Blood film

A blood smear (blood film):

is a glass microscope slide coated on one side with a thin layer of venous blood. The slide is stained with a dye, usually Wright’s stain or leishman stain and examined under a microscope .

Aim of blood smear

Examination of thin blood films is important in the following states:-

investigation of anaemia, assessment of RBC and platelets morphology

Identification of parasites ,infections and other conditions which produce changes in the appearance of blood cells

differential count of leukocytes.

A blood film report can provide rapidly , low cost and useful information about a patient’s condition.

Making blood films

Three basic steps to make blood film:

1. Preparation of blood smear.

2. Fixation of blood smear.

3. Staining of blood smear.

BLOOD SMEAR

• Specimen:Peripheral blood smear made from

EDTA-anticoagulated blood. Smears should be made within 1 hour of blood

collection from EDTA specimens stored at room temperature to avoid alteration of cell morphology

Blood smears can also be made from finger stick blood directly onto slide.

• Equipment• Clean slides• Blood capillary tube or micropipette 10 µL

• EDTA tubes • Lancets and syringes .• Cotton and alcohol (disinfectant)• Leishman stain• Normal saline

Procedure:

1. Fill a capillary tube three-quarter full with the anticoagulated specimen.

2. Place a drop of blood, about 2 mm in diameter approximately an inch from the frosted area of the slide.

3. Place the slide on a flat surface, and hold the narrow side of the non frosted edge between your left thumb and forefinger.

4. With your right hand, place the smooth clean edge of a second (spreader) slide on the specimen slide, just in front of the blood drop.

5. Hold the spreader slide at a 30° angle, and draw it back against the drop of blood.

Procedure:

6. Allow the blood to spread almost to the edges of the slide.

7. Push the spread forward with one light, smooth, and fluid motion. A thin film of blood in the shape of a bullet with a feathered edge will remain on the slide.

8. Label the frosted edge with patient name, ID# and date.

9. Allow the blood film to air-dry completely before staining. (Do not blow to dry. The moisture from your breath will cause RBC artifact.)

Steps for Blood Film

The shape of blood film

Collection of Blood

5.Touch the drop of blood to the slide from below.

4.Slide must always be grasped by its edges.

2.Puncture at the side of the ball of the finger.

3.Gently squeeze toward the puncture site.

1.The second or third finger is usually selected and cleaned.

Preparing thin films

1.Touch one drop of blood to a clean slide.

.

. 4Wait to dry before fixing and staining.

3Pull the drop of blood across the first slide in one motion.

2-hold the spreader at 30degree angle.

The thickness of the spread when pulling

Is determined by:1. The angle of the spreader slide.

(the greater the angle, the thicker and shorter the smear).

2. Size of the blood drop.3. Speed of spreading

 Leishman's stain

  1-   Air dry slides .  2-   Flood with Leishman's stain for three minutes. 3-  Dilute the stain on the slide with an equal amount of

buffered water, pH 6.8, adding the water slowly with a plastic Pasteur pipette and mixing by sucking the stain up and down with the pipette.

 4-  Leave the slide for approximately 7-10 minutes. 5-  Wash off excess stain with slowly-running tap water.6- flood slide for one minute with buffered water, pH ( 6.8).7- Dry the slide . 

Characteristics of A Good Smear:

1. Surface : even and uniform , free from ridges ,waves and holes.

2. Length : About 2.5 cm long , the blood smear should occupy the central portion of the slide.

3. Margin: The blood smear should not touch the edges

4. Film consist of three parts: head , body and tail .

5. Tail end :will be gradually thin ,without any serrated ends .

The shape of blood film

 Sources of error

Irregular spread with ridges and long tail: Edge of spreader dirty or chipped; dusty slide

 Holes in film: Slide contaminated with fat or grease.

 Irregular leucocyte and platelet distribution, especially in tail: poor film-making technique

 Film too short and too thick: spreader held at incorrect angle

 Film extending to end of slide: blood drop too large  Short thin film: blood drop too small

 Film extends to edge of slide: spreader too wide or not positioned correctly

 Cellular degenerative changes: delay in fixing, inadequate fixing time or methanol contaminated with water

Examples of unacceptable smears