Falsely low or high HbA1c due to RBC lifespan

[finsit]

Even though A1c is largely used now a days for diabetes diagnosis, its still just a relative figure due to variation in our RBC lifespan.

There are some many conditions that can mess up with your RBC lifespan and your a1c could be lower or higher than the actual value.

A study showed that a lot of patients with G6PD deficiency and anaemia are misdiagnosed for diabetes because of falsely low a1c.

You may also have perfectly fine blood glucose but because your RBCs live longer, you may get a falsely higher a1c.

I have spent days researching how to correlate Red Blood Cell (RBC) lifespan with HbA1c and here are my findings.

Normal RBC lifespan is 100-120 days.

If your RBC lifespan is lower than average, your a1c is going to be falsely low. I still can't figure out in what proportion though.

If your RBC lifespan is higher than average your a1c is going to be falsely high.

I still can't figure out in what proportion though but trying to dig into papers to understand.

To calculate your RBC lifespan you will need to do some lab tests which is not easy to do so I found a way where you can estimate your average RBC lifespan

However the author put figures in units that we do not use in UK. So i had to further dig into how to convert these units.

So here is the formula and how it works.

What you will need: Reticulocyte counts and your CBC (RBC and Haematocrit). Retic count is normally not a part of NHS CBC test, so you will need to ask your GP and its fairly easy.

The retic number that comes back is in absolute count but for this formula we need it in percentage.

So to calculate percent retic count use the formula

Calculating Reticulocyte % age Number = Absolute retic count/RBC count

For example my retic count came back at 57. and my RBC count was 44.8.

My retic %age = 57/44.8 = 1.27%

Next thing you need to calculate is reti survival rate (maturation correction) using the table below:

So use the table to get your corrected maturation number. For example my haematocrit are at 42% so my retic survival correction number is (1) . Please note that haematocrit in UK are given in absolute number so just multiply it with 100. My haematocrit was given as 0.42 which makes it 42% if i multiply it with 100 (SURPRISE)

Now use this formula to calculate your RBC lifespan

RBC lifespan = 100/(retic%/corrected retic survival rate)

In my example it would be = 100/(1.27/1)

That is 78 days. My a1c always comes lower than my personal readings. My a1c comes back at 27 but in reality it should be close to 33.

I suppose if my RBC lifespan was 100 days, it would have corrected my a1c.

I already know that my RBC span is less due too G6PD deficiency, but didn't know the average. So now i know my RBC average but yet need to calculate

correlation between RBC lifespan and a1c.

Probably someone could help here? Please use below references to understand it further.


This is an interesting article and can be used to correlate RBC lifespan with a1c based on their observations on half life of these erythrocytes.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5094338/


This is where i got this formula

https://forum.fudiabetes.org/t/a1c-test-results-calculating-your-rbc-lifespan/3965

Thanks for reading and look forward to some more research by someone who can actually calculate a1c correction

 

[NicoleC1971]

I am aware of this issue with HBA1c but am not minded to calculate my Red Blood Cell turnover rate because unless is changes month to month then and with a firm diagnosis of diabetes, I will use the HBA1c to compare my blood glucose across time.
I would also be looking at my time in range and in the UK at least we have the means to do this.
If diagnosing someone it would be useful to look at fasting blood glucose and oral glucose tolerance ideally with corresponding insulin measurements.
Sorry I can't answer your interesting question but I fear it is diving into the weeds a bit since blood glucose is not the most important thing about type 2 at least!

 

[finsit]

I am aware of this issue with HBA1c but am not minded to calculate my Red Blood Cell turnover rate because unless is changes month to month then and with a firm diagnosis of diabetes, I will use the HBA1c to compare my blood glucose across time.
I would also be looking at my time in range and in the UK at least we have the means to do this.
If diagnosing someone it would be useful to look at fasting blood glucose and oral glucose tolerance ideally with corresponding insulin measurements.
Sorry I can't answer your interesting question but I fear it is diving into the weeds a bit since blood glucose is not the most important thing about type 2 at least!

