Effects due radioiodine therapy for thyroid cancer in renal glomerular filtration rate: randomized study comparing thyroid hormone withdrawal with the use of recombinant human thyroid stimulating hormone (rhTSH)

Glomerular filtration rate (GFR) was studied in well differentiated thyroid cancer patients referred for radioiodine therapy (RIT). The study evaluated GFR during thyroid stimulating hormone (TSH) stimulation after thyroid hormone withdrawal (THW) or after recombinant human thyroid stimulating hormone (rhTSH), correlated GFR with thyroid hormone profile, evaluated GFR during and in the week after RIT, evaluated GFR and whole body radiation effective dose, and correlated different methods for GFR determination. 28 patients were included in a non-blinded randomized clinical trial and divided in two groups of 14 patients, being group A (GA) stimulated by THW and group B (GB) stimulated by rhTSH. Patients had GFR determined by ⁵¹Cr-EDTA, as well as serum thyroid hormone profile, creatinine, albumin and urea before and after TSH stimulation, and after RIT had determined their serum creatinine, albumin and urea and whole body radiation effective dose. Creatinine, albumin and urea were used to estimate GFR by serum creatinine, Modified Diet in Renal Disease (MDRD), and Cockcroft-Gault equations. GA presented a -18,5% GFR variation by 51Cr-EDTA varying from 94,4±18,6 mL/min before THW to 76,2±15,7 mL/min after THW (p=0,0002) while GB presented a 4% GFR variation by 51Cr-EDTA varying from 90,8±18,4 mL/min before TSHrh to 92,6±15,2 mL/min after rhTSH (p=0,64). GFR significantly varied only in GA without presenting proportionality with thyroid hormone variation. There was no correlation between rise in TSH levels and GFR. Creatinine equations demonstrated a sustained reduction in GFR during THW and GFR stability after thyroid hormone reposition, while GB presented stable GFR during the whole study. Whole body radiation effective dose did not present significant differences between the two groups (p=0,76). Comparing 51Cr-EDTA and GFR estimative equations presented Pearson correlation score of 0,78 for serum creatinine, 0,79 for MDRD and 0,66 for Cockcroft-Gault, while comparison between variances in GA between 51Cr-EDTA e serum creatinine equation was significantly different. In conclusion GFR presents a reduction during THW related to hypothyroidism and not to TSH rise and stabilizing after thyroid hormone therapy, GFR does not vary during rhTSH, whole body radiation effective dose does not vary between the two groups proportionally to GFR, and that MDRD equation had the best correlation with 51Cr-EDTA. (author)