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And the Band Played On (Leukocytes #1)

Posted by Frederick Wasti
Nov 04 2013

When I was at Dana-Farber in Boston for blood testing and treatment on 9/16, I was a bit surprised to see some of the results of that day's blood testing. Here's what I saw:

The ~Complete~ Blood Cell Count seemed to be more or less normal -- WBC Count = 7.4 (in K/UL, or thousands of cells per microliter), RBC Count = 4.59 (in M/UL, or millions of cells per microliter), Platelets = 120 (in K/UL, or thousands of cells per microliter), while the "REFERENCE" column showed the "normal range" of each measurement. [And, yes, my platelet count was a bit low, but that's pretty common for me nowadays, and it's been moderately low for some time now -- I guess, for me, it's "the new normal" -- but, in any event, the Complete Blood Cell Count numbers were not surprising.]

It was the ~Differential~ White Cell Count numbers that seemed a bit unusual (at first), at least in how they were expressed.

Now, if you're a regular reader of this blog, and/or you know at least a little bit about the different types of white blood cells (but, as with me, "maybe not too much"), the terminology used in the above report might be a little confusing and/or surprising. You might say "OK, I can figure out the abbreviations for Lymphocytes, Monocytes, Eosinophils, and Basophils, but where are the Neutrophils?", and/or "So, what the heck do Band, Poly, and Meta mean?". Of course, at that point you might have then guessed that Band, Poly, and Meta likely refer somehow to neutrophils, and you would indeed be quite correct (Congratulations!). You have maybe already noted that, if you add the Band, Poly, and Meta percentages together, you get 98%, which is about what my neutrophil count usually has been for many months now.

But, just exactly what ~are~ Bands, Metas, and Polys (as the plural of Poly is usually spelled in hematology, rather than "Polies"), and just how are they related to neutrophils, and what's with the "-A" and "-M" suffixes? Well, those questions are just what this blog entry, and the next two, are all about.

Let's take the easy question first - let's take a look at the "-A" and "-M" suffixes. (Maybe you've guessed correctly already, and this will just confirm your hunches). As it turns out, "-A" stands for "auto" or "automatic", while "-M" stands for "manual" - not as in automatic or manual transmission, of course, but as in automatic and manual methods of counting blood cells.

For an ~automatic~ blood "count", a beam of light is passed through a small sample of blood (in a very thin clear tube), and then a special light sensor and some nifty computer processing are used to estimate (with surprising accuracy) the number of cells of each type, without actually counting any cells at all. [If your response to this brief description is "So how dey doo dat?", well, it's actually quite clever and also (I think) pretty interesting just "how dey doo dat", and so it will be the subject of a future blog entry...]

In contrast, for a ~manual~ blood count, a trained technician examines a "blood smear" (a thin film of blood) under a microscope, looking at the first 100 white cells he/she finds, and records how many neutrophils, eosinophils, basophils, lymphocytes, and monocytes are seen -- then, the number found of each type, out of 100 cells counted, is considered to be the extrapolated percentage of each type in the blood.

So, looking back at the blood test results from 9/16 quoted above, it would seem that my differential white cell count for that day was performed manually. (There is nothing unusual about how my cells are counted on any particular Dana-Farber day - sometimes they're counted manually, and sometimes they're "counted" automatically.)

Of course, if my cells are to be counted manually, a blood smear has to be properly prepared to start with. Two microscope slides are generally employed to make a blood smear - one will have a drop of blood on it, and the edge of the other will be used to smear the drop into a thin film. Note that the smear involves ~pushing~ the drop away from the technician, and not sliding the drop towards him/her:

[Amongst my many jobs and "careers" (<grin>), I've taught both biology and human anatomy and physiology at the high school and college levels. Back in the 1970s, it was a normal biology lab activity for students to obtain drops of blood from their fingertips and to make blood smears to examine under the microscope (and to test their blood for blood type and Rh factor). Nowadays, it would be very unusual (and quite inadvisable) for high school students to be handling blood at all, but we weren't overly worried about AIDS (and Hepatitis, etc.) back then. Even after we did become more concerned about the hazards of blood-borne diseases (and stopped using "live" blood in high schools), making blood smears was still a normal lab activity for adults in college (with suitable safety precautions in place, of course). So, I've demonstrated such techniques to students and monitored how students performed them many, many times.]

