What is the role of an oral glucose tolerance test in the workup of pediatric type 1 diabetes mellitus (DM)?

Updated: Mar 23, 2021
  • Author: William H Lamb, MD, MBBS, FRCP(Edin), FRCP, FRCPCH; Chief Editor: Sasigarn A Bowden, MD  more...
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Although unnecessary in the diagnosis of type 1 diabetes mellitus, an oral glucose tolerance test (OGTT) can exclude the diagnosis of diabetes when hyperglycemia or glycosuria are recognized in the absence of typical causes (eg, intercurrent illness, steroid therapy) or when the patient's condition includes renal glucosuria (see Glucose).

Obtain a fasting blood sugar level, then administer an oral glucose load (2 g/kg for children aged < 3 y, 1.75 g/kg for children aged 3-10 y [max 50 g], or 75 g for children aged >10 y). Check the blood glucose concentration again after 2 hours. A fasting whole-blood glucose level higher than 120 mg/dL (6.7 mmol/L) or a 2-hour value higher than 200 mg/dL (11 mmol/L) indicates diabetes. However, mild elevations may not indicate diabetes when the patient has no symptoms and no diabetes-related antibodies.

A modified OGTT can also be used to identify cases of MODY (which often present as type 1 diabetes) if, in addition to blood glucose levels, insulin or c-peptide (insulin precursor) levels are measured at fasting, 30 minutes, and 2 hours. Individuals with type 1 diabetes mellitus cannot produce more than tiny amounts of insulin. People with MODY or type 2 diabetes mellitus show variable and substantial insulin production in the presence of hyperglycemia.

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