What does the A1c mean?

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zrebiec Posted: Thu, Dec 18 2008 10:46 AM

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Topic: A1c... (1 of 3), Read 59 times
Conf: Newly Diagnosed
From: ds9127 ds9127@gmail.com
Date: Wednesday, November 12, 2008 10:05 AM

I started out as 9% then went to 7% now 6.3%. First, what is this number? Second, what does it have to do with a 30 day average? Third, where should this number end up?

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Simi_Papa replied on Thu, Dec 18 2008 3:54 PM

It is a measure of your average bg level over the last 3 months, at least that is the theory.  Normals have a reading less than 5.5 and your goal should be below 6.  The better your control, the less likely you are to develop diabetic complications (again, that is the theory).  What medications are you taking?  How are your lipids (cholesterol)?  Those numbers are also very important to diabetics.

Bill

"May the Force be with you!"

Diagnosed in 1997; Off all meds except Metformin!! Smile

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zrebiec replied on Tue, Dec 23 2008 3:19 PM

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The A1C is a measure of how much your red blood cells have been exposed to glucose. An average A1C for a non diabetic is generally considered to be less than 6, although I would say it is probably 5 or less. The higher your average blood sugar is, the more hemoglobin gets glycated (attached to a glucose molecule) and eventually takes a specific shape which is noted as A1C. Red blood cells live approximately 120 days, so the average glycated amount is reported as your A1C and is therefore a measure of your average blood sugar levels for the last 60 to 90 days time frame. Of course this assumes you have no other blood related pathologies that would skew the results.
Metformin, Actos, Zocor, Synthroid, and Exercise

Madman

Here is some information on A1C and how it relates to average BG. I strive to get under 6.0% but as of late I have been getting 6.1-6.2%.

http://www.diabetesincontrol.com/issue99/PatientResultForm.pdf

Ron

Caveat Emptor - Not a medical professional, just another diabetic. Type 2 taking Prandin (1,1,1), 14U Levemir (bedtime), ramipril 10, indapamide 1.25, Crestor 20, & Aspirin. Diagnosed Feb/01.

"I have not failed. I have just found 10,000 ways that don't work." - Thomas Edison

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I hope someone here might be able to give me more details about how the A1c value is actually calculated. I will explain in the next paragraph why I am looking for this information. It appears that a A1c value of 6.0 is showing that your average blood glucose reading was approximately 120. This means you had sample readings (A) such as these: 50, 60, 100, 110, 130, 120, 180, and 190. Or you could have an A1c of 6.0 with sample readings (B) of 90, 100, 110, 115, 125, 130, 140, and 150. As you can see the same A1c of 6.0 can be produced with different blood glucose levels but clearly see that the person with sample B had better control.

So I am looking to see how the A1c value is calculated? Is it taking multiple samples? Or one sample of blood with multiple glucose indicators? In either case, it would appear that a standard deviation (the variability of the samples) could be calculated (not to be confused with standard error.) So with sample A the standard deviation would be higher than sample B. The standard deviation would give people a better idea of how well their control is. For myself, I had 5 years of A1c readings of 7.0 yet sometime according to my records I had great control and other times really poor (or fluctuating) control.

If this is doable, how does someone do about convincing the medical labs and professionals that this is worth doing and would give Diabetics an even more accurate test?

Kristin

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kat replied on Sun, Apr 12 2009 8:49 AM

Hi, Kristin, and Welcome -

Until the more statistically and mathematically inclined reply to your post, here's a simple explanation AlC:

As I understand it, HbA1C is not actually an average value, it is a weighted value.  Higher blood glucose nearer to the time of the A1C test will be more significant than higher blood glucose at the beginning of the test period which is usually three months.  For a very simple explanation of A1C, check http://www.nlm.nih.gov/medlineplus/ency/article/003640.htm

Hope that helps.

 

T2, diagnosed 12/98.  Diet and exercise 2/03 - 11/08.  Now back on metformin 500 ER.

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Ron AKA replied on Sun, Apr 12 2009 9:20 AM

Love_Dark_Choc:
So I am looking to see how the A1c value is calculated? Is it taking multiple samples? Or one sample of blood with multiple glucose indicators?

