Test Code Billings Clinic: 4665 Glucose Tolerance Test (GTT), 2 Hour, Plasma or Serum
Performing Laboratory
Billings Clinic Laboratory: Chemistry
Useful For
- Screen for type 2 diabetes
- Diagnose gestational diabetes
Methodology
Hexokinase
Specimen Requirements
Consult Billings Clinic Laboratory at 866-232-2522 for pediatric doses.
Serum or plasma should be physically separated from cells as soon as possible with a maximum limit of two hours from the time of collection.
- Draw blood in a green-top (lithium heparin) tube(s) or a red-top tube (serum) from a fasting patient.
- Have adult patient drink entire glucose tolerance beverage supplied. Ingestion should be completed within 10 minutes. The timing starts at this point.
- Draw specimen as above 2 hours after ingestion of the dose.
- During time of draw, patient must not eat or drink, with the exception of plain water.
- They may be given ice chips or plain water to moisten mouth.
- Spin down each specimen, separate plasma or serum from cells as soon as possible after draw, and send 1 mL of heparinized plasma or serum.
- It is suggested that patient follow a special high carbohydrate (150-300 g) diet for 3 days prior to this test unless otherwise directed by the physician.
- Glucose solution will not be given to patients with fasting glucose = 150 mg/dL without notification and consent of physician.
- Vomiting negates test.
- Label specimens appropriately (timed interval).
DO NOT FREEZE
Storage/Stability
Type | Temperature | Time |
Plasma, Serum | Refrigerated | 3 days |
Ambient | 8 hours |
Reject Due To
- Specimens received frozen
- Gross hemolysis
Reference Values
Varies
Day(s) Test Set Up
Daily
Test Classification and CPT Coding
82950 x 2 - Glucose; quantitative, post glucose dose (includes glucose)
LOINC Code Information
Reporting Name | LOINC Code |
Glucose, Fasting | 2345-7 |
GTT, 2 Hour | 2345-7 |