Frequency and clinical importance of anti-Tg auto-antibodies (ATG).

Abstract

To note the frequency of anti thyroglobulin autoantibodies (ATG) and its clinical importance in 25 follow-up cases of differentiated thyroid cancer (DTC). A case control study. The total duration of study was one year (September 2000 to August 2001). Majority of the patients included were the routine follow-up cases at IRNUM, Peshawar. However, few of the cases were also included from NORI, Islamabad and AFIP, Rawalpindi. All the patients who had undergone sub-total or total thyroidectomy followed by I-131 ablation therapy were selected for this study. Thyroglobulin (Tg) and ATG were measured using immunometric assay technique with reference range of non-detectable to 40 IU/L. Patients with serum Tg level 10 ng/mL were included in group-1 (n=15) and all the remaining (n=10) in group-2. Overall, 11 patients showed ATG titer above the pre-defined threshold level. In group-1 patients, 8 had positive anti-Tg antibodies in their sera while in group-2, it was positive in only 3 cases. Risk of relapsing metastatic/recurrent disease in association with ATG was calculated which showed that patients with positive ATG have almost seven-fold increased risk of having recurrent/metastatic disease than those who do not. Samples for s-Tg measurements must also be evaluated for ATG status because more than one-third of these patients have positive ATG titer in their sera. Although in the presence of positive ATG, the risk of concurrent metastatic/recurrent thyroid disease is increased but still more studies are required to support its significance.