Impact of giving blood on HbA1c, etc?

(David McCall) #1

Hi!

I’ve had this question rolling around my head for some time, and finally decided to come on here and ask it:
Does donating blood impact the results of an HbA1c blood test?

My understanding of how the HbA1c blood test is a reliable long-term (3months, I believe) marker for blood glucose, is that the blood cells that carry the glucose live for only 3months.

But if you donate blood shortly after changing to a ketogenic diet, presumably, the body would creat new red blood cells that have less glucose in them, and would therefore skew the HbA1c results?

I suppose another question would be what impact donating blood would have on other aspects of keto/fat burning adaptation?

Just curious!

(Bacon is a many-splendoured thing) #2

Forgive me for making a small correction: red blood corpuscles don’t carry glucose. Glucose is water-soluble, so it just rides in the bloodstream. What happens is that the glucose molecules bind to the haemoglobin in the red corpuscles, making them “sticky.” An HbA1C score measures the degree of glycation of the corpuscles. Since there is always minimum of about a tablespoon (teaspoon?) of glucose in your bloodstream at any given time, your red corpuscles are never going to be totally free of glycation (i.e., an HbA1C of 0.0 is impossible), but the lower your score, the better.

You are absolutely right that the reason the HbA1C score is used as a sort of three-month “average” of your serum glucose is that the red corpuscles live for a maximum of three months.

I would guess that you are also right that giving away a bunch of glycated red corpuscles would at least temporarily lower your HbA1C, until the new-made corpuscles had a chance to become glycated themselves.

I suspect that giving blood doesn’t really affect our bloodwork. Most of those numbers are pretty dynamic: for example, serum glucose and serum insulin depend on how recently our last meal was and what we ate, and cholesterol varies almost as readily. As for beta-hydroxybutyrate, I have no idea.

(Steve) #3

Right, but it pretty much HAS to skew the results, as you’re giving away about 20% of your blood volume and the HbA1C is a 3 month average, so that’s a pretty big delta.
What should also skew it would be the ketogenic diet that we’re all on. Keeping our carbs low and using fat as the primary energy source is also going to skew our HbA1C.
So, really, if you want an accurate test result, you’d have to stop donating blood and eat the high-carb food pyramid for three months. :slight_smile:

I guess the more important thing though, would be that, once you’ve been doing keto for at least 3 months and (at least for men) you can donate every two months, that the HbA1C number would be your new norm…and the way that your levels are trending, based on your new WOE.

(Doug) #4

~10% Steve, @fischersd one pint, eh? :slightly_smiling_face:

I think it takes 4 to 6 weeks for us to replace our red blood cells after donating blood, thus the 8 week waiting period in-between donations.

This is something of a head-scratcher for me.

It takes a while - that 4 to 6 week period - to make all the new cells, though. So it’s not like you get 10% non-glycated cells right away. I imagine the rate of new-cell creation is highest right after donating blood, and if so then it would make sense for some diluting effect to take place then - with blood glucose assumed to be the same, on average, after donating and before, then a relatively fast production of new cells should lower the percentage of glycated cells a little.

I also picture a sort of equlibrium where the more glucose and non-glycated cells that are present, the faster the rate of glycation. Right after you give blood, you’ll have less blood cells in you, but the percentage of glycated ones should stay the same, no?

(Probably more complex than necessary here, but there are different ways to test for HbA1c, and I’m not sure this is true for all of them. As long as the test compares HbA1c content to the total hemoglobin in the blood sample, then all should be well. I imagine the tests have to do that, since hemoglobin content varies enough among people that just counting the raw amount of it that’s glycated would introduce significant possible error.)

After donating, we’re going to add back in the lost 10% of cells over the new few weeks. During that time, our blood glucose levels will be working on the hemoglobin, so I don’t see how there could be too much of a swing.

(Bacon is a many-splendoured thing) #5

Doug, what I mean is that since the numbers are so volatile to begin with, giving blood isn’t going to really alter what we derive from testing those numbers. Yes, if you have a continuous glucose monitor, I imagine that the readings from just before the blood loss to right after will be quite different, but your glucose reading is going to change as soon as you eat something, anyway. So I don’t really see how the effect would be all that significant, especially for people who are only doing a fasting glucose draw every three or six months, anyway.

(Doug) #6

Paul, I don’t think A1C will be volatile, though. It certainly should not be.

Glucose - most definitely volatile in comparison, as long as we’re eating. Even the "Dawn Effect’ or other daily cyclic things might alter glucose levels while fasting enough that the percentage change would be problematic if A1C readings were affected the same way.

(Steve) #7

Heh…my bad…I thought we only had 5. :slight_smile:

How much it’s going to skew the HbA1C really depends on when you get the test done, relative to when you donated. If you get tested right after, then it should be a fairly accurate number…but once that 10% gets rebuilt, the new blood will only have about a months worth of glucose attached to it.

But, again, if donating is a regular thing and keeping keto is the new norm, then the HbA1C will still show trending…which is really what’s important.

(Doug) #8

:sunglasses: Exactly right, Steve. So there should be some dilution effect and lower A1C readings.

Only thing I question is the “equilibrium” thing, i.e. there’s always hemoglobin and glucose in our blood, so the rate of glycation must be slow, like there’s only a miniscule chance that a given cell will hook up with some glucose on a given day. A higher percentage of non-glycated cells should increase that rate, assuming the same amount of glucose, but I don’t know how much. Surely not enough to much alter what you said - the new blood won’t be nearly as old as what the average was before donating.

#9

Not exactly on topic but I’ve heard a few times that donating blood can be beneficial in terms of getting rid of heavy metals. I guess that’s assuming you have heavy metals you need and/or want to give away.

(David McCall) #10

Thanks for all of your replies!

I wasn’t aware of the distinction between blood glucose and glycation; will have to look into that more deeply!

My thinking was that the hypothetical A1c would be taken after the body had had sufficient time to replace the blood that had been drawn. I was assuming that the newly created red blood cells would not be generated with the same level of glycation as of those in the donated blood. And that there would be a dilution effect on the remaining remaining highly glycated corpuscles.

Wondering now, what is the impact of ‘sticky’ hemaglobin is on arterial and veinous walls? I mean, if cholesterol particle size is potentially damaging, wouldn’t an excessively ‘sticky’ substacne in the bloodstream be bad as well?

At any rate, thoroughly interesting reading through all of your replies! Thanks again!

(CharleyD) #11

If platelets get sticky, they can cause a clot. Glycated Hemoglobin on red blood cells is just a usually reliable enough indicator, since they have to have glucose for their metabolism.

(Frances Brunner) #12

A related question…how would donating platelets affect A1C? In the past I was a somewhat regular platelet donor. I am wondering because it is a reduction in blood volume. A benefit, a disadvantage, or neutral? What say you?

(Bacon is a many-splendoured thing) #13

Platelets don’t contain hemoglobin, do they?