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hba1c does not match glucometer

L

Luca2016

Well-Known Member
Messages
61
Type of diabetes
Prediabetes
A couple of days ago I had an hba1c and fasting bsl done at the lab.
My hba1c came back at 30 or 4.9 and fasting blood sugar level came back 5.0.
I checked my fasting level before I went into the lab and according to my meter it was 6.0 which it is pretty regularly.
from my meter readings I expected my hba1c to be around 36 or about 5.5.
I have iron deficiency which may help explain hba1c but fasting level? I don't get how that could be so different to my meter.
It would be easy to assume my meter was reading higher than it should be but today my fasting level was 3.8 so I don't think it could have been lower than that.
Does anyone have any idea about what might be going on?
I had an albumin test done too which was normal which suggests that I dont have kidney or liver disease which can skew hba1c results.
 
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Mine doesnt match either. My FBG according to my meter which I did as the lab drew the blood was a full point lower than the lab. So when I was seeing a 4.9 on my meter it was actually 5.9. My A1c is higher than I expected. Meters can be out by up to 20%
 
Thanks for your reply. It's so annoying though eh. I regularly get fasting levels of around 6.0 these days which I really don't like but now I'm like are they accurate or what?
 
The numbers you obtain from a meter will generally be different to those obtained in the lab, and also to those obtained from other meters. The higher your number is, the higher the degree of inaccuracy.
 
What you mean to say is your *glucometer does not match your HbA1c.

Meters can give estimates and that's great because it can give you a rough idea of how your doing over all. Rough being the operative word here.

Glucose meters will only give you an A1c estimation with respect to the measurements you've taken. The lab test (to put it simply) works out the differences in glucose content of blood that is stuck to the A1c proteins in your body. This is how they can calculate an average value over the course of 2-3 months, because that's how long these proteins are around.

I'd say that's more accurate than your meter.

Grant
 
The meter reading is to tell you your numbers are high, low and have changed to higher or lower than your last reading.
One day I tested my sugar to be 7.2 then off to a&e they read 9.7, on a different meter and I was stressed and missed a meal and injection by time I was seen.
I was proud of my low bgs but my meter and their's showed otherwise.
No check for acidosis which the meter doesnt recognise on dapagliflozin or canagliflozin either.
 
Your average readings on your meter are not reliable enough to estimate an HbA1c unless you do finger prick tests every half an hour 24/7. You have no idea what is going on in between your tests.

As you say you have iron deficiency anaemia and other conditions these will no doubt have skewed your HbA1c. It is well known and proved that anaemic issues give false HbA1c results.

It is also important to remember that lab tests are done from venous blood and it is the plasma that is checked. Finger prick tests are capillary blood and it is whole blood, not plasma. Whole blood contains more glucose than plasma blood. Unless your particular meter has an inbuilt calibration to convert the whole blood reading to a plasma reading, there will, on average, be a 12% difference. The meter will read higher than the lab test by around 12%. If your meter is a Codefree or an Accu Chek Mobile, these meters are calibrated so no need to deduct/add 12%. I have no idea if others are.
 
 
Sorry I am confused. do whole blood samples from meters more accurately reflect how much glucose is in your blood because it measures your whole blood instead of just part of your blood as measured by the plasma samples in the lab? so if you had a meter that measured plasma blood glucose would that not tell you how much glucose is really in your blood because it would be lower than whole blood measures?
 
I wouldn't be concerned or get tied up in the differences between plasma blood glucose and whole blood glucose.

The important thing is to have a good HbA1c that is as low as you can. All meters have to conform to testing standards to ensure they are accurate enough before being sold.

The HbA1c lab test result is all you you need to focus on. This is as accurate as you can get. Enough said.

You can read this recent thread from @tim2000s which highlights the differences and may clear up your confusion between plasma and whole blood:

http://www.diabetes.co.uk/forum/threads/whole-blood-glucose-vs-plasma-glucose.104816/

Don't worry about meter accuracy, just keep the numbers down!

Grant
 
The original poster's question is intriguing. But it didn't say when was the most recent home fingerstick before the lab fasting glucose measurement.

To ensure accurate measurement, first rinse the skin well. Just by touching a banana skin, for example, you could pick up enough sugar to spoil the measurement.