Kristin, the A1C is measured from a single blood sample, so there is only one test result. There are no multiple numbers to calculate a standard deviation from. As I understand it at elevated blood glucose levels some glucose attaches to the surface of the red blood cells. Roughly it is the % of glucose on the red blood cells in the sample. Some believe that this attachment is permanent (for the life of the blood cell - 2-3 months), while others believe the glucose can come unattached to some degree when BG goes low. Further in some people with the same BG levels there will be more or less attachment. In any case if you have high BG, the glucose attached will be higher than average. The real question is what does it mean. While you will find charts and formulas to convert A1C to average BG, for the reasons just given, I don't believe this conversion is all that accurate when you look at one person, rather than an average of a bunch of people. And you point out another issue with the test in that it does not show the extreme variability of BG over time.

My opinion is that the test is overused by doctors to measure BG control. It is simple and they don't have to look at all your real BG numbers and try and figure out what they mean. However, they loose the detail. So my view is that keeping BG records and charting them is the best way to figure out what is happening. Some software programs will calculate standard deviation for the different time slots of the day for example. That is the real way to measure your BG control.

Hope that helps some,

Ron

Not a med prof. Just diabetic type 2 on Prandin, Levemir, ramipril, bisoprolol, & Crestor. Diag. Feb/01.

"I have not failed. I have just found 10,000 ways that don't work." - Thomas Edison

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zrebiec replied on Mon, Apr 13 2009 8:31 AM

What is it?

A laboratory blood test that tells what your average blood glucose has been over the past two to three months

 

This information on “long-term” control plus your day-to-day blood glucose levels helps you and your team to design and revise your diabetes management plan so that it works for you.

 

What does it measure?

 

 

The test measures the amount of glucose that attaches to hemoglobin, the part of the red blood cell that carries oxygen.  As the hemoglobin travels through the bloodstream, it picks up glucose (glucose) that is in the blood; the more glucose in your blood, the more glucose attaches to the hemoglobin.  

 

Since red blood cells have about a two to three month life-span in the body, we are able

to measure the “glucose coating” of a sample of hemoglobin.

 

Anemia or any condition that effects red blood cell life-span or concentration may alter the results.

 

Why is it important?

Keeping your blood glucose as close to normal as possible will decrease the risk for diabetes complications from developing or becoming worse.  The higher your hemoglobin A1c results are and the longer they stay high, the greater your chances of developing complications.

 

How often should it be done?

People with diabetes should have a glycosylated hemoglobin A1c, or “A1c”, at least 2-4 times a year.   Ask your health care provider how often you should have one done.

 

 What do the numbers mean? 

1.      To help you understand what your A1c number means, first, see where you are now.

2.      Then compare where you have been.  

3.      Use the guideline below to determine what the number means for the general population. 

4.     Know your A1c goal.  This should be decided on by you and your health care team. 

 

4.0 – 6.0%

Non-diabetic range

You are probably not having a lot of high blood glucose, but you may be having a lot of low blood glucose readings.  Contact your health care team if this is so.  This range is too low for most people who require insulin to treat diabetes. 

 

6.0 – 7.0%

If you are here and not having too many lows, your diabetes management plan is working well.  If you are having a lot of low blood glucose, changes in insulin or diabetes pills, food, and exercise may be necessary.   Ask your health care team what changes are needed.

 

>7.0%-10%

If you are here and consistently over 130mg/dl pre-meals or 160 mg/dl 2 hours after meals, you need to check blood glucose more often and change your diabetes treatment. Consider an appointment with your health care team to discuss if any changes in insulin or diabetes pills, food, and/or exercise should be made.

10.0% or greater

Your diabetes management plan needs to be reviewed NOW. Make an appointment with your health care team today.  Ask your health care team for help in making changes in insulin or diabetes pills, food, and/or exercise.

 

Remember, the A1c is an average of all your glucose levels. 

 

If you are having a lot of high and a lot of low blood glucose levels, you need help from your health care team even though your A1c is in a desired range!

