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Fasting glucose vs. A1c - which is more accurate?
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Fasting glucose vs. A1c - which is more accurate?

Hello, I've never been concerned about diabetes before as my fasting blood glucose levels have always been under 100.  However, my last fasting glucose test as well as my husband's were both high (mine 127, his 140).  The doctor had us return for A1c tests which were in the normal range (mine 5.6, his 5.5).  Based on that, the doctor assumed we had eaten something before the fasting test and said, 'see you in 3 months'.  But we didn't eat anything.   I do have doubts about the fasting results because my doctor uses his own lab.  While I know it must be state regulated, we have gotten strange results in the past from this lab.  I told my 80-year Mother about it and she showed me several of her blood test results from years ago that showed her fasting glucose levels were as high as 123, however, her last blood test (and several before that) showed 97.  So...why did she have such high levels in the past and now her readings are normal?  She does not have diabetes.  What would cause high fasting glucose other than diabetes or pre-diabetes?  I'm very confused and would appreciate any insight into this.  Thank you.
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141598_tn?1355675363
"I do have doubts about the fasting results because my doctor uses his own lab.  While I know it must be state regulated, we have gotten strange results in the past from this lab."
The FDA, not the state, requires mfg of glucose test machines to be within specific accuracy. Home meters are plus/minus 20%. Could apply to doctor's equipment too.

"the doctor assumed we had eaten something before the fasting test"
Possible something you ate the night b4 - high starch, high carbs, dairy - affected your liver which in turn produced glucose. This applies to your mother's varied levels. Fasting means NO food NO colored liquids for 8-10 hours prior to testing. Plain water is OK, nothing else. A fasting or an OGTT [oral glucose test] are the first level of tests. When your numbers are high or low the doctor verifies with an A1c.  Bottom line, don't worry unless the A1c is near or above 6%.
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Avatar_f_tn
Thank you, your response was very helpful.  We did eat dinner out the night before...maybe that affected our levels.  We'll check again in 3 months...my husband wants to ask the doctor to send the results out to LabCorp instead of doing them in his own lab.  Hopefully, he'll say yes.  Thanks again.
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Avatar_f_tn
I meant to say....my husband wants to ask the doctor to send our blood samples to LabCorp, not our results.  Sorry about that.
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141598_tn?1355675363
I should have made it clearer that an A1c supersedes the fasting results. With that in mind, I don't understand the urgency [3 months] for retesting when both A1c's are very normal. Normal means an annual A1c test [once a year] if not every two years [No fasting test needed or required during this time period]. I'd question the doc's reason/motive.
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Avatar_f_tn
My doctor will not renew our meds unless we see him every 3 months at which time he usually takes blood (we're both on medications for blood pressure, cholesterol and me for thyroid).  I'm more worried about my husband's glucose because he's very overweight and sedentary while I weigh 112 and have exercised my entire adult life (I'm now 58).  I've been thinking about finding a new doctor...one who sends bloodwork out and does not require us to see him every 3 months.  Thank you again, WaveRider.   You've given me some peace of mind.
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141598_tn?1355675363
OK, you raised some good points why you should seek another doctor not only for a second opinion but also for retesting.

"I do have doubts about the fasting results because my doctor uses his own lab."  
Your husband is "very overweight and sedentary" makes suspect his A1c of 5.5%.

Having thyroid issues may disrupt the insulin production of the pancreas. Have you undergone testing of the pancreas?
1. C-Peptide test is used to help determine how much insulin the pancreas is still producing.

Good luck.
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Avatar_f_tn
I'll check into the C-Peptide test.  Thanks again, WaveRider.
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144586_tn?1284669764
The business about "not renewing meds" unless you see the doctor frequently is not because the doctor wants to milk you of money. It is standard practice, because diabetic medications can cause death of accidents if improperly used. Often, with some diabetic medications, such as Novalog, the physician will not renew the prescription unless you are a much tighter leash. I doubt the physician's lab results are incorrect. These tests are standardized, relatively straightforward, and usually fairly accurate wherever they are taken.
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Avatar_f_tn
I have to clear up that my husband and I are not diabetic and have never been diagnosed as prediabetic.  Those high fasting tests were the first time for both of us.  That's why my question was whether the A1c which was normal is usually more accurate as far as a diabetes diagnosis than one fasting blood test.
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Avatar_f_tn
Just a follow up to my original post if anyone happens to be reading it.  My husband and I just had follow up glucose tests at Walgreens Diabetes clinic.  My husband's fasting test was 101, which he realizes is pre-diabetic but is more consistent with previous readings and a far cry from our doctor's lab which was 140.  My test was not fasting; I had had a light lunch (protein bar) 2 hours prior and my reading was 99, again not even close to my doctor's lab which was 127 fasting.  As I mentioned in my previous post, we've gotten questionable readings from his lab before (eg, my husband's iron level, which was always good, suddenly was very low, then normal again on the next test....I doubt the low reading was accurate).  Needless to say, I'm quite relieved.  Thank you for responding.
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535822_tn?1389452880
I would like to thank you all for the information here , whilst I am reading up and using the internet to educate myself on pre diabetes I have found the input given, as on this thread very enlightening, I am having the A1c test done tomorrw and you have given me more idea what its all about,the numbers etc,  thats what is so great about the Forums on MH we learn form others experiences.
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Avatar_m_tn
I have been testing blood sugar every morning for 4 months and vary between 97 and 134.  i find the time of the fasting and how late I have eaten to be very significant.  I had an A1c 4 months ago that was at 6.6.  Changed diet and lost 10 pounds and got a 5.5 one month ago.  Fasting glucose has stayed int that varied range.   What is eaten before bedtime seems significant.  I have been snacking on peanuts.   This seems to increase the Fasting glucose level in the morning.
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Avatar_f_tn
Thank you for your response.  I haven't had a high fasting test since that one last year, but my last A1c (about 6months ago) was higher at 5.8.  I've recently started taking cinnamon supplements which I read can help some people regulate their glucose.  I'll see if it makes a difference with my next blood test.  Congratulations on getting your A1c down. It's good to know which foods cause your blood sugar to rise so you can avoid eating too much of those foods.
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