What is the Difference Between Thin and Thick Smear

The key difference between thin and thick smear is that thin smear is a type of blood smear where a drop of blood is spread across a large area of a slide, while thick smear is a type of blood smear where a drop of blood is kept on a glass slide.

A blood smear is a thin layer of blood smeared on a glass slide. It is stained in such a way as to allow the various blood cells to be observed under the microscope. Blood smears are routinely used to detect blood disorders and to identify blood parasites such as those of malaria and filariasis. Thin and thick smears are two different types of blood smears.

CONTENTS

1. Overview and Key Difference
2. What is Thin Smear 
3. What is Thick Smear
4. Similarities – Thin and Thick Smear
5. Thin vs Thick Smear in Tabular Form
6. Summary – Thin vs Thick Smear

What is a Thin Smear?

A thin smear is a type of blood smear where a drop of blood is spread across a large area of a slide. Thin blood smears help to discover which species of parasite is causing the infection. Moreover, a thin smear consists of blood spread in a layer in such a way that the thickness decreases gradually toward the feathered edge. In the feathered edge, the cells are in a monolayer, not touching one another. A thin smear is usually similar to a blood film, and it allows species identification. This is because the appearance of parasites is best preserved in this type of blood smear preparation. However, it is less sensitive than a thick smear.

Thin smears can be made by placing a small drop of blood on a pre-cleaned slide near its frosted end, bringing another slide at a 30-45° angle up to the drop, allowing the blood drop to spread along the contact line of the two slides, and quickly pushing the upper slide toward the unfrosted end of the lower slide. Furthermore, the thin smear should be fixed by dipping in absolute methanol before usage.

What is a Thick Smear?

A thick smear is a type of blood smear where a drop of blood is kept on a glass slide. Thick blood smears are most useful for detecting the presence of parasites. It allows microscopists to screen a larger blood volume, and it is about eleven times more sensitive than a thin smear. Therefore, picking up a low level of infections is easier on a thick smear. However, the appearance of the parasite is distorted in thick smears. Hence, distinguishing between different species can be very difficult.

Thick smears can be made by placing a small drop of blood in the center of the pre-cleaned slide, spreading the drop by using an applicator stick until its size reach approximately 1.5cm^2, and allowing it to dry.

What are the Similarities Between Thin and Thick Smear?

• Thin and thick smears are two different types of blood smears.
• Both smears contain red blood cells.
• They are used to detect blood disorders and to identify blood parasites.
• Both are used in a clinical laboratory setup.

What is the Difference Between Thin and Thick Smear?

A thin smear is a type of blood smear where a drop of blood is spread across a large area of a slide, while a thick smear is a type of blood smear where a drop of blood is kept on a glass slide. Thus, this is the key difference between thin and thick smear. Furthermore, a thin smear is less sensitive than a thick smear.

The below infographic presents the differences between thin and thick smear in tabular form for side by side comparison.

Summary – Thin vs Thick Smear

Thin and thick smears are two different types of blood smears that contain red blood cells. In a thin smear, a drop of blood is spread across a large area of a slide. In a thick smear, a drop of blood is put on a glass slide. So, this is the key difference between thin and thick smear.

Reference:

1. “Staining Thick and Thin Blood Smears.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention.
2. “CDC – DPDX – Diagnostic Procedures – Blood Specimens.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention.

Image Courtesy:

1. “Good, examples, appearance, thick, thin, blood smears, examined, microscope” (CC0) via Pixino
2. “Prepared, slide, offers, example, appearance, satisfactory, thick, film, blood smear” (CC0) via Pixino