The Correlation Study Between TgAb And ¹⁸F-FDG PET/CT Results In Differentiated Thyroid Cancer Patients

Objective:To evaluate the relationship between TgAb and its derivatives and positive ¹⁸F-FDG PET/CT in patients with elevated thyroglobulin antibody（TgAb）after surgery for differen-tiated thyroid cancer（DTC）,and the diagnostic efficacy.Methods:This retrospective study included 177 patients with DTC who received ¹⁸F-FDG PET/CT examination and were serum TgAb-positive at the Department of Nuclear Medicine of Shanxi Bethune Hospital from March 2019 to August2022.Firstly,patients were divided into positive group（B1 group）and negative group（B2group）according to the results of ¹⁸F-FDG PET/CT examination,to compare whether there were differences in TgAb level,TgAb×Tg product and clinical features between the two groups.The product of TgAb and TgAb×Tg was calculated by receiver operating character-istic curve（ROC）to evaluate the optimal critical value and diagnostic efficiency for predict-ing ¹⁸F-FDG PET/CT results.Secondly,patients who had received two or more TgAb tests（74 cases）were again divided into ¹⁸F-FDG PET/CT positive group（D1 group）and negative group（D2 group）.The difference of TgAb doubling time（DT）between the two groups was analyzed,and ROC analysis was used to evaluate the optimal threshold value and diagnostic efficiency for predicting ¹⁸F-FDG PET/CT results.Results:The levels of Tg×TgAb in group B1 were higher than those in group B2,with statistical significance（Z=2.20,P=0.028;Z=-3.85,P=0.001）.However,the TgAb of group B1 and B2was not statistically significant（P>0.05）.B1 than B2 group have more patients with distant metastasis（?²=8.55,P=0.003）.Other T stages,N stages,risk stratification,and tumor pathological features（Hashimoto’s thyroiditis,whether it is multifocal,lesion location,cap-sule invasion,pathological type and lesion size）were not statistically significant（P<0.05）.The product of Tg×TgAb predicted the specificity and sensitivity of ¹⁸F-FDG PET/CT results to be 61%and 69%,and the product AUC under the curve was0.678（0.591-0.766,P<0.001）,with an optimal critical value of 73.41.Secondly,in D1 and D2 groups,The DT of group D1 is higher than that of group D2（Z=-0.00,P=0.004）.ROC curve analysis showed that the specificity and sensitivity of DT to predict the results of ¹⁸F-FDG PET/CT examination were were 77%and 74%,AUC=0.704（0.5770.830,P=0.004）,and the optimal critical value was-51.68 days.Conclusion:1.For patients with elevated TgAb after surgery,the premise is that the detection method needs to use Roche electrochemiluminescence method.For patients whose T g Ab×Tg product is higher than 73.41,¹⁸F-FDG PET/CT examination is recommende d.2.Patients with TgAb doubling time higher than-51.68 days are also recommended to undergo ¹⁸F-FDG PET/CT examination,which is conducive to the decision of t he next treatment plan for patients.3.The relationship between TgAb and ¹⁸F-FDG PET/CT results remains uncertain.