What type of leukemia is characterized by an excess of immature white blood cells?

The type of leukemia characterized by an excess of immature white blood cells is Acute Lymphoblastic Leukemia (ALL). In ALL, there is a rapid proliferation of lymphoid precursor cells which are not fully developed, leading to a high number of these immature cells in the bloodstream and bone marrow. This condition often affects children but can also occur in adults.

The defining feature of ALL is the rapid accumulation of these immature lymphoblasts, which impairs the body's ability to produce normal blood cells, resulting in symptoms like fatigue, increased infections, and bleeding. The nature of the disease being acute indicates that it progresses quickly, in contrast to more chronic forms of leukemia where the cells involved may mature more slowly and symptoms may develop over a longer period.

In contrast, Chronic Lymphocytic Leukemia (CLL) and Chronic Myeloid Leukemia (CML) involve more mature forms of lymphocytes or myeloid cells that accumulate over time, rather than immature cells. Acute Myeloid Leukemia (AML) also involves immature cells, but these are typically of myeloid lineage rather than lymphoid. Therefore, the distinguishing factor for Acute Lymphoblastic Leukemia is its specific characteristic of having an excess of immature lymphoid cells