Immunoperoxidase determination of terminal deoxynucleotidyl transferase in acute leukemia using PAP and ABC methods: experience in 102 cases.

Immunoperoxidase (IP) and immunofluorescence (IF) technics for the detection of terminal deoxynucleotidyl transferase (TdT) were applied to 102 cases of acute leukemia to compare their relative usefulness in the diagnosis and classification of acute leukemia. Two different IP technics were used, peroxidase-antiperoxidase (PAP) on 50 cases, avidin-biotin-peroxidase complex (ABC) on 42 cases, and both PAP and ABC on ten cases. Using 40% TdT+ cells to define positivity, 71 of 102 cases were IP+/IF+, 12 were IP+/IF-, and 19 were IP/IF-. The finding of 12 IP+/IF- cases suggests greater sensitivity of the IP method in detecting TdT+ acute leukemia. This greater sensitivity was demonstrated by both PAP and ABC technics. Direct comparison of ABC and PAP technics in ten cases showed the results by both methods to be similar. In addition, previous reports utilizing the IF method found approximately 10% of cases of AML to have greater than 10% TdT+ cells. The authors' findings for the IF method were similar (15%), but using the IP methods, the authors were able to detect greater than 10% TdT+ cells in 46% of AML cases and greater than 40% TdT+ cells in 31% of AML cases. The authors conclude that the IP technics for the detection of TdT offer several advantages and may be more sensitive relative to the IF method. Further, either the PAP or the ABC method is suitable for routine use in hematopathology laboratories.