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Test Code OGT or LAB824 Glucose Tolerance, Non-Pregnant, Serum or Plasma

Important Note

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

Please note the patient preparation steps required in the Specimen Requirements section below.

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

Specimen Requirements

Patient Preparation:
  • An overnight fast is required. 
    • The last meal should be eaten before the test no sooner than 10-12 hours.
    • Moderate quantities of water may be taken.
  • During the fast, avoid:
    • Beverages such as soda or coffee.
    • Chewing gum, hard candies, or tobacco products.
    • Exercise
    • Over-the-counter drugs
      • Prescription medications critical to health maintenance should be taken.
  • A regular diet should be consumed for three days before the overnight fast.
    • Low-carb diets - Consult a doctor before scheduling the test.
  • Patients < 12 years of age
    • Include the patient's weight on the request form so that the proper glucose dosage is administered.
Container Type:

Optimal: Gold or Mint

Acceptable: Red or Green
Optimal Collection Volume: 

4.5mL; full tube
Minimum Volume:

1 mL whole blood
Collection Instructions:
  1. This test includes two specimens.
    • Fasting
    • 120 minutes (2 hours)
  2. Obtain the fasting specimen.
  3. Administer a 75 g dose of glucose. Note the time of ingestion.
    • The patient must drink the entire dose of glucose within 5 minutes.
  4. Draw the 2-hour specimen at the appropriate interval of time. 
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

Patient vomits

Patient not fasting

Useful For

Used to make a diagnosis of diabetes mellitus.

Methodology

Roche Cobas - Enzymatic with hexokinase

Reference Ranges

Specimen

Reference Range and Reporting Units

Normal

Impaired

Diabetic

Fasting

70-99 mg/dL

100-125 mg/dL

> 125 mg/dL

2-hour

65-139 mg/dL

140-199 mg/dL

> 199 mg/dL

Day(s) Performed

Monday through Saturday

Expected TAT

Same day

Performing Laboratory

Bronson Laboratory, Chemistry - Kalamazoo and Battle Creek

Sample Retention Time

7 days

CPT Code

  • Glucose quantitative - 82947
  • Glucose post-dose - 82950