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Q: A1C ( Answered 2 out of 5 stars,   0 Comments )
Subject: A1C
Category: Health > Conditions and Diseases
Asked by: alabama9-ga
List Price: $20.00
Posted: 14 Aug 2003 08:39 PDT
Expires: 13 Sep 2003 08:39 PDT
Question ID: 244715
I am looking for information on the accuracy of a diabetes test called
A1C. This measures "average" blood sugar over the last three months.
What is the accuracy on a lab test? On a Metrika test? Thank you!
Subject: Re: A1C
Answered By: alanna-ga on 14 Aug 2003 12:45 PDT
Rated:2 out of 5 stars
Hi alabama9-ga,

1.There are two ways to test blood glucose levels.  One is an "of the
moment" test which gives a picture of blood sugar on the day of the
test. This measures glucose freely ciculating in the blood.

The other is a test which gives an average blood sugar level over
time. This is the A1C test which measures glucose that is linked up
with red blood cells, usually over the past 2 or 3 months.

The A1C (glycated hemoglobin) test measures the percentage of red
blood cells that have glucose linked up to them. In  a non-diabetic
person, this is about 5%. That means about 5 in every 100 red blood
cells are glycated.  In a person with diabetes the percentage is
generally much higher, and can be as high as 25% when glucose levels
are out of control for a long period of time. The more glucose in the
system, the more it links up (glycates) red blood cells.

Once red blood cells are glycated, they remain so until they die off,
usually in about 6 months. As they die off, new red blood cells take
their place. If the new blood cells are not glycated due to better
glucose control, then the overall A1C percentage will decrease.

The American Diabetes Association recommends a minimum of two but
optimally three A1C tests per year.

American Diabetes Association "A1C test"

2. The accuracy of the A1C test depends upon the accuracy of the
testing methods.  The American Diabetes Association recommends that
all A1C laboratories use testing certified by the National
Glycohemoglobin Standardization Program (NGSP).  In the United States,
98 percent of laboratories do certified NGSP testing.

Additionally A1C laboratories may participate in proficiency testing
conducted by the College of American Pathologists (CAP). In 2003, all
participating A1C testing laboratories produced A1C measurements that
closely approximated the test samples provided by CAP. In other words,
their tests were accurate.

College of American Pathologists Survey Data 2003

3. The Metrika A1CNow is a single-use disposable A1C testing kit.  It
uses NGSP certified methodologies. It participated in the 2003 CAP
survey, and its results were comparable to other laboratories'
results. However, fewer test results were submitted compared to the
labs, therefore repeatability precision (how one test result differed
from the next) could not be measured at the time of the survey.

NOTE:  To read a site with the suffix .pdf, you need an Adobe Acrobat
Reader which is free from

search terms: AC1, "American Diabetes Association," "coefficient of
variance," "blood sugar" "circulating glucose"

I enjoyed finding out about the A1C test.  I hope my results were
useful to you.

All the best, 

Request for Answer Clarification by alabama9-ga on 14 Aug 2003 17:46 PDT
Thanks for all the info about A1C - I was familiar with that and my
question specifically rates to accuracy.  That said, you have given me
a good answer anyway!  But can you tell me more about what the
accuracy is, ie can you quantify it?  Is it within 10% of the "true"
number?  20%? Is the A1C test as accurate as teh lab test? Is there
any other reference besides the Missouri reference? Thank you.

Request for Answer Clarification by alabama9-ga on 15 Aug 2003 16:41 PDT
Is there an answer to my clarification request?

Clarification of Answer by alanna-ga on 15 Aug 2003 18:44 PDT
Hi alabama9-ga

Sorry for the delay.  I was caught in the East Coast blackout, and the
electricity (and my computer) just came back on.

The accuracy that you request can be found in the pdf table at

For example if you go to the first lab listed, Bayer DCA 2000, you'll
see how their test compares to the standard sample.  The sample
contained a percentage A1C of 8.7 (first column).  That particular lab
reported 8.8% A1C, off from the sample (your "true" number) by just
.1% with a coefficient of variance of 2.9%, meaning that repeated
tests on the sample were not highly variable.

If you go down to Metrika on that table, you'll note that their method
on the 8.7% A1C sample gave a value of 8.9.  There were not enough
repeated tests to qualify for a precision (coefficient of variance)

These proficiency testing results point to the accuracy of the tests
by lab.  Perhaps you are asking: "If my A1C is 10%, can I be assured
that that percentage accurately reflects my true A1C level?"  The
answer is yes within the limits of the laboratory you are using.
Results are considered accurate if the testing is certified by the
NGSP and the labs submit to proficiency testing.

In the Bayer lab test mentioned above, you could say that if your own
%A1c were 8.7 (the standard in the table) the lab might report it as

Hope this clarifies,

Clarification of Answer by alanna-ga on 17 Aug 2003 22:25 PDT
Hi alabama9,

I'm sorry that you're still not completely satisfied with the answers.
I'd really like to do that, so here goes!

I take it that by the "lab test" you mean the blood test that glucose
after a meal or after fasting or after glucose loading.  These tests
reflect blood glucose at the time of the test.

On the other hand, as you know, the A1C test gives a picture over a
period of time, so the two numbers are really not comparable.  They
are complementary.

But each test is accurate.  I have not seen the accuracy quantified in
my searches, other than the results I gave you previously.  However,
the prevailing method of measuring A1C, high-performance liquid
chromatography, seems to be the standard. As far as I can determine
from my searches, it appears to give the "true" or at least the
"truest" measure of "average" glycated hemoglobin levels.

For further discussion, see: 

The University of Missouri is the home of the Diabetes Diagnostic
Laboratory and the National Glycated Hemoglobin Standardization
Program (NGSP). "The purpose of the NGSP is to standardize glycated
hemoglobin test results so that clinical laboratory results are
comparable to those reported in the Diabetes Control and Complications
Trial..." carried out by the U.S. National Institute of Diabetes &
Digestive & Kidney Diseases over a 10-year period.  and 

The NGSP at the University of Missouri is the only body that certifies
laboratories that test for A1c.

I do hope this further clarifies your question.  


Request for Answer Clarification by alabama9-ga on 18 Aug 2003 21:37 PDT
Great answer. I want to change this rating to five stars but I don't
know how.  Thank you!! I hope you are okay and have the lights on
again ~

Clarification of Answer by alanna-ga on 19 Aug 2003 08:22 PDT
Thanks, alabama9-ga, I'm glad your pleased with the answer. 
Unfortunately, the rating can't be changed.

(From Google Answers FAQ):
"How do I rate an answer?
First, log in to your Google Answers account. On the "My Questions"
page, you'll see a list of all the questions you've asked so far.
Click on the question whose answer you want to rate. Rate the answer
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How do I rate an answer?"

That said, you might try an email:

Thanks again,
alabama9-ga rated this answer:2 out of 5 stars
I am still waiting for a clarification.

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