Terminal deoxynucleotidyl transferase activity in acute leukemia: A study of 100 cases comparing an immunoperoxidase (PAP) vs immunofluorescent method

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Abstract
A comparison between the immunofluorescent (IF) method for terminal deoxynucleotidyl transferase (TdT) activity and the immunoperoxidase (IP) method by peroxidase‐anti‐peroxidase (PAP) technique was done for 100 cases of acute leukemia. For the acute lymphoblastic leukemias (ALL) there was agreement in 93% of the cases. However, the IP method detected 51/55 (93%) TdT+ cases versus 47/55 (85%) by the IF method. For the acute nonlymphocytic leukemias (ANLL), there was an agreement in 89% of the cases. The IP method detected 8/36 (22%) TdT‐positive cases while IF detected 4/36 (11%) positive cases. If a figure of 10% TdT+ cells is considered significant in the marrow of the ANLLs, then the IP method would detect eight additional cases for a total of 16/36 (44%) TdT+ cases. This latter figure questions the ability of the IP TdT assay as a single test adequately to determine the lineage of a cell line. It may be rather that TdT is a marker that is expressed in a stem cell.