Blood Smear Preparation Methods

Blood Smear Preparation

• Blood smears are mounted with DPX mountant, film side down on glass slides.

Advantages of Cover Slip Method

• WBC and platelets are more evenly distributed
• More of the prepared film can be examined
• Decreases sampling error
• Used for bone marrow aspiration smear

Advantages of Slide Method

• Slides are not easily broken
• Slides are easier to label and stain
• Easier to handle large numbers of films
• Easier to learn the technique
• RBCs are well distributed

Preparation of Thick Blood Film

• Thick blood smears are used for diagnosis of blood parasites, particularly malaria
• Gives higher percentage of positive diagnosis in less time (10 times thicker than normal smears)
• Procedure: place a small drop of blood on a clean slide, spread with an applicator stick until small prints are just visible

Other Types of Smears

• Automated spun smear
• Buffy coat smear
• Prepared from buffy coat layer (WBC and platelets)
• Valuable in leucopenia and diagnosis of malaria and visceral leishmaniasis

Characteristics of an Acceptable Smear

• Free of visible clotting
• Not too thick or too thin
• Gradual transition to thickness
• Smooth 'tail'
• Feathered edge
• Origin of blood drop is at the center of the smear
• Smooth, homogeneous, and no clots, holes, or bubbles

Sources of Error in Making a Smear

• Size of blood drop:
  • Too much blood makes the blood film thicker
  • Too low an angle and the smear is too long
  • Too high an angle and the smear is too short
• Speed
• Too much pressure on the push slide
• Dirty slides
• Delay in spreading blood drop
• Failure to completely spread blood drop
• Stopping abruptly before completely spreading the blood drop
• Pushing the spreader slide too quickly or too slowly

Technical Tips

• Mix EDTA anticoagulated blood properly before making the smear
• Use capillary tubes to deliver the original drop of blood
• Angle of push may need to be adjusted depending on blood viscosity
• Slides must be clean, not damaged, with no chips or cracks
• A feather edge or bullet-shaped appearance indicates a good smear
• Faster spreading makes the film thicker and shorter
• Bigger angle of spreading makes the film thicker
• Caution: clumping of platelets if the drop sits for longer than 3-5 seconds before spreading

Quiz on the different methods of blood smear preparation, including the cover slip and slide methods, and their advantages. Learn about the best practices for mounting and examining blood smears.