NHA Phlebotomy Certification Practice Exam

All of the following are formed elements found in the blood except:

1. Erythrocytes

2. Platelets

3. Macrophages

4. Leukocytes

The correct answer is: Macrophages

Formed elements in the blood refer specifically to the various cellular components that are suspended in plasma. These include erythrocytes, also known as red blood cells, which are responsible for oxygen transport; platelets, essential for blood clotting; and leukocytes, or white blood cells, which are integral to the immune response. Macrophages, however, are not considered formed elements of blood. They are a type of white blood cell but are primarily found in tissues rather than circulating in the bloodstream. When white blood cells are in circulation, they are typically referred to as leukocytes, encompassing various types, including neutrophils, lymphocytes, monocytes, and basophils. The distinction lies in the fact that while macrophages originate from monocytes (a type of leukocyte), and play crucial roles in the immune system by engulfing and destroying pathogens, they are not counted among the circulating elements of blood. Instead, they exist primarily as part of the body's tissue response to infection and inflammation, indicating their role in the immune system beyond the bloodstream.