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

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.