Elevated serum creatinine level in thyroid cancer patients undergoing withdrawal of throxine therapy for radioiodine scan/treatment

ABSTRACT

Chronic hypothyroidism is known to cause a significant reversible decrease in glomerular filtration rate [GFR], However, the effect on GFR of acute hypothyroidism, routinely induced in thyroid cancer patients in preparation for radioiodine scan/treatment, is not known. We studied the prevalence of abnormal serum creatinine level and the degree of its increase in hypothyroid patients with thyroid cancer four weeks after the withdrawal of thyroxine therapy. Creatinine level was measured in 116 patients on 191 hypothyroid episodes and in 56/116 and 18/116 patients while euthyroid or mildly hyperthyroid respectively. Abnormal creatinine level was significantly more prevalent in the hypothyroid state [34.5% vs 4% in the euthyroid or mildly hyperthyroid states] and significantly more common in males [50% vs 29% in females], in patients patients] and in patients with a TSH level >150 mU/L [55% vs 30% with TSH females only or including all hypothyroid episodes did not significantly alter the results. Further, compared to patients with normal creatinine level, patients with abnormal creatinine levels were significantly younger [in the whole group. mean age 35.1 vs 42.5 years; in the subgroup of patients with a TSH level > 150 mU/L, 29.8 vs 41.4 years; in females, 28.3 vs 42.5 years] and there was a significant negative association between the presence of abnormal creatinine levels and different age groups. Compared to levels obtained in the euthyroid or mild hyperthyroid states, creatinine levels increased in the hypothyroid state on average 32% [23micro M/L, P=0.0001] with 24% of patients having >/= 50% increase. Elevated serum creatinine levels are rather common in thyroid cancer patienis undergoing temporary withdrawal of thyroxine treatment and more so in males, younger patients or in association with higher TSH levels. Since the clearance of iodine is linearly related to GFR, our study suggests that in the setting of hypothyroidism, the bioavailability of a given dose of radioiodine may have significant individual variation