In-House Solid-Phase Radioassay for the Detection of Anti-thyroglobulin Autoantibodies in Patients with Differentiated Thyroid Cancer

Evaluation of Different Methods for the Detection of Anti- Thyroglobulin Autoantibody: Prevalence of Anti-Thyroglobulin Autoantibody and Anti-Microsomal Autoantibody in Thyroid Cancer Patients

Four anti-thyroglobulin autoantibodies (TgAb) assays were evaluated for their reference interval, method agreement, concordance etc. Prevalence of TgAb and anti-thyroid peroxidase was studied in differentiated thyroid cancer (DTC) and control. Reference intervals for TgAb assays varied from method to method due to varied assay designs. For TgAb correlation coefficients ranged from 0.74 to 0.99 whereas concordance ranged from 81 to 96.1%. Prevalence of thyroid antibodies mainly TgAb was increased in DTC primarily in females. Use of sensitive immunoassays is recommended for thyroid autoantibody measurement. Diagnosis and follow-up are difficult in DTC with coexisting thyroid autoimmunity. Hence, careful monitoring with regular surveillance is suggested.

Comparison of Serum Thyroglobulin Levels in Differentiated Thyroid Cancer Patients Using In-House Developed Radioimmunoassay and Immunoradiometric Procedures

Thyroglobulin (Tg) is a proven tumor marker in the follow-up and post-operative management of patients with differentiated thyroid cancer (DTC). All assays for serum thyroglobulin (s-Tg) are based on immunoassays, however, the assay technique has a bearing on the variations seen in the estimations. We studied this using four in-house developed radioimmunoassays (RIA) and immunoradiometric assays (IRMA). Limit of detection, working range, recovery, dilution test, precision profiles and method comparison were evaluated. All four methods were used for the estimation of s-Tg in DTC patients and also compared for their performance using commercially available Tg IRMA kits from DiaSorin and Izotop. The s-Tg values measured by six different immunoassays showed very significant inter-method correlation (0.84-0.99, p < 0.001). However, among the in-house developed assays; the coated tube IRMA showed a better sensitivity and precision at the lower concentration range and hence, is preferable for the routine measurement of s-Tg in patients negative for Tg autoantibodies (TgAb). Although the second generation IRMAs offer practical benefits of having higher sensitivity, shorter turn-around time and convenience of automation, they, unfortunately, also have higher tendency for interference from both TgAb and heterophilic antibodies, if present in the sample. On the contrary, RIA is less prone to such interference and, hence, can be used in patients with TgAb. In order to effectively use this test, it is important that nuclear medicine physicians and endocrinologists understand these intrinsic technical limitations encountered during s-Tg measurement.