Thank you for your reply. I just want to know how much i am off the calculated HbA1c, that's all.

 

[Bluetit1802]

I am also aware of this and have read up about it in the past as I believe my RBC are long lived as none of my HbA1c results have matched any other way of measuring that I have used over the last 6 or 7 years. All I look at now as regards the HbA1c are the trends rather than the absolute numbers.

Also, there are a few different types of machinery used in the UK to measure the HbA1c, and not all come up with the same results. It is pot luck which machine is the one used by the lab that our GP surgery uses. The lab used by my surgery uses a High Performance Liquid Chromatography machine. Another type is Affinity Chromatography used in a hospital in Salford. I don't know the names of the others.

After discussing this with my GP she arranged for me to give a blood sample, which was sent to both labs on the same day, the normal lab and the Salford lab. Same blood sample, two different results. One came back at 40, the other at 46 (from memory). The Salford one was the lower.

It really begs the question why the NHS relies so much on the HbA1c in the diagnosis of Type 2. There must be many, many people misdiagnosed. All we can do is keep an eye on trends.

 

[MrsA2]

It really begs the question why the NHS relies so much on the HbA1c in the diagnosis of Type 2.

What should they use instead?

 

[Riva_Roxaban]

I have recently had two units of blood transfused because my blood counts were down. Since having them my fasting levels have come down in to the middle five range from the sixes.

I do not know if this is just a coincidence, or the change in some of my medication where I have stopped taking anti inflammatories, anti coagulants. because of the internal bleeding in my colon.

I have been going to the pathology lab for years for my hba1c, and when I had the ogtt test done there which peggesd me as T2.

 

[HSSS]

A study showed that a lot of patients with G6PD deficiency and anaemia are misdiagnosed for diabetes because of falsely low a1c.

Don’t you mean a falsely high hb1ac causing a misdiagnosis when anemic “An earlier study showed that reduced iron stores have a link with increased glycation of hemoglobin A1C (HbA1c), leading to false-high values of HbA1c in non-diabetic individuals [2].” And “In iron deficiency, red cell production decreases, consequently an increased average age of circulating red cells ultimately leads to elevated HbA1 levels [16]”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3933917/

 

[Bluetit1802]

What should they use instead?

For diagnosis purposes only, an OGTT would be more accurate, then HbA1cs for reviews. I believe pregnant women are given the OGTT for diagnosis rather than an HbA1c because they may not have been pregnant and prone to gestational diabetes for the 3 months prior to the test and an HbA1c is unlikely to be accurate. That is just my thinking.

 

[HSSS]

For diagnosis purposes only, an OGTT would be more accurate, then HbA1cs for reviews. I believe pregnant women are given the OGTT for diagnosis rather than an HbA1c because they may not have been pregnant and prone to gestational diabetes for the 3 months prior to the test and an HbA1c is unlikely to be accurate. That is just my thinking.

But these are a lot more time consuming to do, so I guess more expensive, and the reason they are not used anymore.

 

[Bluetit1802]

But these are a lot more time consuming to do, so I guess more expensive, and the reason they are not used anymore.

Exactly!

 

[finsit]

Don’t you mean a falsely high hb1ac causing a misdiagnosis when anemic “An earlier study showed that reduced iron stores have a link with increased glycation of hemoglobin A1C (HbA1c), leading to false-high values of HbA1c in non-diabetic individuals [2].” And “In iron deficiency, red cell production decreases, consequently an increased average age of circulating red cells ultimately leads to elevated HbA1 levels [16]”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3933917/

@HSSS thanks for pointing that out. Yes iron deficiency anaemia would raise the a1c, you are correct. What i meant was G6PD and "haemolytic anaemia" that reduces the a1c. Here's the reference:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3912281/