OSPE Station Name

Station 5 — Capillary Blood Sampling and Blood Smear

Learning Target
By the end of this station, the student should be able to:

1. Obtain capillary blood safely using the prick method from an appropriate sampling site.
2. Prepare a thin peripheral blood smear suitable for microscopic examination.

Required Material

• Disposable sterile lancet
• Cotton swabs
• 70% alcohol/spirit swab
• Clean glass slides
• Spreader slide
• Gloves
• Sharps disposal box
• Biohazard waste bin
• Microscope slide marker/pencil
• Leishman/Wright stain, if staining is required
• Microscope, if smear assessment is included

Student Task / Procedure

1. Wash hands and wear gloves.
2. Identify the correct capillary blood sampling site.
   • Adult: side of fingertip, usually ring or middle finger.
   • Infant: lateral or medial plantar surface of heel.
3. Clean the selected site with 70% alcohol and allow it to dry.
4. Hold the finger firmly and puncture the skin using a sterile disposable lancet.
5. Wipe away the first drop of blood with dry cotton.
6. Allow a fresh drop of blood to form without excessive squeezing.
7. Place a small drop of blood near one end of a clean glass slide.
8. Hold the spreader slide at about 30–45° angle in front of the blood drop.
9. Pull the spreader back to touch the blood drop and allow blood to spread along its edge.
10. Push the spreader smoothly and quickly forward to make a thin smear.
11. Allow the smear to air dry.
12. Dispose of the lancet immediately in the sharps container.
13. Apply cotton pressure to the puncture site.
14. Label the slide properly.

Observation / Identification Points

The student should demonstrate or identify:

• Correct site for capillary prick.
• Avoidance of central fingertip pulp and thumb.
• Proper cleaning and drying of the puncture site.
• Use of sterile disposable lancet.
• Wiping away the first blood drop.
• Avoidance of excessive squeezing of the finger.
• Correct size of blood drop.
• Correct spreader angle of 30–45°.
• Smooth, even, tongue-shaped blood smear.
• Thin feathered edge at the end of the smear.
• Proper disposal of sharps and contaminated material.

Result / Interpretation

A good peripheral blood smear should be thin, smooth, and tongue-shaped with a clear feathered edge. The cells should be evenly distributed, especially near the feathered edge, where red blood cells lie mostly in a single layer.

Principle:
A small drop of capillary blood is spread mechanically over a glass slide to create a thin film. This allows microscopic examination of blood cells, including red blood cells, white blood cells, and platelets.

Clinical Significance:
A properly prepared blood smear is useful for studying blood cell morphology, differential leukocyte count, anemia, infections such as malaria, platelet abnormalities, and other hematological disorders.

Common Student Mistakes

1. Pricking the wrong site or pricking the central pulp of the finger.
2. Not allowing alcohol to dry before puncture.
3. Using the first drop of blood for smear preparation.
4. Excessive squeezing of the finger, causing tissue fluid dilution.
5. Using too large or too small a blood drop.
6. Holding the spreader slide at an incorrect angle.
7. Making a thick, irregular, short, or long smear.
8. Not producing a feathered edge.
9. Touching the smear before drying.
10. Improper disposal of lancet or contaminated material.

AIM Feedback

A good capillary blood smear depends on three things: correct prick technique, correct blood drop size, and smooth spreading. Always choose a safe puncture site, wipe away the first drop, and avoid squeezing the finger too much. The smear should be thin with a feathered edge because this is the area where blood cells are best seen under the microscope. Poor technique can produce a thick or patchy smear, making cell identification difficult.

Most Important Viva Questions for This Topic

1. What is capillary blood sampling?
   Capillary blood sampling is the collection of blood from small superficial blood vessels by skin puncture.
2. Which finger is commonly used for capillary blood sampling in adults?
   The ring finger or middle finger is commonly used.
3. Which site is used for capillary blood sampling in infants?
   The lateral or medial plantar surface of the heel is used.
4. Why should the central pulp of the fingertip be avoided?
   It is more painful and may cause deeper tissue injury.
5. Why is the first drop of blood wiped away?
   It may contain tissue fluid and alcohol contamination, which can dilute or alter the sample.
6. Why should excessive squeezing of the finger be avoided?
   It causes tissue fluid to mix with blood, leading to dilution and inaccurate results.
7. What is the ideal angle of the spreader slide?
   Approximately 30–45°.
8. What are the features of a good blood smear?
   It should be thin, smooth, tongue-shaped, and have a feathered edge.
9. What is the feathered edge of a blood smear?
   It is the thin terminal part of the smear where cells are spread in a single layer.
10. Why is the feathered edge important?
    It is the best area for microscopic examination of blood cells.
11. Name two common stains used for peripheral blood smear.
    Leishman stain and Wright stain.
12. What is the clinical importance of a blood smear?
    It helps assess blood cell morphology, differential leukocyte count, anemia, platelet abnormalities, and blood parasites such as malaria.