Blood Smear Preparation and Evaluation Notes

Blood Smear Preparation and Evaluation

• Purpose of Blood Smears

  • Estimate white blood cell (WBC) count and perform differential counts, RBC and platelet morphology and estimation, identify blood parasites.

• Preparation Methods

  • Wedge Technique: Most commonly used, produces a flame/thumb-shaped smear with a large monolayer (one cell layer thick).

  • Coverslip Technique: Primarily for exotics.

  • Smears should be made as soon as possible after sample collection.

• Wedge Technique Essentials

  • Use clean, dry slides; use fresh whole blood or well-mixed ethylenediaminetetraacetic acid (EDTA) blood.

  • Label slide on frosted edge. Prepare with a spreader slide held at a $30^\circ$ to $45^\circ$ angle; higher angle shortens the smear.

  • Pull spreader into blood drop, then push forward swiftly, steadily, and straight, without lifting.

  • Rapid air drying prevents artifacts.

• Common Problems and Causes

  • Artifacts: Slow drying.

  • Thin Smear: Spreader angle <30^\circ, too fast spread, anemia. Leads to crushed/distorted cells.

  • Thick Smear: Spreader angle >45^\circ, too much blood, hemoconcentration. Results in small/dark WBCs, overlapping cells, thin monolayer.

  • Slow Push: Segmented WBCs/monocytes concentrated at feathered edge, cell distortion.

• Staining the Slide

  • Performed on a completely dry smear to differentiate WBC types and detect abnormalities.

  • Romanowsky stains (e.g., Wright's, Giemsa, Modified Wright's) are common.

  • Always rinse with distilled water as the last step and ensure the slide is completely dry before microscopic evaluation.

  • Grossly evaluate the smear first for size, shape, monolayer quality, and absence of air bubbles, streaks, or stain precipitate.

• Staining Problems

  • Over-staining, over-rinsing, improper smear drying.

  • Using old/dirty stain; always empty, clean, and refill jars instead of adding more stain.

  • Water contamination of the fixative solution.