What is a Prolonged Glucose Tolerance Test?
It’s basically the same test pregnant women have to check for diabetes during pregnancy, except it lasts for longer. In my case, my consultant ordered it to confirm his diagnosis of Insulin Resistance and to rule out Reactive Hypoglycaemia. Insulin and cortisol are linked together, so because I lack cortisol because of my Secondary Adrenal Insufficiency, it’s unsurprising that there are bits of the puzzle missing elsewhere. Insulin Resistance is where glucose stays in the blood stream rather than passing into cells with the help of insulin, meaning the body has to overproduce insulin to get it to convert. The way my consultant explained it is it’s a bit like insulin and glucose coming across a stuck door, pushing and heaving and then calling for more backup insulin until everything crashes through. Reactive Hypoglycaemia is where blood sugars drop to a dangerous level after eating.
What does the test involve?
The Prolonged Glucose Tolerance Test lasts just over 4 hours. It’s supervised by an endocrine nurse, so you have to spend a morning starting from 8am in hospital, and are given a patient bed. A cannula is inserted first, giving access to a vein and avoiding having to have a needle for every test, and a baseline sample of blood is taken measuring insulin and glucose. The nurse also does a finger prick blood glucose test at the same time. After that, you’re given a sugary glucose drink, which doesn’t really taste of anything and is a bit thick to drink. The nurse takes blood samples every half an hour for 4 hours, and another finger prick test at the half way point. At the end of the test, you’re given something to eat before leaving and can go back to your normal routine afterwards.
How does it work?
The test tracks how the body responds to glucose over a period of time and how the relationship between insulin and glucose works in the body during that time.
What preparation do you have to do beforehand?
You’re not allowed to eat for 8 hours before the test, and can only drink water during this time. You should drink lots of fluids in the days leading up to the test and can still take all your normal medications. You don’t have to be on your baseline dose eg if you’re tapering from stress dosing, but the test won’t be done if you’re feeling ill. Once the test is over, you can eat again like normal.
What does the test feel like?
The cannula being inserted is only a little bit worse than the normal blood test ‘sharp scratch’. The drink doesn’t really taste of anything and it doesn’t make you feel any different afterwards. I had a nap in between most of the blood draws, but this was more to do with the fact that I hadn’t eaten rather than the test itself. Take a book! I slept for the rest of the afternoon and felt a bit ‘off’ because of not being able to eat, so ate lots of carbs afterwards.
What do the results show?
I’m not expecting the results to show anything I didn’t already know as this test was to confirm the Insulin Resistance diagnosis I’ve already been given and to completely rule out Reactive Hypoglycaemia. It does mean that I can start taking a tablet called Metformin, which is used to level out blood sugar levels through the day. Starting the medication before the test would have skewed the results.