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A Look Inside the Bone Marrow: Understanding Red Blood Cell Index Tests

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Published on April 12, 2015

The red cell index provides physicians a large concentration of data.  Which is of greatest importance to you, the patient?  Dr. Susan Leclair explains mean cell hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and red cell distribution width (RDW).  Of these three, RDW in combination with MCV is of particular importance when interpreting your indices’ values.  Using basic math, Dr. Leclair descriptively illustrates how these blood tests tell the story of what is happening deep inside your bone marrow.

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Transcript | A Look Inside the Bone Marrow: Understanding Red Blood Cell Index Tests

Please remember the opinions expressed on Patient Power are not necessarily the views of our sponsors, contributors, partners or Patient Power. Our discussions are not a substitute for seeking medical advice or care from your own doctor. That’s how you’ll get care that’s most appropriate for you.

Dr. Leclair:

Well, welcome back.  We're going to continue with the indices.  And although I spent a long time on the MCV the last time, we're going to go through a couple of these relatively quickly.

The MCH, mean cell hemoglobin, how much hemoglobin does every cell have?  If I have 16 candies and they all weigh one pound, how much weight—not volume now, slightly different—how much weight does each candy have?  Not enough, so you're going to have to eat more I suppose.  So it's kind of straightforward.

How much hemoglobin is in each cell?  High is of no real importance.  Normal is nice.  Low, you're having trouble making hemoglobin.  So now we're back to iron, anemia, chronic disease, exposure to heavy metals and thalassemia.  So that one's not really as important as some of the others.

The MCHC used to be the only thing of value that the indices really gave to physicians back in the day of the spun hematocrit.  It is less important now, and it has to do with the ratio between the red cell and the amount of hemoglobin, so I'm not going to spend much time on that.

The one I am going to talk about is the RDW, red cell distribution width.  It's relatively new.  Strangely enough, Max Wintrobe did not invent it, and it came because of those multichannel instruments.  We want all of your cells to be monotonous in size.  Matter of fact, they should vary less than one micron in diameter, from the oldest to the youngest.  So when you look at them in a microscope, what you should see, like this picture, it shows you really they look like a lot of dimes strewn around on a screen.

But look at this next one.  You see big cells, you see small cells, you see broken ones, you see oddly shaped ones.  That's a change in size, but it's also a change in breadth of size.  So now what I'm looking for in the red cell distribution width isn't what's the average, it's what's the stretch on this.  If I have a mixture of oranges and apples and I take an MCV of that, I get a volume size of that.  It will probably be a pretty accurate volume, because oranges and apples are about the same size.

But supposing I have a bunch of fruit.  There's a watermelon and a cantaloupe and a banana and a grapefruit and figs and grapes and raisins.  Can I give you the average size?  Yes, I can. Does it mean anything?  I mean, I know I can give you the math. That's really easy, but does it mean anything?  Is there value to know that the average size of a population of fruit that goes from a raisin to a watermelon is whatever it happens to be? Probably not.

So the more variation in size your red cells have the less reliable the MCV is.  Because if all of your cells are large, well, then I'm going to get a pretty accurate MCV.  If all of your cells are small, I'm going to get a pretty accurate MCV. 

But what happens if you have teeny, teeny, tiny red cells, but you also got three units of blood yesterday so now you have half of the blood or maybe 20 percent of your blood is now these normal-size cells?  Does the average make sense?  Should I follow it to any degree?  Is it important in any way?  Well, no. The answer has to be I really can't depend on it as much as I could because I have more than one population of cells.  I have a mixture here.  Gee, if the RDW is going up and the MCV I'm not really too sure of, then maybe I should lean more back to a hemoglobin from several talks ago, because at least that's not going to change with the size of the cell.  I can weigh the amount of hemoglobin that I've got.

So if the RDW increases, I'm going to rely less on the MCV, possibly less on the hemoglob—on the hematocrit and more on the hemoglobin.  So when you hear people talk about, well, my hemoglobin was this but my RDW was that and what does mean, RDW means variation.  It's like taking the average height of a population of people ranging from the tallest man in the world to a 2-day-old baby and finding the average.  Or maybe taking all of the professional basketball players and finding the average—much closer set of values, much more reliable set of information that I'm getting.

Typically, the RDW rule is you should always have a little because you're going to have cells that are brand new—those retics—cells that are really old—ones that are going to die in the spleen—so you should have a little bit of an RDW, you. But as the RDW becomes increased, what it's saying to you is there's stress in the marrow.  I don't know what kind of stress. I don't know how long you've had it or why you've got it. But I can tell you there's stress, and the higher the RDW the more stress that's going on.  One rule of thumb is once you get an RDW over 20 or 22, somewhere around like that, you should either do a manual hematocrit, that old reliable Max Wintrobe put it in a centrifuge and spin it. Trust me, nobody's going to do that—or just rely on the hemoglobin because that hematocrit's not going to be as accurate as you want it to be.

Maybe that's a minor point. And maybe I'm belaboring these indices, but there's so much information. There's so much that physicians rely on these indices you kind of need to know how to interpret them.  The MCV is going up.  Is that a good thing or a bad thing?  I don't know.  Where did you start?  Is the RDW going up?  That's probably going to be less good.  Is the RDW coming down, but the MCV tends to be floating upwards?  Well, maybe you had small cells, and now your red cells are becoming  more normal size and more consistent.  That's a good sign.  So just taking the numbers by themselves, while it's nice to follow on the spread—the Excel spreadsheet that I know you all have, I want you to pay attention that these two go together, that the MCV and the RDW give you information about not only what the cell range of size is but a sense of how your bone marrow is coping with whatever is causing this stress.

I hope that helps.  If it doesn't, don't forget, send me questions at questions@patientpower.info.  And hopefully this bit of information like the other stuff is going to make you a more informed and more powerful patient in the healthcare delivery system.  Till next time, see you later.

Please remember the opinions expressed on Patient Power are not necessarily the views of our sponsors, contributors, partners or Patient Power. Our discussions are not a substitute for seeking medical advice or care from your own doctor. That’s how you’ll get care that’s most appropriate for you.

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