Many if not most glucometers in America are calibrated to plasma. In Britain, all but 2 glucometers are calibrated to whole blood (said a post in these forums this month).

The "true" clinical measurement of glucose levels is calibrated to plasma -- the lab test of fasting glucose, is a fasting plasma glucose test, FPG. The conversion between whole blood calibration and plasma calibration depends on the value of the 'hematocrit (haematocrit)' (the proportion of red cells in the blood), which is one of the measures of the blood's content of red cells and haemoglobin. I suppose a person with iron deficiency anaemia also has an abnormal haematocrit, and this could throw off the glucometer reading.

The A1c is systematically inaccurate when there are interferences. Some interferences cause a false high, others a false low. Iron deficiency anaemia will cause a falsely high A1c (cause an elevation). This was reported at least as early as 2007. A 2014 Iranian study confirmed it (and found also that the effect is even greater at fasting glucose levels in the American defined prediabetic range of 5.5 - 6.9). A 2015 article reports a rare population based study: Implications of iron deficiency/anemia on the classification of diabetes using HbA1c. Nutrition & diabetes 5. One of the findings was that "Fewer participants with ID alone versus normal iron/hemoglobin were classified with diabetes using HbA1c only." This reflects that I.D. elevates the A1c result.

The whole blood figure is lower than the plasma because the glucose is in solution in the plasma, and the removal of the blood cells reduces the sample volume, thereby concentrating whatever is left.
 
sud5nala said:
Many if not most glucometers in America are calibrated to plasma. In Britain, all but 2 glucometers are calibrated to whole blood (said a post in these forums this month).
Click to expand...

There are definitely two glucose meters calibrated to plasma in the UK. (Codefree and Accu Chek Mobile). What I think was said on another thread is that the poster didn't know about other meters. It was suggested that people look in their meter leaflets in the technical specifications to see if they are, or on the maker's website.
 
thanks for your comment. I tested on my meter five minutes before blood draw at lab and after, both readings were 6.0. my meter apparently measures whole blood.
I have read studies which have opposing views regarding the impact that Id has on hba1c with some suggesting it lowers it and some suggesting it makes it higher. I had my haemoglobin measured too and that came back normal but my mcv came back just above the threshold for normal.
I'm still confused
 
Bluetit1802 said:
As you say you have iron deficiency anaemia and other conditions these will no doubt have skewed your HbA1c. It is well known and proved that anaemic issues give false HbA1c results..
Click to expand...

that's interesting.... thanks. No one here has ever told me that. Does it work the same way if you have too much iron in your blood? I get iron infusions as I have iron malabsorption. I had an iron infusion at the end of last year and they took my level from 17 to 368 when the maximum is 300. The minimum level is 30 and because I lose iron and don't absorb it they fill me right up with it. I have no idea what I am right now as I only get a test every 6 months or so. But if my iron level is high my guess by what you're saying is it may affect my hbA1c too? I just had that done and find out the result next week. Another question to ask my endo when I see him in a few months. Mind you I'm not expecting a good hbA1c this time as I've been quite sick the last few months and my sugars like going higher during those times.
 

Confusing, indeed. Plasma glucose is something like 12% higher than whole blood. Your FPG from the lab was 5.0. The lab numbers have more weight, fortunately!

Capillary glucose measurements (eg, fingersticks) are usually higher than lab FPG. I have read more than once that the difference is about 10%, and I read one such study while composing my previous post.
 
Totally annoyed now.. Does that mean I might not be T2 after all? (Im anemic)
I have regular blood tests (ongoing condition) & not once was diabetes mentioned. Had a test Tuesday, results Thursday.
1st thing he said was I really low in iron. Prescribed Folic acid. Then he said I was diabetic, prescribed metformin & basically sent away.. (not taking the metformin) I was 8.0.. With cutting carbs & hitting the veggie's (more iron) my meter tests have gone down. 5 on waking today, 5.4 before lunch & 5-2 two hours after.. & thats in 6 days..Will be interesting to see what the morning readings is.

Update. 4,7 on waking
 
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I have three meters (just coz I'm a bit sad), they each give me a meter reading that collectively are out by a range of 2.0mmol, so there is definitely a variance at this level of equipment/ specific batches of strips

I would happily rely on your A1C




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