Blood Smear Quality: Critical Factors for Accurate Microscopy

Pre-Analytical Variables

1. Sample freshness: Collect in EDTA; prepare smears within 2 hours to avoid morphological artifacts.
2. Anticoagulant adequacy: No clots; clots indicate insufficient mixing or excess blood.

Slide Preparation

1. Clean slides: Grease-free, lint-free; use alcohol wipe if needed.
2. Drop size & angle: Small drop, 30–45° spreader angle for monolayer.
3. Film thickness: Feathered edge should be one cell thick; no thick “body”.

Staining

• Romanowsky-type (Wright-Giemsa, May-Grünwald-Giemsa) – proper pH buffer (6.8–7.2), stain time, rinse.
• Automated stainers improve consistency.

Microscopy

• 100× oil immersion for differential; 40×/50× for scan.
• Systematic scanning: avoid feathered edge, thick area; evaluate 100–200 WBCs.
• Check for artifacts: smudge cells, water holes, stain precipitate.

Quality Assurance

Daily stain QC, periodic slide review, proficiency testing ensure reliable results.