Terminal deoxynucleotidyl transferase immunofluorescence of bone marrow smears: experience in 156 cases.

Terminal deoxynucleotidyl transferase (TdT) is a valuable marker for non-B-, non-T-, and T-cell lymphoblastic disorders. Determination of TdT activity by enzymatic assay is laborious and requires fresh cells. The authors evaluated a new technic for TdT determination, using indirect immunofluorescence on air-dried bone marrow smears. Specimens from 156 consecutive patients with hematologic, oncologic, and other disease states were tested. The TdT visualization by indirect immunofluorescence gives results comparable to those previously reported for lymphoproliferative disorders. Several unusual cases with positive TdT were uncovered. TdT by indirect immunofluorescence is a convenient and rapid technic that enables easier access to TdT determinations than the enzymatic assay.