So, the purpose of making a blood smear is often to determine the proportions of the types of white cells (i.e., leukocytes) -- that's what a ~Differential~ Blood Count consists of.

As you can see in the above image, the five white cell types fall into two groups, "granulocytes" and "non-granulocytes" (the latter often called "agranulocytes" instead, the prefix "a-" meaning "not"). The distinction is based upon whether the cells show specks or granules in the cytoplasm (i.e., the material within the cell that is outside the nucleus). If you look very carefully at the above cell images, you should notice visible reddish granules in the eosinophil and even more obvious blue granules in the basophil, and , if you really look carefully, some faint, small reddish granules in the neutrophil. In contrast, the lymphocyte and the monocyte do not show granules in their cytoplasm.

[If you aren't familiar at all with the various types of blood cells, you might refer back to my post from 4/1/2012 on "Blood Cells 101". Even if you did view that previously, you might still want to take a quick look at it once again anyway, as I very briefly covered the normal proportions and functions of each blood cell type there, and I won't be repeating that info again here, instead emphasizing the ~appearance~ of each white cell type here.]

You may also notice that the nucleus (the darker, more-or-less central area in each cell) can vary in shape quite a bit, and (probably surprisingly to you, if your only familiarity with the nucleus in a cell is from images of generalized cells from "way back" in high school biology) that the nucleus might even seem to be in two or more pieces -- in the granulocytes, the nucleus typically has two to five lobes, connected together by thin filaments (which are not generally visible without very high magnification).

However, I should point out that the colors seen in the granules and in the nuclei in the image above are not real -- in fact, if you looked in a microscope at a blood smear prepared just as described above, you would see something such as the following:

In the above image, there are several dozen red cells (that don't look particularly reddish), and a white cell (of some sort) in the center. And that's the problem involved in looking at such a simple blood smear - white cells really are quite white (or clear, actually), and don't naturally look like the cells in the "granulocytes" and "non-granulocytes" image further above -- so, how can you tell which type of white cell each is?

What is missing inside the white cell in the image just above is a stain that would color the granules and the nucleus so that the otherwise nearly invisible nucleus and granules could provide visual clues for telling which type it is. However, the stain must do more than just make structures visible - it must also act as a ~differential~ stain, one that colors cell structures differently for each of the different cell types. So, a suitable differential stain (which is generally a combination of two or more stains mixed together) is normally added to the blood smear, as shown by the lower smear preparation in the following image:

[Historically, the most commonly used blood stain (and certainly the most commonly used blood stain in science education) has been Wright's stain (named for James Homer Wright, who developed it in 1902), but there are others. (I do not know what stain is used at D-F for performing manual white cell counts.)]

Well, anyway, I've covered in this post how a blood smear is prepared, and why it has to be stained, in order to use it to perform either a Total or a Differential Blood Count. I've provided short answers to questions about the unusual notations from 9/16 (i.e., the Bands, Polys, and Metas are types of neutrophils, and the "-A" and "-M" abbreviations are for automatic and manual counting techniques). However, I haven't yet really got into how the white cell types are (more or less) easily distinguished, nor have I explained exactly what the Bands, Polys, and Metas really represent -- these will be the subjects of the next two blog entries ("Leukocytes #2" and "Leukocytes #3"). Please stay tuned.

In the meantime, I will include a couple of the latest graphs, showing how things are still pretty "boring":

Let the band(s) play on... Thank you for reading along.

Categories: General, Leukemia