What condition is defined by an insufficient number of platelets in the blood?

Thrombopenia refers to a condition where there is an insufficient number of platelets in the blood. Platelets are crucial for blood clotting; they help prevent excessive bleeding by aggregating at a site of injury and forming a plug. When the platelet count is low, which is the hallmark of thrombopenia, a person may experience increased bruising, prolonged bleeding from cuts, or spontaneous bleeding in severe cases.

The other options pertain to different medical conditions: leukemia is a type of cancer affecting blood and bone marrow, often leading to an overproduction of abnormal white blood cells; pancarditis refers to inflammation of the entire heart, which is unrelated to platelet counts; and obstruction generally describes a blockage in a part of the body, which does not connect to the concept of platelet deficiency. Understanding thrombopenia is important because it highlights the role of platelets in the hemostatic process and the potential complications that can arise from their deficiency.