November 16, 2012
Is Your A1c Just Another Number?
Do you consider your A1c just another number? I admit I do not understand people that treat it this way and ignore what it is telling them and their doctor. One of the people in our informal group looks at the A1c just this way. Granted, his current A1c was a great improvement over his last A1c of 7.3%. He is unexcited with this one and says it is just one more reading. Yes, 6.6% is still above the AACE (American Association of Clinical Endocrinologists) recommendation of 6.5%; and he is still in an area where his complications can continue to develop.
When the three of us that were with him asked what number would excite him, his answer was none. He said he does not pay attention to the A1c's and only watches his daily blood glucose readings. He says those are important to him and is worth the extra cost of test strips as he tests as high as nine times a day.
Why do I care? Because I see articles on this almost on a quarterly basis and like this one, they are too short and often have missing information. Can the A1c be used initially to screen for diabetes? Some doctors do use it for screening. Other doctors prefer a fasting blood glucose (FBG), the oral glucose tolerance test (OGTT), and the A1c before they will diagnose diabetes. Another test in the diagnosis arsenal is the fasting plasma glucose (FPG) test. Still other doctors will use other tests to make sure it is type 2 and not type 1 or LADA. The C-peptide is also used to determine insulin resistance or the amount of insulin your body is producing. Levels of autoantibodies to insulin and the beta cells can be of some value but even these do not lead to an airtight diagnosis. This is because not all people with type 1 have these antibodies. Therefore, the diagnosis is still largely a clinical one.
There are others writing about A1c tests. David Mendosa has an explanation I have not seen before and you can read it here. I was aware that there is a variation in how long our red blood cells do live and that this can affect our A1c readings. David's blog covers much information that needs to be learned and retained by everyone. Tom Ross blogs about the A1c almost monthly lately by listing some of the search questions bringing people to his site. They are also very informative and he often adds some humor. The October blog is here and the September blog is here. Next we can read Gretchen Becker's blog here about the A1c as she discusses accuracy.
The source that I use and depend on is the lab tests online dot org website. The reason I like it for my reference is that it covers topics most blogs and articles about the A1c do not even mention. Did you know that the A1c is not reliable for the following?
1. diagnosis in pregnant women,
2. people who have had recent severe bleeding or blood transfusions,
3. those with chronic kidney, liver disease, or are on dialysis.
4. people with blood disorders such as iron-deficiency anemia, vitamin B12 anemia, and hemoglobin variants.
“Only A1c tests that have been referenced to an accepted laboratory method (standardized) should be used for diagnostic or screening purposes.” Too many doctors tend to ignore this statement and diagnose anyway. This begs the question of what doctors are thinking when an A1c test results in excess of 7.0% and you are only given this statement, “Be care what you eat as your blood sugar is a little high.” Oh really – do they think they are being kind when they don't schedule you for more tests or have you return another day for the other tests to check if you are a person with diabetes. Any A1c over 7.0% should require more testing to determine if you have diabetes.
Other facts you may be wise to know:
1. The A1c test will not reflect temporary, acute blood glucose increases or decreases. The glucose swings of someone who has "brittle" diabetes will not be reflected in the A1c.
2. If you have a hemoglobin variant, such as sickle cell hemoglobin (hemoglobin S), you will have a decreased amount of hemoglobin A. This may limit the usefulness of the A1c test in diagnosing and/or monitoring your diabetes.
3. If you have anemia, hemolysis, or heavy bleeding, your test results may be falsely low.
4. If you are iron deficient, you may have an increased A1c measurement.
5. If you have had a recent transfusion, then your A1c will be falsely increased (blood preservative solutions contain high glucose levels) and not accurately reflect your glucose control for 2 to 3 months.
The following formula ADAG (A1c-Derived Average Glucose) is used to calculate your estimated Average Glucose (eAG) from your A1c result.
28.7 X A1c – 46.7 = eAG
An example of this is an A1c of 6%. The calculation for this would be:
28.7 X 6 – 46.7 = 126 mg/dl
for an estimated average glucose of 126 mg/dl. I repeat this is an estimated average because your blood glucose readings from your meter will generally not be close to this average. The variance is due to the timing of your meter readings and will not reflect an average.
What this means is that for every one percent that your A1c goes up, it is equivalent to your average glucose going up by about 29 mg/dl. For a printable chart conversion table for eAG click on this link.