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Peripheral Blood Smear

A blood smear, also known as a peripheral blood smear or blood film, is a widely used diagnostic laboratory technique used to examine the shape, size, and frequency of the blood components under a microscope. This technique can provide valuable information about the health of a patient and can contribute to the diagnosis of blood-related pathologies such as anemias, leukemias, clotting disorders, and infections.

Making a blood smear (see Figure 1):

  1. A droplet of blood is taken directly from a patient (using a finger prick) or from a fresh blood sample and added to one end of a clean microscope slide.

  2. Holding a second, clean microscope slide (called the spreader slide) at a 45° forty five degree angle, put the short edge of the slide in front of the blood droplet so that the blood ‘latches’ onto the spreader slide.

  3. Quickly and smoothly push the spreader slide along the length of the base slide spreading out the blood droplet as you go.

  4. The final blood smear should look like a film of blood spread over the slide with a thin ‘feathered edge’ at one end. The cells in the thinnest part of the blood smear will be spread out in a single layer, enabling accurate viewing of the blood components under the microscope.

After the blood smear has been completed it needs to be fixed to preserve the cells in their natural state and avoid artifacts forming:

  1. Leave the blood smear to air dry naturally.

  2. The blood smear can then be further fixed using a chemical fixative such as methanol.

  3. The blood smear will need to thoroughly air dry once again after chemical fixation.

To visualize the blood components the blood smear will need to be stained by one of several common techniques depending on the analysis required and time for the analysis.

This image illustrates the step-by-step process for preparing a peripheral blood smear using the two-slide method. The process starts with a small drop of blood, labeled as less than 10 micro liters placed near one end of a clean glass slide, which is called the base slide The first diagram shows a gloved hand holding a second slide, called the spreader slide This spreader slide is brought into contact with the base slide, just in front of the blood drop. The spreader slide is held at an angle of 30 to 45 degrees relative to the base slide. In the second diagram, the spreader slide is pulled back until its edge touches the drop of blood The blood quickly spreads by capillary action along the entire width of the spreader's edge. In the third diagram, the spreader slide is then smoothly and rapidly pushed forward along the base slide. This motion drags the blood drop behind it, creating a uniform, thin film of blood.

Figure 1. Steps to create a peripheral blood smear.

Referred from:

Article
Giemsa staining
Article
Malaria
Article
Sickle Cell Disease