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Glucose Tolerance Test
Related Subjects: |Ferritin |CEA |ESR |CRP |ALP |LDH |HbA1c |Alpha Fetoprotein |Anti-Hu ab |Biochemical Lab values
📖 About
- Glucose Tolerance Test (GTT) assesses how the body handles a glucose load.
- Physiology: Glucose should suppress Growth Hormone (GH) and stimulate pancreatic insulin release.
🎯 Indications
- Diagnosis of Diabetes Mellitus.
- Diagnosis of Acromegaly (failure of GH suppression).
⚠️ Cautions
- Fasting for at least 8 hours.
- No smoking or caffeine prior to the test.
- Patient must remain seated and rested during the procedure.
🧪 Method
- Administer 75 g oral glucose (≈ 388 mL Lucozade).
- Take fasting blood glucose, then repeat at 2 hours.
- For suspected acromegaly → measure GH at baseline and 2 hours.
🔍 Investigations & Interpretation
- No Diabetes: FBG < 6 mmol/L, 2-hr glucose < 7.8 mmol/L.
- Prediabetes (Impaired Glucose Tolerance):
- FBG: 6.1–6.9 mmol/L
- 2-hr glucose: 7.8–11.0 mmol/L
- Diabetes Mellitus:
- FBG ≥ 7.0 mmol/L
- 2-hr glucose ≥ 11.1 mmol/L
- HbA1c ≥ 6.5%: Also diagnostic of Type 2 Diabetes (if confirmed on repeat test).
- Acromegaly: Failure of GH to suppress < 2 mIU/L after glucose load.
💡 Clinical Pearls
🔑 The GTT is the gold standard for diagnosing gestational diabetes.
📊 Always use plasma glucose (not capillary finger-prick) for formal diagnosis.
🧬 In acromegaly, paradoxical rise in GH after glucose can sometimes be seen.
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