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Frequent Responder
Total Posts: 244
Registered on: ‎07-22-2011

Why is Blood Glucose Test done fasting?

Okay, I'm a newbie here.  So bear with me.  It seems to me like the measurements that doctors are looking at is the HAC1.  And this measurement (in laymans terms, I know this is not 100% accurate), is a 120 day look at your blood glucose levels (or plasma, etc).  So, while we are all trying to monitor and control our blood glucose by monitering it as we do, we are doing so in an effort to either lower or maintain a "healthy" HAC1.  Since the HAC1 test measures a 120 look, it seems to me like this blood test wouldn't matter if it were done fasting or not.  One meal is not going to have even a miniscule impact on your HAC1 score.  So, why do we need to fast when we have this test done along with our blood glucose test?  The blood glucose test is just a snapshot of recent blood glucose measurements, and the goal is really the HAC1.  So fasting for these tests does not make "common" sense to me.
AC1 - Diagnosed 10/6/10 - 10.8
1/26/11 - 6.8
7/8/11 - 7.5
1/14/12 - 5.6
Next bloodwork 3/12, for LDL only
Triglycerides 134 as of 1/14/12.  Metformin 2 x 850 mg.  Glipizide 1 x 10 mg, twice daily.  The glip I have down-dosed myself. 
Frequent Responder
Total Posts: 61
Registered on: ‎03-29-2011

Why is Blood Glucose Test done fasting?

I am fairly new also but I think I can answer your question.  The HA1C doesn't have to be a fasting test but they usually do it the same time as the fasting glucose so you only have to be stuck once with the needle.  You can not achieve a "healthy A1C" unless you get the daily blood sugars under control.  So testing daily is very important.  Maybe one meal isn't going to effect the A1C but if you have too many meals that are high they will.
"The joy of living life is his who has the heart to demand it.Theodore Roosevelt

Diagnosed Type 2 on 3/29/2011 with a  A1C of 12.9
3/2012 A1C 6.0
Trusted Contributor
Total Posts: 11,135
Registered on: ‎11-28-2009

Why is Blood Glucose Test done fasting?

An A1c test can be done anytime. If fasting is required when it is done, it is because of other tests that are being done at the same time--which might be fasting blood glucose, or a lipid panel, or other tests.
Morris

Diagnosed Type 2, with an A1c of 11.4 in 2003; averaging a 5.0 A1c since then with diet, exercise and Glipizide XL + meds for blood pressure and cholesterol. 
A bit dated, but scroll down on this page if you want to know more ...


Frequent Responder
Total Posts: 244
Registered on: ‎07-22-2011

Why is Blood Glucose Test done fasting?

Morris, thanks.  I think my question is simply, why does the blood glucose test need to be done fasting?  We as type 2 diabetics take our blood glucose readings before we eat, after we eat, when we wake up (not necessarily 12 hours after we go to bed...).  I've read here that some people's blood glucose is high when they first wake up in the morning and goes down after they have their first meal...

So, what is the "magic" of having to test the blood glucose while fasting, particularly if the HAC1 test is really the "litmus" test....
AC1 - Diagnosed 10/6/10 - 10.8
1/26/11 - 6.8
7/8/11 - 7.5
1/14/12 - 5.6
Next bloodwork 3/12, for LDL only
Triglycerides 134 as of 1/14/12.  Metformin 2 x 850 mg.  Glipizide 1 x 10 mg, twice daily.  The glip I have down-dosed myself. 
Frequent Responder
Total Posts: 619
Registered on: ‎11-03-2009

Why is Blood Glucose Test done fasting?

