Development of In-House IRMA Kit for the Measurement of Serum Thyroglobulin

Thyroglobulin (Tg), is used as a tumor marker in follow-up of patients with differentiated thyroid cancer (DTC) after thyroidectomy and even for long term management after radioiodine therapy. At our Centre, we receive *4800 samples each year for serum-Tg (s-Tg) measurement. Hence, our aim was to develop an in-house Immunoradiometric assay (IRMA) for the estimation of s-Tg in DTC patients who visit for follow-up; as an import substitute for commercial IRMA kits we were using. Standardization of Tg IRMA was carried out using an anti-Tg polyclonal antibody as the capture antibody (raised in camels) and a murine monoclonal antibody labeled with [sup.125]I as the tracer. The monoclonal antibody was produced in-house. Since, anti-Tg autoantibodies are known to cause underestimation of Tg in IRMA system, recovery tests were also conducted. The study showed the standardized in-house-Tg assay has a turnaround time of 18 hours. It has a [B.sub.max] of 35-40% and NSB < 0.2% and was comparable with the commercial kit in respect of assay performance, sensitivity, precision. A very significant (p < 0.001) correlation was observed between in-house Tg assay and the commercial kit for Tg values in serum samples (control and DTC patients) with r value of 0.98. Further the in-house assay and commercial assay showed comparable results for % Tg recovery. After satisfactory evaluation the Tg IRMA kit is now in routine use at our Centre. Since 2013, we have produced 570 kits (100 estimations) and have analyzed approximately 8500 serum samples.