Oral Glucose Tolerance Test (OGTT)
Code:
GTT
Sample Type:
Plasma (Fluoride-oxalate: Grey Top)
Minimum volume: 1 mL
Ref Ranges/Units:
Fasting:
3.0 – 6.0 mmol/L
6.1 – 6.9 mmol/L impaired glucose tolerance (‘pre-diabetic’)
>7.0 mmol/L suggestive of diabetes mellitus
Random:
3.0 – 7.7 mmol/L
7.8 – 11.0 mmol/L impaired glucose tolerance (‘pre-diabetic’)
>11.1 mmol/L suggestive of diabetes mellitus
Results <2.5 or >25 mmol/L (>15 mmol/L if under 16 years) will be phoned to the requesting clinician.
Turnaround:
Same Day (60 minutes from receipt for Urgent Samples).
Stability:
3 days at 15‑25°C
Special Precautions/Comments:
Fluoride-oxalate preservative is required to inhibit glycolysis and prevent falsely low results.
Additional Information:
An Oral Glucose Tolerance Test (OGTT) is a dynamic function test used to assess the regulation of blood glucose levels. It is primarily used in the investigation of gestational diabetes in pregnant women between 24-28 weeks. An OGTT can also be used in the investigation of growth hormone (GH) excess (known as acromegaly). This is because hyperglycaemia usually suppresses GH, but this suppression is not seen in acromegaly.
The relevant local protocol should be followed to ensure the patient is appropriately prepared and the correct samples are collected. In essence, a baseline fasting glucose sample is collected before the patient drinks an anhydrous glucose solution. Approximately 2 hours later, a random plasma glucose is then taken to assess how tightly blood glucose levels are regulated.
South of Tyne & Wear Pathology Centre
