GTT and fasting BG test

[brianb]

Just something going through my mind from another thread.

What does a fasting BG test tell you that a GTT does not??

Is it posssible to have a "normal" GTT and still have a high Fasting Blood glucose?? Ie my fasting levels on diagnosis were 8.9 on 2 tests a week apart BUT normal GTT. WHAT does this mean?

I know that the GTT can show you are pre diabetic but you would think that as my fasting BG were 8.9 then the GTT would be high as well.

I have to say i do spike to about 10 or 11 @ 1 hour after meals but by 2 hours can be back to 5.5 ish

Just another one of those things going round me head, maybe someone knows the answer.

Thanks

Brian

 

[sugarless sue]

A fasting blood test could be skewed by the 'Dawn phenomenon' especially if you have been rushing about to get to the surgery for your test.A GTT is a measured amount which is then measured after 2 hours to see how well your pancreas has coped with metabolising the glucose.

 

[Dennis]

Hi Brian,
A fasting glucose test and a GTT are not really related because they are testing different things. A fasting test tells what your BG level is at it's lowest point in the day, so it is a snapshot at one moment in time. A fasting level of below 6.1 mmol/l is regarded as non-diabetic, between 6.1 and 7.0 is borderline ("impaired fasting glycaemia"), and a fasting level above 7.0 mmol/l indicates diabetes.

A GTT is used to measure how quickly a measured amount of glucose is cleared from your blood. It gives the tester an idea of how much insulin you can produce in response to the glucose and also an indication of what degree of insulin resistance you have. A blood test is done at the start to determine the start point, then at 2 hours after you have drunk the glucose solution. Sometimes other samples may be taken between these, depending on what the tester is looking for.

 

[brianb]

HI
Thanks for the replys.

Dennis

So in my case where i had 2 Fasting BG of 8.9 which makes me diabetic without question
And
a normal GTT after 2 hours means that yes im diabetic BUT i can produce enough insulin to cope with a GTT, Is that correct? If so why if i can produce enough insulin in a GTT can i have two fasting BG of 8.9, thats the bit i cant understand.

Sorry if that sounds thick

Brian

 

[Dennis]

Hi Brian,

Please bear in mind that I am not a medic, but to me the logical conclusion from your results is that your pancreas is able to produce sufficient insulin to deal with an increase (as the GTT would have given you, or as a meal would do) but your system is not recognising that your base level is already too high. You seem to have a normal insulin response to a raise in BG from food but not to your high base level of BG. I suspect that if you were to go on a crash very low carb diet for a week, you would see your base-line BG drop to a more normal level, which hopefully you would then be able to maintain once back on your normal diet.