Lab Savvy...HgA1c

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I'm not sure if this is a "med savvy" or more correctly "lab savvy" but it seems to fit here best - I guess I'll see if it gets moved...

My question is about HgA1c - not what it measures - I understand what I've been told that sugar in the bloodstream can become attached to the hemoglobin in red blood cells (glycosylation) - my question for the brainiacs out there is....how does the sugar GET attached to the hemaglobin? RBC's are cells with cell membranes and if you are diabetic and don't have the insulin there to play "gatekeeper" and let the glucose in, how the heck does it so freely get into the RBC's in the first place? What am I missing? :confused:

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Specializes in ICU, Psych.

As far as I can remember, RBC loose their nucleus early in development, and later on most of the other stuff inside them including their mitochondria, aka power-generator.

But RBCs do use glucose as a fuel source kind of like yeast does, by process of fermentation or something like that. I think in fact RBCs are closer to yeasts then to regular other human cells. It requires no insulin to do this, and so it gives a true picture of the blood glucose levels, what finger-sticks do not since insulin can and does influence them. So it does take up glucose, and thus the A1C give you a picture of the amount of average glucose that RBCs are exposed to during the 120 days that they are alive.

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Specializes in ICU, Psych.

P.S.

I think the main reason that RBCs power themselves via fermentation is that they don't have to use up the precious oxygen they are supposed to carry to other ares of the body.

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As far as I can remember, RBC loose their nucleus early in development, and later on most of the other stuff inside them including their mitochondria, aka power-generator.

But RBCs do use glucose as a fuel source kind of like yeast does, by process of fermentation or something like that. I think in fact RBCs are closer to yeasts then to regular other human cells. It requires no insulin to do this, and so it gives a true picture of the blood glucose levels, what finger-sticks do not since insulin can and does influence them. So it does take up glucose, and thus the A1C give you a picture of the amount of average glucose that RBCs are exposed to during the 120 days that they are alive.

Okay, I'm with you on the development of RBC's - they are generally speaking, just big SACS that carry around heme molecules. And yes, they use glucose but anaerobically so as to spare the O2 that they carry (and by default since they don't have any mitochodria to perform aerobic respiration). But still - how did the glucose GET INTO THE CELL WALL - its still a barrier membrane and insulin needs to be there to let it in, doesn't it?

Are you suggesting that by losing the other organelles that this changes the permeability of the RBC membrane allowing glucose to come in as it will?

(Pity my instructors - they routinely get three page emails from me after a lecture - on a good day its only one or two questions - my norm is usually about 10!!) :rolleyes:

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Specializes in ICU, Psych.

Not sure how it happens, I would have to dig out my A&P or Gen.OrganicBiochemestry book and look it up..sorry

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Ah, I knew I should have had organic chem - my AP book was a dead end on that - have done some intense googling on it too and can ONLY get information "what it measures" = not so much the process of how it got in there the first place to be measured!

Thanks tho' for some thoughts on it. :up:

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Okay, I'm with you on the development of RBC's - they are generally speaking, just big SACS that carry around heme molecules. And yes, they use glucose but anaerobically so as to spare the O2 that they carry (and by default since they don't have any mitochodria to perform aerobic respiration). But still - how did the glucose GET INTO THE CELL WALL - its still a barrier membrane and insulin needs to be there to let it in, doesn't it?

Are you suggesting that by losing the other organelles that this changes the permeability of the RBC membrane allowing glucose to come in as it will?

(Pity my instructors - they routinely get three page emails from me after a lecture - on a good day its only one or two questions - my norm is usually about 10!!) :rolleyes:

Granolagirl17,

According to my pathophysiology text (Porth's "Essentials of Pathophysiology") glucose entry into erythrocytes is not insulin-dependent. It apparently diffuses into the red blood cell just like oxygen does. Excellent question, by the way.

notadoc

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You know, its hard to look this stuff up online when you don't know how to ask/phrase the question - so I followed up on your post and started looking into diffusion of glucose into RBC's. Got me down the right track! :up:

Your response still left me wondering as to if/why/how the membrane was so different and wouldn't it need to be HUGELY permeable or fairly different in its structure if glucose could just freely diffuse in and out - what would

keep other things from doig the same - or is it just a big open sac?

Eventually lead me to.... GLUT1 - a glucose transporter that is found

in highest levels in adults in erythrocytes and also in the

endothelial cells of barrier tissues such as the blood-brain barrier. (From Wikipedia) : GLUT1 behaves as a Michaelis-Menten enzyme (whatever that is) and contains 12 membrane-spanning alpha helices, each containing 20 amino acid residues. A helical wheel analysis shows that the membrane spanning alpha helices are amphipathic, with one side being polar and the other side hydrophobic. Six of these membrane spanning helices are believed to bind together in the membrane to create a polar channel in the center through which glucose can traverse, with the hydrophobic regions on the outside of the channel adjacent to the fatty acid tails of the membrane.

AHA! Victory! Now I can get some sleep! :)

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