Glucose Tolerance Test, 4 Specimens
Also known as: 3 HR GTT (4 Specimens), 3 HR Glucose Tolerance, Non-pregnant, Glucose Tolerance 3 HR, Non-pregnant
Use
This test evaluates how the body processes a glucose load over a three‑hour period. A baseline (fasting) blood specimen is obtained followed by glucose ingestion and three additional timed collections to assess glucose tolerance. It is commonly used for diagnosis of diabetes and prediabetes according to ADA criteria: fasting ≥126 mg/dL or 2‑hour ≥200 mg/dL indicates diabetes; children may be dosed per weight (1.75 g/kg up to 75 g) with similar thresholds. It also informs detection of insulin resistance, metabolic syndrome, and other carbohydrate metabolic disorders.
Special Instructions
Patient must fast for 10‑12 hours before the fasting draw. Immediately after the fasting specimen, the patient ingests a 75 g glucose load. Subsequent draws occur at 1, 2, and 3 hours. Patients must remain in the laboratory during the testing period. Three days prior, patients should consume a diet containing at least 150 g of carbohydrates daily and may need to discontinue nonessential medications affecting glucose metabolism, per provider guidance.
Limitations
Glucose levels may be artifactually low if the sample is left unprocessed for extended periods. Results may be delayed by weather, holidays, or laboratory logistics. Timing deviations or non‑fasting status may invalidate interpretation. For children, glucose dosing is weight‑based up to maximum. Also note that without careful timing and pre‑test dietary preparation, results may not accurately reflect patient’s post‑challenge glucose tolerance.
Methodology
Automated Analyzer (Clinical Chemistry)
Biomarkers
Result Turnaround Time
1-2 days
Related Documents
For more information, please review the documents below
Specimen
Plasma
Volume
Not provided
Minimum Volume
Not provided
Collection Instructions
Four venous blood draws (fasting, then at 1 h, 2 h, 3 h) after ingestion of 75 g glucose
Patient Preparation
Fasting 10‑12 hours required; three days prior ingest ≥150 g carbohydrates; discontinue nonessential meds per provider
Other tests from different labs that may be relevant