Radioactive iodine (RAI) therapy is used to treat patients with differentiated thyroid cancer (DTC), in which radioactive iodine (131I) is administered in doses of 27–54 mCi in low-dose ablation followed by measurements of thyroglobulin levels. The present study aimed to determine the suitability of 99mTc scintigraphy for detecting the rate of successful ablation of thyroid remnants after low-dose administration. The study included 500 patients with DTC. All participants underwent total thyroidectomy during the time period between 2015–2019 and they were all given radioactive iodine at 27–54 mCi. All participants underwent thyroid scan using measurements of 99mTc-perticinate and thyroglobulin level prior to treatment. Both tests were repeated 6 months later. Post administration of the 131I ablation dose, whole-body scans (WBS) were performed and comparisons between the pre- and post-ablation dose. The results showed that the use of 99mTc-pertechnetate showed 117 of 229 cases (51.1%) with thyroid remnants and 10 out of 53 cases (18.8%) with lymph node metastases. The average thyroglobulin (Tg) level for the remaining 112 patients out of 229 (48.9%), and for the 43 patients out of 53 (81.2%) was high, 4.21 and 3.3, respectively. Optimal cut-off values for Tg and 99mTc-pertechnetate uptake were at 0.8 ng/mL (sensitivity 66%, specificity 68%, area under curve, 0.63, P = 0.022) and 0.7% (sensitivity 72%, specificity 57; area under curve, 0.72; P = 0.024) respectively. In summary, 99mTc-perfechnetate scintigraphy is better than Tg level measurements in predicting successful ablation with low-activity RAI.