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Understanding White Blood Cells and Differentials

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Published on March 11, 2015

“What's the change between the numbers you had before and the numbers you have now?” Dr. Susan Leclair talks about white cells counts and what types of activities have an impact on your numbers. She walks us through how the cells are counted, how agitating cells can increase numbers, and what exactly experts are really looking for. Watch as Dr. Leclair explains the differences between manual and automated differentials and the instruments used to count the cells.


Transcript | Understanding White Blood Cells and Differentials

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, hello again. This is Professor Susan Leclair from the University of Massachusetts Dartmouth, and today in this continuing series I'm going to talk about white cell counts and differentials.  And I know several of you have written in about how can you tell, how do you interpret what's going on about these.

I think we mentioned that the white cell counts, I think it was the very first of these sessions, will vary during the day, and it will vary during—blah-blah—and it will vary due to your emotional and physical state.

Again if you've been driving in a rainstorm and the car on the other side of the road hits the puddle before you do and that puddle splashes all over your windshield—well, first you duck, but secondly the reason that you duck and the reason that your heart rate is going and the reason that you're having trouble breathing is that adrenalin surge that comes from fear and an unexpected reaction.

So, yeah, you're not sure this is the phlebotomist that you want, you had a fight with your spouse before you got to the lab, the traffic was a bear, all of that stuff is going to influence the white cell count just like having done maybe 20 minutes of yoga and coming calm and serene is going to influence it in the other direction.  So white counts will bounce around a lot.

I also should say that laboratory counting methods are good, but they're not perfect.  If I get a sample of blood from you and I run 10 white cell counts on that very same tube of blood, I am not going to get 10 identical answers.  I'm going to get them close, 5.4, 5, 5.7, 6, 5.2, 5.1.  They'll all be around and close to the number that is the actual number, but they will not be produced in a repeated identical order.  There will be a range of maybe plus or minus .5 of the real one.

So don't worry if your physician, as they frequently will do, will look at a number, well, last time it was 5.5 and this time it's 6.0, and that's gone up you think, and he says, aah, don't worry about it.  That's part of the reason he's saying that.  He's saying that because it's not a significant rise in your white blood cell count.

And if you did have one of those days when you were late and you were frustrated and the world was against you—I have those frequently—and you get up there to have your blood drawn and things don't go well, yeah, maybe it can go from a 5.0 to maybe a 7.5 or an 8, because you've done a lot to those cells to cause them to become agitated. When you're upset, they're upset.

So just kind of keep in mind that you're looking for kind of an overall trend, and big numbers are significant, less than maybe .5 means no change whatsoever.  Less than 4.0 means a little problem, but I bet you it was something psychological or relatively minor to deal with.  So that takes care of the total white cell count.

Then there's two ways to figure out what cells you've got. The older, the traditional, the one I love takes a drop of blood smears it out onto a slide, that's why it's called a blood smear.  It stains so that we can see these cells, and somebody with some skill and some knowledge sits down at a microscope and evaluates those cells.

There are thousands of cells on that slide. We cannot evaluate all of them.  So we randomly pick 100 cells because, well, that works out well for percentage.  If you've got a really high white count, we might do 200 cells in order to increase the yield of accuracy.

But we're concerned about quality.  What do these cells look like?  Do they have holes in them because something is eating them?  Is there something wrong with your nucleus that makes them look funny?  Are they bigger than they should be?  Are they smaller than they should be?  Are they staining correctly because that tells you something about the metabolism of the cell.  So this is a real qualitative kind of assessment of these cells.

Do you get a number?  Sure.  You get 60 percent polys 40 percent lymphs.  Or you get 59 percent polys and 39 percent lymphs and 2 monos.  That's the kind of differential you get.  And when you look at your report form, it will have a percentage sign next to it to let you know.

The problem with this percentage differential is that if you have, say, 75 or 80 percent polys—we're only counting a hundred cells—by definition the lymphocytes must go down, because you only have 25 left cells to count.  So an increase in one cell line will—must—absolutely, positively must cause a decrease in the other one.  So sometimes you're going to look at number and go, oh, my god, my lymphocytes are down.  No, it's because your granulocytes are up.  Or my granulocytes are down.  No they're normal.  It's because your lymphocytes are up.

So one of the problems with the percentage differential is you can be misled sometimes by which cell is causing the problem.  Why do I love the percentage differential? Because I get to sit at a microscope and look at the cells.  I tend to root for them, they tend to speak to me—I know, it's a sad life, but they do, and so I like to look at them to see what's happening to the granules, to see what's going on inside them, because that's telling you information that you're not going to get any other way.

The absolute differential count we never used to do until we got the multi-channel instruments.  What the multi-channel instrument will do is it will count the number of cells, okay, so you get a total number of white cell count, but they will also evaluate the size and the shape of the cell, kind of like the mug shots you get from the police station.  You get a front-on view, like this, so you see how fat my face is or what color my face is or something that's to do with that. And then you get the profile that lets you know is anything lumping out of it.  

A lymph has no granules so a lymph is going to be very flat, so you're going to see this when you look sideways, and you're going to see this when it looks frontways. A granulocyte's got, well, granules.  So when you turn it from this to this it's got lots of lumps and bumps that are coming out, because it's got all those granules in them.  So we can differentiate them by this machine.

A machine does this very fast.  So they don't count a hundred cells.  These machines will count anywhere between 20,000 and 50,000 cells.  Okay.  Now you get a really good sense of what cell is increased and what cell is decreased, because the machine is going to tell you in 50,000 cells I counted 25,461 granulocytes and whatever the math would be to finish that in lymphocytes, so you get an absolute cell count.  And that's wonderful because that eliminates the percentage differential's problem with misleading information.

What's the problem with the absolute differential?  You don't look at the cells.  The machine cannot look at these granules inside the granulocytes because remember, all they're looking for is lumps and bumps, and say, I think there are too many.  I don't think there are enough.  I think the granules that you've got are too small, or they're too big.

In the case of the neutrophil, you have four different kinds of granules.  That machine can't tell the  difference between those granules, but sitting down at a microscope I surely can.

So when do you want to do a manual versus an automated differential?  Well, the automated is going to come all the time because that's what a CBC includes now.  You should do a manual differential if the white count has changed a lot, you're not feeling well for some reason, the numbers that come out of the automated differential look suspiciously different than before.  In a laboratory we call it a delta.  What's the change between the numbers you had before and the numbers you have now?

So we have on January 1 you had 60 polys, 40 lymphs and on February 1 you had 75 polys and 20 lymphs, I'd probably want wouldn't bother.  It's not worth it.  So it has to have a big enough delta, a big enough change for you to want to be able to see what's going on in these cells, and how can they handle it.

For automated differentials there are two kinds of instruments.  One is going to give you neutrophils, lymphocytes and something called MID, minimal size cells.  That's everybody else.  So you get lymphs, you get granulocytes, and you get a third category of eos, basos, monos and anything else that happens to go in there.

The expensive machines give you polys, granulocytes. They give you lymphocytes, monos, eos and basos. So you have your chance to get a five-part differential that gives you a little more information. 

Hope that made sense.  Instrumentation sometimes can be kind of a funny topic. So if you have any questions, please write to us at  And remember, knowledge is an important thing.

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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