Prolonged oral glucose tolerance test
Why is this done?
This can be done to stimulate the pancreas to see if there is a dip in blood glucose after a glucose challenge. This test may take up to 5 hours. There is some evidence that the mixed meal test may be better.
Prerequisites
- The person should be on a normal carbohydrate diet for the preceding 3 days.
- It must be done with caution or avoided in those with ischaemic heart disease or seizures.
- The person must fast from 12 midnight the previous night
- water is permitted
- Please avoid alcohol the previous evening/ night
Requirements
- 75 g anhydrous glucose.
- Fluoride oxalate tubes for glucose.
- EDTA (purple) tubes
- Clotted red or yellow tubes
- 20g i.v. cannula.
- Saline flush.
- Patient arrives fasting at 8 AM
- Patient should not exercise or smoke during the test
- Please inform laboratory that sample for C peptide and insulin may arrive for urgent processing.
To be alert for
Some patients may have transient hypoglycemia like symptoms. They usually do not require treatment and resolve spontaneously
| Bloods | Procedure | Comments | |
| – 15 min | Glucose
c peptide Insulin Gut hormones plasma metanephrines |
Insert canula
Prepare glucose solution with 75 grams of glucose in water |
Table |
| T +0 min | Patient drinks glucose solution in
10 min |
Table | |
| T + 1 hour | Glucose | Finger prick test
Glucose _____ |
|
| T + 2 hours | Glucose | Ask patient for any symptoms
__________________ If patient has symptoms collect blood for Insulin and c peptide – keep on ice |
Finger prick test
Glucose _____ |
| T + 3 Hours | Glucose | Ask patient for any symptoms
__________________ If patient has symptoms collect blood for Insulin and c peptide – keep on ice |
Finger prick test
Glucose _____ |
| T + 4 hours | Glucose | Ask patient for any symptoms
__________________ If patient has symptoms collect blood for Insulin and c peptide – keep on ice |
Finger prick test
Glucose _____ |
| T+ 5 hours | Glucose | Ask patient for any symptoms
__________________ If patient has symptoms collect blood for Insulin and c peptide – keep on ice |
Finger prick test
Glucose _____ |
| T + 5.5 hours | Table | Ask patient for any symptoms
__________________ If patient has no symptoms patient can be discharged |
If samples need collection for insulin / C peptide ( if patient has symptoms, The sample must be transported to lab urgently
INTERPRETATION
Symptoms consistent with hypoglycaemia in the presence of a low glucose
(usually below 3.0 mmol/L), would be sufficient to diagnose reactive hypoglycemia
Ajith George