Here’s a quandry you may find yourself in soon, if you have a habit of sitting at the multiheaded scope down in hematopathology.
You’re looking at a bone marrow smear, and you can differentiate between some of the myeloid cells (blasts have a high nuclear-cytoplasmic ratio; segmented neutrophils are all mature with their multilobed nuceli; metamyelocytes look kinda like mature neutrophils only with a more horseshoe-shaped nucelus.)
But two cells will give you gout or a migraine if you don’t learn a couple simple facts: promyelocytes and myelocytes. How are you supposed to tell them apart, when they can look quite similar? They’re both kinda big, they both kinda have granules…so what gives?
Let’s do a little pre-test here to see what you think about these cells, before we discuss the “official’ way of distinguishing between the two. We can leave the lymphoycte and the red cell precursors out of the discussion (top of the slide). But what’s your diagnosis on cells 1, 2, and 3? Are they promyelocytes, myelocytes, or a mixture of the two?
Here’s the morphologic criteria from my path residency (and my histology course as a medical student) that we used to differentiate between promyelocytes and myelocytes:
- The promyelocyte is the biggest cell in the neutrophil series.
- It also has huge, dark purple, primary (azurophilic) granules both in the cytoplasm and overlying the nucleus.
- However, it does NOT have the beginnings of secondary (specific, pink, salmon-colored) granulation! If you see any of that (even just a little blush of it in the cytoplasm), you HAVE to call a myelocyte.
So for our cells above:
- Cell #2 is a pretty spectacular promyelocyte. It’s huge, it’s got tons of dark granules, and no specific granulation. It does have the beginnings of a little “hof” (a clear zone next to the nucleus) but that should not be confused with specific granulation.
- Cell #3 is pretty clearly a myelocyte. It’s a smaller cell, and there are very few azurophilic granules left; the cytoplasmic granules are mostly just pale, specific granules.
- Cell #1 could be a bit of a challenge because it’s a rather large cell, with abundant dark purple granulation…but it also has the clear beginnings of specific granulation in the cytoplasm. So this cell should rightly be classified as a myelocyte. It’s a pretty early one, for sure – but the presence of the specific granulation pushes it into the myelocyte category.
As a medical technologist in hematology, I was taught that a Promyelocyte must have BOTH granules and nucleoli. If both are not present it is a Myelocyte. Also, if unsure, call mature.
Hi Cindy – Thanks! That’s a great tip 🙂 Also agree with the “if unsure call it mature.” I learned a LOT from the MTs when I was a resident – I’m so grateful that they spent so much time teaching me.
Promyelocytes do not have to have nucleoli. They may or may not have prominent nucleoli. If they are present, you definitely know you don’t have a myelocyte then. The rest of the information list about the granules is perfect. Thanks for all of your information. I am an MT and love all of the interesting facts you give that we didn’t get in school.
Very helpful rightnow as i am doing an EQA slide in my lab.
Right on Cindy. I was also taught that the most distinguishing feature between a myelocyte and a promyelocyte, is that the latter has nucleoli in addition to the other features mentioned….. large cell with dark deeply staining granules.
I’m going to have agree with the granules being the most important. I’m also MT and I’ve come across many pros that didn’t have distinct nucleoli… I learned over the years to focus on the primary and secondary granulation as a distinguishing feature.
Hi Cynthia – Yes!! I totally agree. I remember learning that if you see any secondary granulation at all, it’s a myelocyte. It’s funny how things stick with you – it’s such a visually appealing field, so maybe that has something to do with remembering details. Thanks for your comment 🙂
Boy, I thought Cell #3 would be a metamyelocyte, with its specific granulation, smaller size and especially the indented nucleus, but in your explanation you indicate it’s a myelocyte. Can you clarify for me, please? Thanks, Dr. Kraft, your site is amazing!
Are myeloblast characterizes by a lot bigger nucleus? That’s why I would have said why Cell 3 is not a myeloblast.
Are myeloblasts characterized by nucleus which is a lot bigger than the others? That’s why I would have said why Cell 3 is not a myeloblast.
The cell number 3 looks like metamyelocyte ? Or am i wrong
To my eye, it looks more like a myelocyte. I’d need to see a little more of an indentation in the nucleus to call it a metamyelocyte. But that’s just me! Cells mature on a continuum…they don’t just suddenly change from one stage to the next. And this one does have a tiny indentation in the nucleus – so you’re right to question whether it’s actually a myelocyte or a metamyelocyte. For me, I think it’s closer to a myelocyte than a metamyelocyte – but another pathologist might think that indent is enough 🙂 These are the lovely discussions you get to have when you’re an academic hematopathologist!!
Great piece of information, but I think the image #3 is metamyelocyte because I see the nucleus is a bit indented too or I’m wrong?
Thanks for your comment Ntiamoah! You’re right – there is a slight indentation in the nucleus in cell #3. I still favor it for a myelocyte (because the indentation is pretty small, and for a really classic metamyelocyte you’d like to see more indentation) – but I think if you showed this cell to several different people, some would say myelocyte and some would say metamyelocyte! You bring up a good point, which is that these cells don’t just jump from one stage to the next! So there are going to be cells that seem like they are in between different stages. Maybe we could agree that this cell is somewhere in between a myelocyte and a metamyelocyte! There will always be some cells that you can’t identify absolutely positively for sure – and a good thing to do when that happens is to look around the blood smear for a while and get a feel for what the different cells look like. Then you can go back to the cell that was bugging you (use a marker to circle it on the bottom of the slide first, so you don’t lose it!!) and see if your opinion has changed.