical values (automatic call-back):  <40 mg/dL or >450 mg/dL

Note:  Glycolysis due to failure to refrigerate specimen or to send it to the laboratory immediately may result in false-negative results.

Methodology

Hexokinase, Ultraviolet

Day(s) Test Set Up

Monday through Sunday

Available STAT

Test Classification and CPT Coding

81003 - each urine measurement

82951 - 3 specimens

82952 - each additional specimen