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Making a Great Blood Smear

Making a great blood smear is an important skill for every technician and assistant, even if your hospital does not require differentials to be done on a regular basis. You never know when you may need to take a quick look to make sure platelet number is adequate, scan for blood parasites, or do a full differential if your analyzer is down (or you don’t have one!). It is a good way to impress your boss also; it seems in this age of hematology analyzers, reading a differential is getting to be a lost art. Plus it is a lot of fun! And it all starts with the great blood smear.

Figure 1: Get a new, unused slide and get ready. Figure 2: Place a very small drop of blood at one end. The ideal blood sample is directly and immediately from the patient. Anticoagulant can sometimes distort some cells.

Fig.1   Fig.2

Making a smear requires a very smooth motion, continuing to the end of the slide even though the smear should end about ½ to 2/3 of the length of the slide. The smear itself should look very smooth with a seamless progression to what is called a “feathered edge”. This is the very end area of the smear and consists of a monolayer of cells. The monolayer will contain cells that are the easiest to identify and are the least distorted. This is the area on which you will concentrate your analysis once the slide is stained.
If your blood sample seems thin (can occur with anemic patients), increase the angle of the slide you are using to smear with; otherwise your smear may run right off of your horizontal slide and you will not have a nice feathered edge, and your smear will be so thin you will have trouble finding enough cells. If the blood sample seems thick (can occur with dehydrated patients), decrease the angle of the slide to create a thinner smear; otherwise you will have cells piled on top of each other rather than a nice monolayer.
If your smears are really thick and take up the entire slide, you are probably just using too much blood. It really needs to be a very small drop.

Try not to get impatient with yourself; it takes a lot of tries to finally perfect the motion. Practice, practice, practice! Allow the blood smear to completely dry, and then use diff-quick to stain it.

Figure 3 and 4: Dip your slide slowly in stain #1, the fixative.

Fig.3 Fig.4

Figure 5 and 6: You should count a slow "1001" for dip #1, "1002" for dip #2, for a total of 5 slow dips. Then tap off excess liquid.

Fig.5 Fig.6

Figure 7 and 8: 5 slow dips in eosin stain #2, then tap off excess liquid.

Next, it's 5 slow dips in new methylene blue based dip #3; tap off the excess liquid.



Figure 9: Rinse both sides with tap water. Figure 10: Allow to air dry. Or, if you are impatient like me, use a hair dryer on low.

 Your blood smear is now ready to be read.