What condition is characterized by low levels of platelets in the blood?

Thrombocytopenia is specifically defined as a condition where there are low levels of platelets in the blood. Platelets, or thrombocytes, are crucial for blood clotting and wound healing. When their numbers are decreased, the body's ability to form clots effectively is impaired, leading to an increased risk of bleeding and bruising.

In contrast, anemia refers to a deficiency of red blood cells or hemoglobin, which affects oxygen transport but does not directly pertain to platelet levels. Leukemia is a type of cancer that affects blood cells, particularly white blood cells, and can lead to other hematological abnormalities, including issues with platelets, but it does not specifically describe low platelet counts. Hemophilia is a genetic disorder that affects the blood's ability to clot due to deficiencies in clotting factors, rather than a direct reduction in platelet count.

Therefore, the defining characteristic of thrombocytopenia as a condition is its association with low platelet levels.