Haematological effects from radioiodine treatment of thyroid carcinoma

The changes in peripheral blood counts and number of colony forming cells (CFU-c) in the bone marrow after 131I treatment for thyroid cancer were followed in 24 patients. The median WBC declined to 78% and the median blood platelet count to 69% of the pretreatment values after 4 treatments. In 4 patients a moderate pancytopenia developed and in 1 patient additionally treated with chemotherapy and preleukaemia was suspected. In 19 bone marrow samples obtained from 13 patients no difference in number of CFU-c could be found related to cumulated 131I activities given to those patients. In 5 of 7 patients examined between the 9th and the 19th day afer a treatment the number of CFU-c had declined by 50% or more. It is concluded that radioiodine exerts a protracted suppressive effect on the bone marrow which is seldom severe. Agar culture of bone marrow cells with counting of CFU-c was not found to be more sensitive than the peripheral blood counts in predicting bone marrow damage and cannot be recommended for routine use.