AAB Medical Technologist (MT) 2026 – 400 Free Practice Questions to Pass the Generalist Exam

The essential marker for distinguishing acute lymphocytic leukemia (ALL) from malignant lymphoma is terminal deoxynucleotidyl transferase (TdT). TdT is a DNA polymerase that is typically expressed in immature lymphoid cells, particularly in precursor B and T lymphoblasts. Its presence is a hallmark of acute lymphoblastic leukemia and helps in classifying the disease.

In the context of differentiation between ALL and lymphomas, TdT positivity indicates a more immature, leukemic stage of lymphocyte development, which is characteristic of ALL. In contrast, malignant lymphomas usually consist of more mature lymphoid cells and typically do not express TdT. Therefore, when a cell population is analyzed for TdT, a positive result suggests that it is likely indicative of acute lymphocytic leukemia rather than a malignant lymphoma. This makes TdT a key diagnostic marker in hematopathology for differentiating these two conditions.

Other markers such as CD34, CD20, and CD19 can indicate various stages of lymphocyte maturation and are often present in both ALL and certain types of lymphomas, thereby making them less specific for distinction between these two diseases.