The thymus is the primary site of terminal deoxynucleotidyl transferase (TDT)–positive cells, and TDT is found in the nucleus of the more primitive T cells. A thymus-related population of TDT-positive cells resides in the bone marrow (normally a minor population, 0%–2%). TDT is increased in more than 90% of cases of ALL of childhood. A minor (5%–10%) population of patients with acute nonlymphoblastic leukemia have TDT-positive blasts. TDT-positive blasts are prominent in some cases of chronic myelogenous leukemia (CML), relating to the development of an acute blast phase. TDT has been reported to assist in establishing the diagnosis of ALL. TDT-positive cases of blast-phase CML correlate with a positive response to chemotherapy (vincristine and prednisone).
Obtain a 5-mL EDTA-anticoagulated peripheral blood sample or a 2-mL EDTA-anticoagulated bone marrow aspirate. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered.
Dry slides (store at room temperature for up to 5 days), process, and stain and then examine under the microscope for positive cells.
TDT is positive in ALL, lymphoblastic lymphoma, and CML (blast crisis).
TDT is negative in patients in remission and in those with CML or chronic lymphatic leukemia.
Pretest Patient Care
Explain test purposes and procedures.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.