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Significance of White Blood Cells, Understanding Your Lab Tests

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Published on September 17, 2014

What are granulocytes, and what do they have to do with your white blood cell count? Laboratory scientist Dr. Susan Leclair helps us understand the function of some white blood cells (WBC), how they are counted, and how strenuous activities or injuries can impact your lab tests results. What time of day is best to test your WBC count? Dr. Leclair explains.


Transcript | Significance of White Blood Cells, Understanding Your Lab 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.

Hi.  I'm Professor Susan Leclair.  I'm a chancellor professor at the University of Massachusetts Dartmouth, and I've been involved for many years now with patient listservs that try and explain to patients and their caregivers about their diseases and about some of the laboratory tests in particular that go along with them.

So today I'm going to answer a couple of questions that people have written in to Patient Power on what are some of the white cells that you hear talked about and are concerned with and how they might vary in their test results.

So the first thing that we're going to talk about are granulocytes.  The first thing that I have to tell you about them is that hematology is a relatively young profession. And as a consequence, we don't have quite the rigidity of nomenclature that other kinds of medicine do.  So granulocytes are also known as neutrophils. They're also known as basophils and eos because all of those cells contain granules.

Neutrophils are by far and away the most common of the white cells.  They contain—well, kind of, like obviously, neutral granules, but there's usually around 60 to 70 percent of the white cells in your peripheral blood are neutrophils. And so as a consequence, we sometimes call them granulocytes because they're the dominant cell that has granules in it.  I know, it's a pretty sad thing.

So what do granulocytes do, and one of you asked a question about white cell counts having to do with granulocytes, so let's see what happens.  Granulocytes are made in the bone marrow.  They then leave the bone marrow and get out into the peripheral blood, but eventually something's going to happen, and they will leave the peripheral blood and get into the tissues.

So if you wanted a total granulocyte count, you'd have to count all the cells in three different places: in the blood, in the tissue and in the bone marrow.  We don't do that.  We count only the ones in the peripheral blood, and even that's a little bit of a lie.

There are two places that cells can be when they're in the bloodstream.  The first one is in the circulation itself.  The other one is up against the wall, so-called marginating.  And all you have to do is think of the 7th grade dance to remember what boys are like. There's one or two in the middle of the room, and all of the others are marginating up against the sides of the gym walls until somebody drags them into—or onto the floor.

We only count the circulating cells.  But if you want to, you can knock the marginating cells off the walls, and that's not as hard as it sounds.  You want to raise your white count, you want to raise your granulocytes, run up the stairs before you have your blood drawn.  You want to be stressed before you have a blood tests. It's going to raise your white count.  You do any exercise, it's going to raise your blood count.

When—as any woman who's ever had a child will tell you—labor tends to be strenuous exercise, and every woman for 24 hours after delivery of a baby is going to have a white count that's 20,000 or maybe 25 because all of those marginating cells have fallen off.  It's going to take them about 24 to 36 hours. They'll all go back onto the walls of the vessel again, so your white count drops.

So sometimes changes in white counts just happen because you had a fever.  You were afraid, so it's an adrenalin rush.  You ran up the stairs because you were late.  You had some sort of trauma or bruise, and all of that is going shake those marginating cells off into the peripheral blood.  And it really doesn't mean anything.

When you look at the marginating cells, they're functional cells. They're just as good as the ones in the center of the circulation.  It's just that it's easier for them to be up against the walls because they're going to do their work outside of the blood vessels in the tissues.  So they're just hanging around those walls waiting for something to happen.

Something like a dead and dying cell, we all have them. They're all dying every day.  You cut a paper cut, you fell down a stair, you got something seriously wrong with you. It doesn't make any difference what the damage is.  If there's a damage, those white cells are going to come out of the bloodstream and get into the tissues. They're going to do two things.  They're going to clean up the dead and dying stuff, and they're going to defend you against whatever foreign elements like bacteria or viruses are in there.  So they have to get out, and they have to get out quickly.

One of the slides here shows that that that's what kind of happens.  All these cells that are in the circulating blood now are just moving out to the margins, and then they're moving out of the bloodstream itself and migrating over to where in this instance a rather nasty-looking pin looks like

And that's going to take a little bit of time to do. It's part of the inflammatory response, so this goes along with the redness and the heat and the swelling that goes along.  And then all of these cells are going to reach out, and they are going to find the foreign material.  The slide on the left is a scanning electron microscope. It looks threatening, I know, it literally is moving across a solid surface to attack the bacteria that's in the front of the slide.

So that means that when these cells get into this area, and they eat this bacteria or a virus or whatever it happens to be, they will die in your service, by the way, and that collection of dead and dying cells is called pus.

So you can see kind of a connection here.  As you need more cells to come into an area, they're going to be leaving the bone marrow.  They're going to be coming out into the peripheral blood.  They're going to be moving out into the tissues so that the white count will be in the beginning maybe a little low as the cells all move out into the tissues to be replaced by newer cells that are coming out of the bone marrow to replenish it.  So there's an ebb and a flow to these white cell counts.

There's also an ebb and a flow to the white cell counts during the day.  You get up in the morning, you're a little on the stressed side.  It's actually one of the highest times of the day for internal and emotional stress.  Your white count's going to be a little bit higher.  You're at home, it's the end of the day, your boss hasn't yelled at you, the world is good, you have dinner in front of you and a pleasant night ahead of you, your white count's going to drop.

So there will be that ebb and flow that occurs there, too, and that's important to know because some of you over the years have asked, when should I get my blood test taken? And the answer is at the same time every day.  I don't care when.  I only care that if you started at 8 o'clock in the morning, you should probably continue going at 8 o'clock in the morning.

If you started at 4 o'clock in the afternoon, you should end somewhere around 4 o'clock in the afternoon because that way there's a consistency to your physiology that the physician can be comfortable knowing that this white count change or not change is not dependent upon the fact that you changed your eating habits or that you did something that un—that was out of the ordinary.  So try and keep it as consistent as possible.

When you look at these cells, too, you'll find that some of them are younger or older than they should be.  The typical white cells that are in your peripheral blood fully functional, fully mature.  They come in two forms as granulocytes.  They come as something called a polymorphonuclear, or PMN.  They have a segmented nucleus, so sometimes people call them segs to add to the grief.

And then there's an ever so slightly younger, kind of like the difference between an 18-year-old and a 25-year-old.  Fully functional, maybe not as bright, not quite as experienced but still is going to be able to get the job done.  And that's called a band.  The closer or—that you get to the band form or the more frequently you see the band form means that there's a need that's kind of stressful, but your bone marrow isn't capable of making an entirely fully formed 25-year-old, and they're sending out the 18-year-olds instead.

Other than that, there's really no functional difference between bands and polys, or segs and nonsegs or neutrophils and bands and all those other names. They're just a way of kind of keeping score on things.

Okay.  So, now, remember, if you have any questions, and I hope you do, please send them to  And remember that knowledge sometimes is your very best medicine. 

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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