Blood Smear Preparation Guide

Study Notes

Smears are made by placing a drop of blood on a clean glass slide and spreading it with another glass slide at an angle.
The slide is stained and viewed microscopically.
Proper smear preparation needs clean slides, and a proper sized blood drop.

Place a 2-3 mm drop of mixed whole blood approximately 1 cm from the right edge of the frosted area of the slide.
Hold a spreader slide between your thumb and forefinger of your right hand.
Place the spreader slide onto the slide, in front of the blood drop.
Pull the spreader slide back until it touches the blood drop.
Spread the blood by capillary action to near the edges of the slide.
Push the spreader slide forward at a 30-40° angle, using a rapid, even motion. Only use the weight of the slide, do not press down. Spread the blood quickly; otherwise cell distribution will be uneven.
The blood will create a thin film in the shape of a bullet or tongue, with a feather-edged border.
Label the frosted edge with patient information (name, ID#, date.)
Allow the smear to air dry completely before staining.

Should be thick at one end and taper to a smooth rounded feather edge or tongue shape.
The smear should occupy about ⅔ of the slide area.
Should not touch the edges of the slide.
Should be free of margins, apart from the area of application.

Time: Immediate spreading after placing the blood sample is critical.
Angle: The angle of the spreader slide influences the smear's thickness; greater angles result in thicker, shorter smears.
Blood drop size: A proper blood drop size is essential for uniform spreading.
Speed: Rapid, even motion is required when spreading the blood.
Hematologic factors: If hematocrit is high, use a smaller angle; if it's low, use a larger angle during spreading.

Poor smear: Causes include blood drop too large or too small; jerky spreader motion; failure to keep the spreader and slide in contact; incorrect angle; failure to fully spread the blood; dirty or chipped slides;
Contamination: (slides contaminated with fat, grease, or water-contaminated methanol).
Biological factors:
- Cold Agglutinins: RBCs clump together; warm the blood before remaking smear.
- Lipemia: Holes appear in the smear; cannot be corrected.
- Rouleaux: RBCs stack like coins; cannot be corrected.

Drop of blood is too large or too small
Jerky spreader motion
Failure to keep spreader edge against slide
Failure to keep spreader at a 30° angle
Failure to fully push the spreader across
Irregular spread (ridges, long tails)
Dirty or chipped slide
Dusty slide
Holes in the smear
Cellular changes due to delay in fixing, inadequate fixation time, or methanol contaminated with water.