 

 

 

                                                                       

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Madman replied on Mon, Apr 13 2009 1:07 PM

A1c is a good way to measure overall control, it is quick, efficient, and not too costly.  It does not, as Ron stated, tell the whole story.  It is simply an average and can be falsely leading.  It can mask very high postprandial readings due to lower fasting readings or even rebound hypoglycemic episodes.  In other words, one may be experiencing rather high glucose readings after eating, but going low sometime after that or overnight. Thus you are still experiencing high glucose periods that can still be damaging, but the A1c may not show this.

Both the A1c and a record of glucose readings is best to accurately manage this disease, in my opionion.

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Hi, Thank you all for your quick replies to my recent posting.

Just to be clear, I am not evaluating if BG or A1c is good or bad or is one better or more accurate than another. My point in writing was to find how the A1c value is calculated. I believe Ron got that point. But I would be interested in hear more.

I was under the impression that when a red blood cell is created (born) it has an marker that indicates the BG level at the time it was created. Do more indicators get added with time, thereby allowing the A1c test to look at only 1 blood cell? If more indicators do not get added, then the A1c value would have to be calcuated based on multiple blood cells. This is what I am hoping for, as then a Standard Deviation (see posting on Sat, Apr 11 2009 7:46 PM for more details) could be calculated.

Looking forward to more information. Kristin

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Spirit replied on Mon, Apr 13 2009 5:47 PM

During the life of an A1 or A1c hemoglobin cell (about 120 days) glucose from the bloodstream can attach to these red blood cells.  This glycation of red blood cells is an ongoing process.  When the HbA1c test is performed, the result is a number that is the percentage of molecules of glucose that are attached to the hemoglobin in the blood sample drawn.  So, an A1c result of 6.5 means 6.5% of the blood drawn shows glycation (sugar attached).  It is a single measure of a single sample expressed as a percentage. 

Since normal values for the HbA1c test are 4% to6%, I suppose you could consider 5% to be the mean and 1% to be the standard deviation (if you are looking at a standard deviation only to define a statistically significant variance).  So, above 6% takes you out of the normal range, above 7% is a statistically significant rise and so on.  In fact, that's pretty much what many of the guidelines show.  An A1c of 6.0 is great, one of 7.0 means a review of treatment is needed.

Our daily meters measure something different from the A1c.  They measure how much glucose is in our bloodstream at any given moment in time, expressed in milligrams per decilters. 

So, the daily test and the HbA1c can be strongly correlated, but the A1c is not just a statistically derived average of all of our daily readings.  They measure different things and are expressed in different values and are time related in different ways (A1c over a three month life of the cell versus daily readings that reflect only a momentary result, subject to change over a short period of time). 

I'm not sure this information will help in your quest about a standard deviation for the A1c.  Perhaps it would help if you could be clearer about why you are searching for the answer to your question.  What information would a standard deviation yield for you?

 

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Hi,

To clarify for Spirit and for others, please read my posting on Sat, Apr 11 2009 7:46 PM for more details about why I am looking for the standard deviation and not the 1% variance that Spirit mentioned. But anytime a number is calculated based on a percent (meaning you have taken more than one value to get an average) you can get a standard deviation. This is what I am looking for, just need someone who is familiar with the A1c formula to clarify if this is the case.

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Ron AKA replied on Mon, Apr 13 2009 7:40 PM

Love_Dark_Choc:

Hi,

To clarify for Spirit and for others, please read my posting on Sat, Apr 11 2009 7:46 PM for more details about why I am looking for the standard deviation and not the 1% variance that Spirit mentioned. But anytime a number is calculated based on a percent (meaning you have taken more than one value to get an average) you can get a standard deviation. This is what I am looking for, just need someone who is familiar with the A1c formula to clarify if this is the case.

Kristin, I don't think you are quite understanding what the A1C is. It is essentially the % of glucose on the hemoglobin in the single sample taken on a gross basis. I believe only one sample is taken, and the formula is just grams of glucose (G) divided by grams of hemoglobin (H) plus grams of glucose and then times 100 to get a percentage. So you only need two numbers to calculate A1C; weight of glucose and weight of hemoglobin.  The formula would be A1C = G/(G+H) X 100. When they say that the A1C is a real average, and is just an approximate assumption of what the average might have been. Since blood cells only live 2-3 months, they assume that the blood cells alive at the time of the sample represent the past 2-3 months, because older ones would be dead and filtered out of the blood (by the liver??). Probably because blood cells die on an exponential curve then there are likely more new cells than old cells, so the estimated average is bias towards the newer cells.

