Effect of hemodialysis on thyroid scintigraphy and thyroid uptake of iodine-131 and the role of scintigraphy on diagnosis of thyroid disease in chronic renal failure

Since the kidney plays an important role in the metabolism, degradation and excretion of several thyroid hormones, thyroid metabolism is affected in end stage renal failure (ESRF). A total of 32 patients with ESRF were included in this study. The thyroid scintigraphy with Tc-99m pertechnetate was performed in all hemodialysis patients before and after dialysis. The images at 15 and 50 minutes after injection were obtained and than uptake was calculated by software. After another dialysis session, I-131 uptake was achieved at 4 and 24-hours following the administration of I-131 orally. We found that there was not statistical difference between early and late uptake of Tc-99m pertechnetate both on before and after dialysis in the hemodialysis patients (p>0.05), but calculated uptake of late image was high. In CAPD group, the difference between early and late uptake was significant (p<0.05) and I-131 uptake at 24 hours was lower than hemodialysis subjects (p<0.01). The excessive uptake of Tc-99m pertechnetate by thyroid tissue in late scan may be due to reduction of functional activity of sodium-iodine symporter. The presence of low I-131 uptake in the CAPD patients compared to hemodialysis patients may be due to excessive iodine pool in these patient groups. Discordance between Tc-99m pertechnetate uptake and I-131 uptake by thyroid was higher than normal. Disharmony between ultrasonography and thyroid scintigraphy was determined in 21.4% of patients. In ESRF patients, who did not have any thyroidal complaint and have ultrasonographically homogenous thyroidal parenchyma, irregular radioactivity distribution on scintigraphy may cause misleading results.