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Test Code GTT GLUCOSE TOLERANCE, DIABETES MEL

Important Note

  1. Patients are required to have an appointment for Glucose Tolerance Testing and should contact the Logan Health Medical Center Laboratory at 406-752-1737 to schedule appointment.
  2. Medical Offices should provide each patient with the Patient Information Sheet for Glucose Tolerance Testing.
  3. Medical Office Clinical Staff members should review the Medical Practice Protocol for patient GTT.
  4. Offices should contact the Laboratory for drawing instructions if specimens are to be drawn at the Physician’s Office.

Methodology

Colorimetric

 

Useful for evaluating glucose response to an oral glucose solution in order to support or rule out a diagnosis of diabetes mellitus.

Specimen Requirements

Patient Preparation:

  1. Patient must be on a normal diet for 3 days prior to testing, and be fasting for at least 8 hours prior to test.
  2. This test should not be performed on hospitalized, acutely ill, or inactive patients.
  3. This test is not recommended for pediatric patients.

 

Procedure:

  1. Draw fasting specimen before administration of glucose.
  2. Administer 75 g glucose solution orally to nonpregnant adults. Call Logan Health Medical Center Laboratory at 406-752-1737 for adjusted dosages for children (<95 lbs).
  3. Two hours after ingestion of glucose, draw a second blood specimen.

 

Specimen Collection:

Submit only 1 of the following specimens for each draw time:

 

Preferred:

Plasma

Container/Tube:  Grey-top (potassium oxalate/sodium fluoride) tube(s)

Specimen Volume: 1 mL (minimum volume: 0.5 mL) of plasma-Grossly hemolyzed specimen is not acceptable.

Collection Instructions: Spin down within 30 minutes of draw.

 

Note:

  1. Grey-top tube is stable for 24 hours after drawing specimen.
  2. Label specimens appropriately (time of draw and as plasma).

 

Alternate:

Serum

Serum Gel Tube

Container/Tube: Serum gel tube(s)
Specimen Volume: 1 mL (minimum volume: 0.5 mL) of serum-Grossly hemolyzed specimen is not acceptable.

Collection Instructions: Spin down within 30 minutes of draw.

Note: Label specimens appropriately (time of draw and as serum).

 

Alternate:

Plasma

Container/Tube: Green-top (lithium heparin) tube(s)

Specimen Volume: 1 mL (minimum volume: 0.5 mL) of serum-Grossly hemolyzed specimen is not acceptable.

Collection Instructions: Spin down within 30 minutes of draw.

Note: Label specimens appropriately (time of draw and as plasma).

 

 

Day(s) Test Set Up

Monday through Sunday

Reference Values

TRUE “NORMAL” GLUCOSE

Fasting: <100 mg/dL

2 hours: <140 mg/dL

 

IMPAIRED GLUCOSE TOLERANCE

Fasting: 110-125 mg/dL

2 hours: 140-199 mg/dL

 

DIABETES

Fasting: ≥126 mg/dL

2 hours: ≥200 mg/dL

 

Critical values (automatic call-back): <50 mg/dL or >500 mg/dL

 

Diagnosis of diabetes mellitus requires that 1 of the following criteria are met:

  1. Casual plasma glucose ≥200 mg/dL with classic symptoms of diabetes (polydipsia, polyuria, polyphagia, and weight loss). 
  2. Fasting glucose ≥126 mg/dL
  3. 2-hour glucose ≥200 mg/dL during an oral glucose tolerance test (GTT).

 

Abnormal results must be confirmed by repeat testing, on a subsequent day, preferably by the same method.

Performing Laboratory

Logan Health Medical Center-Chemistry

Test Classification and CPT Coding

82947-Glucose

82950-Post glucose dose

Specimen Transport Temperature

Refrigerate

Special Instructions