Background: We hypothesized that postoperative lymph node status would affect I-131
uptake (RIU) due to pathophysiological behavior of benign and malign thyroidal tissue. This retrospective
study was designed to assess whether RIU would predict the presence of lymph node metastasis
Methods: Data for differentiated thyroid cancer patients who received postoperative I-131 therapy
at our institution between 2013 and 2016 were reviewed. Age, histopathology, TSH, Tg, anti-Tg, 2
and 24 hour RIU (2-24RIU), ultrasonography, I-131 dose, scans were reviewed. Patients were divided
into groups according to lymph node status. The ΔRIU was calculated (ΔRIU=24RIU-2RIU)
to define different metabolic behavior of I-131. Patients were grouped according to ΔRIU to assess
the sensitivity, specificity, negative/positive predictive values, accuracy of ΔRIU predicting LNM.
Results: 198 patients (38 males /160 females, age: 47±14 years) who received mean: 118±27 mCi I-
131 were enrolled in the study. There was no difference between ages, TSH level, 2RIU values and
the I-131 therapy dose of patients with and without LNM. Tg, anti-Tg, 24RIU, ΔRIU values were
higher in patients with LNM. Patients with ΔRIU≥1% had higher Tg values (mean±std:
16.63±46.53 vs. 6.70±31.18, p: 0.04). When ΔRIU≥1% was used for predicting LNM, sensitivity,
specificity, positive, negative predictive values, diagnostic accuracy were, 66%, 72%, 64%, 74 %,
and 70% respectively.
Conclusion: RIU was evaluated to predict neck LN status in this study. The sensitivity and specificity
were comparable with modalities which are commonly used for determination of LNM. In light
of the results of this study, when a pre-therapy RIU increase in time is observed, carrying out further
investigation protocols for LNM, would contribute to pre-therapy staging.