can you have a negative false test

I was wondering a few thins. My paternal gramother was in her late 60's early 70's when she was told she had diabetes. My dad was diagnosed in his late 50's with it. I am 37. I can't say that I am thirsty all of the time, but I have to urinate all of the time. I have had a full test to see if my bladder was okay  and had test for other things. I have Neurofibromatosis type 1. From what I understand NF can mimic many diseases, like diabetes and thyroid. I am too tired to function many days and my bp is usually low 90/54 -95/63. both thyroid and diabetes run in the family (lucky us) anyway, my 3 questions are should I be tested for diabetes, even though I have no real symptoms, can a genetic test be done to see if I can am at risk of getting it? Finally, can you have blood work done, fasting of course, and have it come back being a false negative
Thank you so much for all of your input
Michelle

[Anita Ramsetty, MD]

Hi,
I do think you should be screened for diabetes given your symptoms and family history, as well as your having NF1. There is no specific genetic test for type 2 diabetes at this time, but for consideration of Type 1 diabetes(which I do not think you are very high risk of getting) antibodies to GAD and Islet cells can be checked. The accepted ways of screening for diabetes are a fasting glucose, a random glucose(not as good) or a 2 hour glucose tolerance test. A HgB A1C is sometimes used by doctors but it is not widely accepted as a good screening measure, so I suggest a fasting or an OGTT.
You should also have a thyroid screen(TSH) done.
Fasting glucose is not perfect, so yes you can have a "false negative" in terms of saying you have no abnormalities in glucose handling. A small percentage of folks will test positive and negative just a day apart using this test--this is the problem with using one number as a cut-off. If you are concerned, a 2 hour glucose test(also not perfect) can also be used to determine not only fasting but also glucose challenge results.
Hope this helps.
take care.

[KevinHarney]

Yes there are two tests that can be done to test for diabetes.

First is A1c.  This tests % of sugar in your blood over an extended period of time being approximately 3 months.  It is a simple blood test and can be done by any Dr.  and I believe that you can buy a home test kit at any pharmacy to do it yourself.  Though I think if you go this route you have to sent the sample to a lab and wait for results - same as the Dr. only cheaper.

Second test is a GTT (Glucose Tolerance Test).  This is a longer test that measures your blood sugar levels  before during and after consuming specific levels of Glucose over a specific period of time.

I have not heard of any false positive readings on either test but I do not know that for sure.

[tigger08]

can you get a false reading(saying your taking a drug that your not) after you have passed out. my sister did this and was sent to the hospital and they are saying she overdosed on a pill that she isnt even taking. she had some bleeding in her brain too.