Mild decreases in white blood cell and platelet counts are present one year after radioactive iodine remnant ablation.

BACKGROUND Bone marrow suppression after multiple, high-dose radioactive iodine (RAI) therapies is well described. However, changes in the peripheral complete blood count (CBC) that may occur after a single treatment of RAI such as that commonly used for routine remnant ablation is much less well studied. In this retrospective trial, we examined the rate of persistent anemia, leukopenia, and thrombocytopenia 1 year after a single RAI administration. METHODS Peripheral blood counts at baseline were compared to those obtained 1 year after RAI remnant ablation in 206 consecutive thyroid cancer patients. Analyses were performed to determine the potential impact of both the method of preparation (recombinant human thyroid stimulating hormone [rhTSH] vs. thyroid hormone withdrawal) and administered activity of (131)I on hemoglobin, white blood cell (WBC), and platelet counts. RESULTS Comparison of the baseline CBC before RAI ablation (median administered activity of approximately 3700 MBq or 100 mCi) with the follow-up CBC done 1 year later demonstrated a statistically significant decline in total WBC (6.7 +/- 2.1 x 10(9) vs. 6.0 +/- 1.8 x 10(9)/L, p < 0.001; 9.7% below the reference range at 1-year follow-up) and platelet (272 +/- 67 vs. 250 +/- 65 x 10(9)/L, p < 0.001; 5.8% below the reference range at 1-year follow-up) with no significant change in hemoglobin (1.40 +/- 0.14 vs. 1.40 +/- 0.14 g/L or 14.0 +/- 1.4 vs. 14.0 +/- 1.4 g/dL; 1.5% below the reference range at 1-year follow-up). There were no significant clinical complications observed during the 1-year follow-up period. The changes in total WBC and platelets were not related to the method of preparation or the administered activity of RAI. CONCLUSION A single RAI treatment of approximately 3700 MBq (100 mCi) after thyroidectomy is associated with a statistically significant, mild decline in WBC and platelet counts that persists for at least 1 year after ablation. Given the small magnitude of the changes and the lack of clinically significant adverse events, these observations should not decrease the use of RAI ablation in moderate to high-risk patients in whom the benefits of ablation are likely to outweigh these minor risks.