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How to calculate your RBC lifespan using CBC

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.

This is where i got this formula

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

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