Blood Smear Preparation Guide

Blood Smear Preparation

• 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.

Procedure

• 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.

Characteristics of a Good Smear

• 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.

Factors Affecting Smear Quality

• 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.

Issues with Smears

• 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.

Common Causes of Poor Quality Smears (List)

• 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.