When you look at a blood smear, it’s best to have a plan, and it’s best to try to follow it each time.
That might sound boring – but you’ll make a much more accurate and complete assessment that way. Otherwise, the temptation is to just put the slide under the microscope, scan around to see if you see anything weird, and then focus on that (while missing some important features).
There are 10 main things you need to be sure to evaluate on a blood smear. I like to start with the red cells, move to the platelets, and save the white cells for last…but you can come up with whatever method suits you.
1.Red blood cell number
First, make sure you’re in the right part of the smear. You should be a couple medium-power fields in from the “feather edge,” which is the thin edge of the smear where the cells are all spread out and there are huge empty spaces. Just give it a quick glance and make sure the red cells aren’t either piling up all over each other, or spread out too far with lots of holes in between – like the red cells in the image above. Take a look at the RBC on the CBC and make sure it fits with what you’re seeing.
2. Red cell size
Normally, if all the red cells are roughly the same size, your eye won’t be able to tell if they’re microcytic (small) or macrocytic (large). So you have to just look at the MCV for that. What your eye can see, however, is a range of sizes. So take note and see if there are some cells that are smaller, and some that are bigger. If that’s the case, it’s called “anisocytosis” and it should be reflected in the RDW (red cell distribution width) on the CBC. The more anisocytosis (variation in size) there is, the bigger the RDW should be.
3. Red cell shape
Normally, red cells are all nice and round, like the ones in the image above. In some anemias, there are funny-shaped cells, like schistocytes (fragmented red cells), sickle-shaped cells, teardrop-shaped cells, or target cells. Your eye will naturally be drawn to these (which is why you should force yourself to follow a consistent method when looking at a smear – otherwise you just look at what your eye is drawn to!). Take note of whether there are any non-round cells, and if so, describe what kinds of shapes you see.
4. Red cell chromasia
“Chromasia” refers to the amount of hemoglobin in the average red cell. Normally, there is a zone of central pallor (the white dot in the center of the cell) that comprises about 1/3 of the diameter of the cell. Check out the cute zones of central pallor in the red cells above. These cells are called “normochromic.” If there is a huge white dot, and just a thin rim of hemoglobin, then the cells are called “hypochromic.” There really isn’t a “hyperchromic” type of red cell.
5. Reticulocytes
Take a look around and see if you see any polychromatophilic cells (these are slightly bigger than normal red cells, and they have a lilac tinge to them). These are just young red cells whose RNA has not yet been completely extruded (so they stain a bit blue). In normal blood, about 1% of the red cells are reticulocytes (because we’re always making new red cells). That equates to about 1-2 red cells per field. If you see more than that, it means the marrow is kicking out red cells at an increased rate.
6. Stuff inside red cells
Take a look and see if you see any red cells with stuff inside – like nuclei, Howell-Jolly bodies (little nuclear remnants that didn’t get extruded), Pappenheimer bodies (little iron granules), organisms (like malaria or babesia).
7. Platelet number
There should be between 7 and 21 platelets per high power field, which corresponds to a platelet count between 150 and 450 x 109/L.
8. Platelet morphology
This doesn’t usually yield much – but take a look at the platelets anyway and make sure they’re roughly of normal size, and have some nice granules inside. There are rare platelet disorders in which the platelets are abnormally large, or lack granules, or both.
9. White blood cell count
Do a quick scan of a bunch of high power fields and see how many white cells there are. There should be a few white cells per high power field. Check the WBC and see if it seems to correspond to what you’re seeing. Then, do a differential count: count a few hundred white cells (500 is best) and put them in categories (neutrophils, lymphocytes, monocytes, eosinophils, basophils). Compare this to the automated differential on the CBC, and multiply the percentages by the total WBC to get the absolute counts of each cell type. When you’re trying to determine if a patient has a normal number of a certain cell type, absolute counts are much more reliable than percentages.
10. White blood cell morphology
Finally, check the morphology of the white cells. You’ll probably do this as you’re doing your differential – your eye will be drawn to any abnormalities as you’re classifying the cells. Make sure the neutrophils and lymphocytes look normal, and keep your eye open for any weird-looking cells like blasts or circulating carcinoma cells.
Whatever order you decide to use, if you do it the same way each time, it will start to become automatic – and you’ll be much more likely to do a thorough, accurate job.
very useful info.. thanks!
The info is quite useful and very practical. It has just solved a problem sometimes face; it is really true that when you follow the steps above it becomes automated in examining a blood smear. Thanks!
Practical steps to follow for blood smear reading,
Nice staff
Very good
thanks for all
v.nice work.
I never thought it could be that easy….
I never thought it could be that easy…. Thanks a lot.
Very nicely explained. Two comments:
1. Spherocytes are usually dark stained and hence hyperchromic.
2. I wouldn’t bother doing a manual differential unless there are abnormal white cells present (eg, myelocytes, b;asts) or I thought the automated diff was incorrect.
I agree with your comments. Spherocytes do appear dark in color, and therefore might be loosely called hyperchromatic. However, since they don’t have an excess of hemoglobin in them, they aren’t truly hyperchromatic in the strict sense. I agree, too, that if you have an automated differential, a manual differential is only necessary if there are abnormal white cells present, or if you think the automated diff is incorrect.
usefull info
useful info in haematology manual confirmation procedure…
very useful heamatology info especially in doing manual confirmatory peripheral blood smear ..~
Lovely thanks.
very useful
Very simple yet concise summary of peripheral blood cell morphology.
Students must notice the usefulness of adequate area on smear for red cell morphology as well as of absolute count (rather than a middle step called DLC).
One thing to ask is the source of counting platelet 7-21/HPF and their correspondence with an estimate of platelet count/L.
Thank you so much.
thanks for all, what do you mean in few WBCS /HPF You estimate ? thanks alot.
Normally, you see somewhere between 2 and 6 white cells per high power (400x) field. You should count a bunch of fields – maybe ten – and take the average just to be sure you avoid sampling error.
nice work. well said.
i like the order….it gives a systematic way of reading a blood film and what to comment on. great work
very useful. simple points but very important
Nicely explain
oh very useful thing.Please can you tell me is there any training center in middle east wherewithal blood training.i am very much interested
When calculating the absolute lymphocyte count do you include both lymphs and reactive lymphs from the differential or do you leave out any lymphs classified as reactive/atypical? If you leave out reactive atyp could you explain why?
People do it differently! I’d do both 🙂 When counting, I’d separate out the reactive/atypical lymphs, and then I’d calculate the absolute count both for total lymphocytes (normal plus reactive/atypical lymphs), and for reactive/atypical lymphocytes. That way you know both how many lymphocytes are present, and how many reactive/atypical lymphs are present. There isn’t a specific cutoff for how many reactive/atypical lymphs you need to see in order to make a diagnosis – but obviously if most lymphocytes are reactive/atypical, that is more meaningful than just a scattered reactive/atypical lymphocyte here and there.