The Diagnostic Value Of Serum TgAb Value And Its Changes On The Prognosis Of DTC Patients With Positive TgAb

Differentiated thyroid carcinoma?DTC?is one of the most common pathological types of thyroid cancer.It has become the fastest growing incidence of cancer in recent years.Currently,most DTC patients can achieve long-term survival under the comprehensive treatment with thyroid surgery as the main method,¹³¹I treatment and TSH inhibition as the auxiliary method.However,a small proportion of DTC patients have recurrence/metastasis during follow-up.So it is great importance for DTC patients to go for long-term follow-up after treatment.The detection of serum thyroglobulin?Tg?,cervical ultrasound?US?examination and diagnostic radioiodine¹³¹I diagnostic whole body scan(¹³¹I-Dx-WBS)were the main contents of post-treatment follow-up of DTC patients at present.Tg is a large molecule glycoprotein synthesized by thyroid follicular epithelial cells,which only comes from normal thyroid tissues and DTC lesions.Serum Tg should theoretically be undetectable or at a very low level after thyroid surgery and¹³¹I ablation treatment for patient with DTC.If the level of Tg is elevated,it indicates the existence of thyroid tissues or DTC metastases that secreting Tg in the patients.Therefore,Tg is often used as a tumor marker in the follow-up of patients with DTC after thyroid surgery.However,the Tg electrochemiluminescene immunoassay results will lower than the actual value in the presence of Thyroglobulin antibody?TgAb?,so as to conceal the existence of the DTC patients with continuous or recurrent lesions,and reduce its diagnostic value as tumor markers.Clinically,the prevalence of positive TgAb in patient with DTC is about 20-25%,which is about twice as much as the general population.The level of TgAb will gradually decrease with the disappearance of the target antigen that triggers the autoimmune reaction after surgery and ¹³¹I treatment in patients with DTC.It indicates that there may be DTC persistent/recurrent lesions when the level of TgAb is not continuously decreased or increased.It is reported that the existence of TgAb may be related to the recurrence/metastasis of DTC.Therefore,TgAb may be used as a tumor marker in the follow-up of DTC patients after thyroid surgery as well as Tg.Nevertheless,there is no consensus on the application of TgAb in clinical follow-up of DTC patients.Therefore,it is of great significance to study the value of serum TgAb in the follow-up of DTC patients and determine the diagnostic cutoff value.ObjectiveTo explore the influence of serum TgAb value and its changes rate(TgAb after thyroid surgery and ¹³¹I treatment-TgAb before surgery)/TgAb before surgery×100%)after thyroid surgery and ¹³¹I treatment on the prognosis of DTC patients with preoperative positive TgAb,and determine its diagnostic cutoff value,so as to provide theoretical basis for the subsequent treatment and follow-up.Materials and MethodsA retrospective study was conducted on 478 DTC patients with preoperative TgAb positive?Greater than the normal reference upper limit of 115IU/ml?from May2013 to August 2018 in our hospital,including 63 males and 415 females aged 13 to78?41.0±12.1?years.All patients underwent total or subtotal thyroidectomy,¹³¹I ablation treatment and subsequent TSH inhibition treatment,and have complete clinical data.Serum Tg and TgAb under TSH stimulation?TSH>30 IU/mL?,together with cervical ultrasonography,¹³¹I-Dx-WBS were reviewed after 6 months of treatment.Serum Tg,TgAb and cervical ultrasonography were examined every 6to 12 months in the subsequent follow-up.The prognosis of the patients was divided into two groups?persistence/recurrence group and no persistence/recurrence group?according to the follow-up results.Median follow-up time was 24 months?range,9-63 months?.The cutoff value of the TgAb and its change rate for the diagnosis of DTC persistence/recurrence was determined according to The receiver-operating characteristic?ROC?curve,and the influence of different change trends on the prognosis of DTC patients was analyzed at the same time.To compare the diagnostic efficacy of the cutoff value of TgAb and the change rate.COX proportional risk regression model was used to evaluate the influence of cutoff value of serum TgAb and changes rate on the prognosis of DTC patients with TgAb positive.Results1.The disease-free survival rate of patients with positive TgAb after thyroid surgery+¹³¹I was significantly lower than that of patients with negative TgAb?log-rank?²=33.848,P<0.001?.The cutoff value of TgAb for diagnosis of DTC persistence/recurrence was 295.2IU/ml,the sensitivity,specificity,positive predictive value,negative predictive value and accuracy were 79.1%,70.6%,30.5%,95.4%and71.8%,respectively.The cutoff value of TgAb change rate was-41.0%,the sensitivity,specificity,positive predictive value,negative predictive value and accuracy were 83.6%,72.8%,33.3%,96.5%and 74.3%,respectively.The rate of DTC persistence/recurrence were 3.5%?11/310?,25.8%?25/97?and 43.7%?31/71?,respectively in the decline rate of TgAb was more than 41.0%,less than 41.0%and TgAb increased?log-rank?²=99.056,P<0.001?.Pairwise comparison was statistically significant among the three groups?P<0.017?.2.There was no significant difference in the diagnostic efficacy of DTC persistence/recurrence between the TgAb threshold and the TgAb rate of change threshold?both P>0.05?.The sensitivity,specificity,positive predictive value,negative predictive value and accuracy can be improved to 92.5%,84.7%,49.6%,98.6%and 85.8%,combined two diagnostic methods.There was statistically significant difference compared with the cutoff value of TgAb alone?all P<0.05?.The specificity,positive predictive value and accuracy were statistically differenent compared with the cutoff value of TgAb change rate?all P<0.05?.And there was no statistically differenent in sensitivity and negative predictive value?all P>0.05?.3.The TgAb threshold?RR=2.858,95%CI 1.484-5.502,P=0.002?and rate of change threshold?RR=6.017,95%CI 2.940-12.314,P<0.001?are independent risk factors for the persistence/recurrence of DTC patients with positive TgAb.Conclusion1.TgAb value and rate of change after thyroid surgery+¹³¹I treatment can be used to monitor the persistence/recurrence of DTC.The diagnostic cutoff value was295.2IU/mL,-41.0%,respectively.2.The diagnostic efficacy of DTC persistence/recurrence between TgAb threshold and rate of change threshold are equivalent.The diagnostic accuracy can be improved when combined.3.The TgAb threshold and rate of change threshold are independent risk factors for persistence/recurrence of DTC patients with positive TgAb.