Hi Tony
Good questions. glad you are actively participating!  I know how puzzling this all is at first. I'd suggest that you look at the tests with a bit different focus -
- the A1c tells us how we are doing over time, and our daily Fasting (FBG), pre-meal, and post-meal (PP) testing results are immediate info we use to determine how we are doing (very short term).
I/we want to know what the effects are of what I've eaten, so I can adjust my food intake to maximize keeping my BG#'s in target range:
 - the day before/night before foods show up in my fasting BG # (and I believe the 'magic' # of hours is 8, not 12),
-testing before a meal,(think baseline),  then either 1 hr or 2 hr after (PP= post prandial) is done to find out the effects of whatever was eaten.
This frequency of testing doesn't have to be life-time. Many people here have built up a personal knowledge base on how their body reacts to foods - yes there are generalities, but each of us has different reactions to different foods.
Some excellent info I suggest you read are on Alan S's and on Lizzylou's profile, Morris is a hiking 'D' encyclopaedia (meant in the nicest way) Hope this helps.
Sorry I am so wordy, it's an occupational hazard,  Vicki
Live (to the max), Love (and hopefully be loved), Laugh (at every opportunity),
Eat (healthily), Pray (if it suits you),
Love (yourself enough - to put your  health first).
Diagnosed 2001,  I am a work in progress = progressing to not let 'D' control me - with the help of my 'D' family here.
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Registered on: ‎10-31-2009

Why is Blood Glucose Test done fasting?

 



Trisha

IDDM (Type 1 Autoimmune) 30+ years ~ Currently using MDI & Minimed CGM ~
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Frequent Responder
Total Posts: 244
Registered on: ‎07-22-2011

Why is Blood Glucose Test done fasting?

Vicki, thanks....  BTW, when I go to the lab for my blood testing, they always ask "have you been fasting for 12 hours".  So, if Type 2 diabetics are liable to have "dawn phenomenon", and to me it makes sense that most people would want to do their fasting lab work done in the am (after  you wake up and before breakfast), then it still seems to me like fasting Blood Glucose is not going to give the doc much info.  In fact, it is very possible that fasting blood work (based upon what I have read here in the past two days) may indeed give the doctor a false reading on what your blood glucose levels really are....???????
AC1 - Diagnosed 10/6/10 - 10.8
1/26/11 - 6.8
7/8/11 - 7.5
1/14/12 - 5.6
Next bloodwork 3/12, for LDL only
Triglycerides 134 as of 1/14/12.  Metformin 2 x 850 mg.  Glipizide 1 x 10 mg, twice daily.  The glip I have down-dosed myself. 
Total Posts: 14,157
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Registered on: ‎10-31-2009

Why is Blood Glucose Test done fasting?

I think my question is simply, why does the blood glucose test need to be done fasting?

It doesn't.  Usually when they do blood tests they also do a lipid (cholesterol) test, which does have to be done fasting.

Most doctor's realize that the BG reading at that time is after fasting for a period of time and don't really look at it as a "normal" reading.  It's only one reading of many you take on a daily basis.  You could also point it out.

Are you keeping a log of your daily readings (including fasting) to show to the doctor.  Many ask you for one at first.

Have you read the links below:  Testing 101 and All About Carbs?

Lizzy
Knowledge is Power!





Here's some useful links, click on the titles


Testing 101
 
 All About Carbs

Resources For The Un-insured and Discount Medicine and Equipment

LizzyLou Videos



Lizzy's Blog
for lots more  


Frequent Advisor
Total Posts: 589
Registered on: ‎03-17-2011

Why is Blood Glucose Test done fasting?

If the doctor looked at the number and only that number, it would present a problem.  However, in combination with the HbA1c and your own log, (s)he has a lot of information to look at.  It is important for the doctor to see if you are experiencing a liver dump as they may be able to make adjustments or give suggestions to prevent them.  The true goal is to reach good numbers and keep them somewhat level rather than having peaks and valleys in the readings.  Of course, your numbers are going to go up and down, you just don't want major swings.

"No one can make you feel inferior without your consent." -- Eleanor Roosevelt


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Total Posts: 14,157
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Registered on: ‎10-31-2009

Why is Blood Glucose Test done fasting?

 
Knowledge is Power!





Here's some useful links, click on the titles


Testing 101
 
 All About Carbs

Resources For The Un-insured and Discount Medicine and Equipment

LizzyLou Videos



Lizzy's Blog
for lots more