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Glucose tolerance test (2hrs)

Test Overview

The 2-Hour Glucose Tolerance Test (GTT) is a diagnostic test used to assess how the body processes glucose over time. It is commonly used to screen for diabetes, prediabetes, and gestational diabetes by measuring blood sugar levels before and after consuming a glucose solution. This test evaluates the body’s ability to regulate glucose and helps detect impaired glucose metabolism.

Test Types

  • Fasting Blood Glucose Test (FBG): Measures baseline blood sugar before glucose intake.
  • 2-Hour Glucose Tolerance Test (GTT): Measures glucose levels before and 2 hours after consuming a glucose solution.
  • Extended Glucose Tolerance Test: May include additional readings at 30 minutes, 1 hour, and 2 hours for detailed analysis.

Glucose Tolerance Test (2-Hour) Results & Ranges

Test Component: Normal Range: Prediabetes: Diabetes:
Fasting Glucose (Before Test) 70–99 mg/dL 100–125 mg/dL ≥126 mg/dL
Glucose Level (2 Hours Post-Glucose Load) <140 mg/dL 140–199 mg/dL ≥200 mg/dL
  • Normal: The body effectively processes glucose, returning to a healthy range within 2 hours.
  • Prediabetes: Impaired glucose tolerance (IGT), indicating a higher risk of developing diabetes.
  • Diabetes: Blood sugar remains elevated, confirming diabetes.

 

Expected Turnaround Time

  • Results Available: Within 24 hours

Specimen Requirements

  • Sample Type: Blood sample (venipuncture)
  • Fasting Required? Yes, 8–12 hours before the test
  • Container: Serum separator tube (SST) or fluoride (gray-top) tube

Collection Instructions

  1. Fast for 8–12 hours before the test (water is allowed).
  2. Baseline Blood Draw: A fasting glucose level is measured.
  3. Glucose Load: The patient consumes a 75g glucose solution within 5 minutes.
  4. Wait Period: Rest without eating, drinking, or exercising for 2 hours.
  5. Final Blood Draw: A second sample is taken exactly 2 hours after consuming the glucose.
  • Storage: Keep samples refrigerated if delayed beyond 1 hour.

Test Details

  • Clinical Use: Diagnoses diabetes and prediabetes in non-pregnant individuals. Identifies gestational diabetes in pregnant women (separate criteria apply). Assesses glucose metabolism disorders.
  • Limitations: Certain medications (e.g., steroids, diuretics) can affect results. Stress, illness, or improper fasting can lead to false readings. Not recommended for individuals with known diabetes (fasting glucose >200 mg/dL).

The 2-Hour Glucose Tolerance Test provides a detailed assessment of blood sugar regulation, aiding in the early detection and management of diabetes and metabolic disorders.