From the first post I understand what you are trying to determine, but the A1C is just not that sophisticated. On the other hand if you take 30 BG readings per month, then you can calculate an average and a standard deviation.

Ron

Not a med prof. Just diabetic type 2 on Prandin, Levemir, ramipril, bisoprolol, & Crestor. Diag. Feb/01.

"I have not failed. I have just found 10,000 ways that don't work." - Thomas Edison

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Spirit replied on Mon, Apr 13 2009 9:16 PM

Dark chocolate:  I have reread your initial post and I'm afraid I'm still not clear about what you are seeking.  The HbA1c is a single result based on a single sample, expressed as the percentage of glycated red blood cells found in that sample.   Percentages do not have to have a long series of numbers to be valid.  If I put one cup of bleach and nine cups of water together in a bucket, I have a 10% bleach solution.  No series of numbers to average.  Same idea with the A1c result. 

Perhaps the confusion comes in because HbA1c results are often "translated" into an average blood glucose level, presumably to make the results better understood by patients.  Since we test often and are intimately familiar with the milligram to decilter terminology we see on our meters, the A1c result perhaps becomes more meaningful if the vocabulary is changed from 7.1 percent  into  average blood glucose of 150

But the A1c test itself is not a computed average of our daily glucose readings from our meters. It is a different test altogether.  It is a simple percentage expressing how much of the A1 or A1c hemoglobin cells have become coated with glucose.   You can't compute a standard deviation on only one number.

As you showed in your original post, two different sets of recorded daily readings can yield the same A1c.  Our daily readings are only "snapshots" of what is happening.  We may be missing some lows and highs or only catching some lows or highs and missing lots of good numbers.  So, we need both the A1c and the daily readings in order to really get a handle on how we are managing our diabetes.  Using only one won't give us all the info we need. 

Using the A1c and our daily readings in tandem helps us in making informed decisions about diabetic treatment.  If an acceptable A1c matches acceptable daily readings, then all is well.  But if the A1c and our daily readings do not match (as you demonstrated in one of your examples), then there is a problem and we need to do something about it.  We may be missing highs or missing lows by not testing at correct times or frequently enough or we need an adjustment in diet, exercise or medication.  Both tests give us data to go by.  They can complement each other. 

Sometimes it might be the A1c result that points to a problem.  Sometimes it might be our daily meter readings that signal a difficulty.   Good thing we have both.

Is it this possibility that A1c results may not match our daily readings all the time that causes the problem for you? 

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Hi, To all,

I completely understand that the A1c test gives a single number, but what still has not been answered is how that number was calculated? There might be hidden in the details more information than just that number, but it is not calculated and not revealed to the patient.

From the comments of past posters, we can see that a single number does not give a complete picture. I am hoping that a lab researcher familiar with the process for calculating the A1c value, might be inspired to do further research to get a more accurate value (and maybe a test named after them!) or they could call it the Dc1 (dark chocolate 1) test. Wink

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Ron AKA replied on Mon, Apr 13 2009 11:56 PM

Dc1, I think you are trying to get "blood out of a stone". The A1C is like measuring the tread thickness on a tire before a race, the miles run, and the tread left after the race, and then estimating average speed. I'm sure the higher the average speed, the more tread will be lost on the tire. But there is no way from the tread wear that you can figure out how fast you were going on each lap of the race, or further still what the slowest lap was and the fastest.

I'm curious however why you are so concerned about the A1C number and that it may have some hidden value not revealed to the patient? If you were to share, we may be able to help some.

Ron

Not a med prof. Just diabetic type 2 on Prandin, Levemir, ramipril, bisoprolol, & Crestor. Diag. Feb/01.

"I have not failed. I have just found 10,000 ways that don't work." - Thomas Edison

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