Recovery test for the detection of 'high-dose' hook effect using in-house developed immunoradiometric assay for serum thyroglobulin estimation in differentiated thyroid cancer patients

Thyroglobulin (Tg), is used as a 'tumor marker' in the follow-up of patients with differentiated thyroid cancer (DTC). At RMC, ∼5200 samples are analysed annually for serum Tg estimation using in-house developed one-step immuno-radiometric assay (IRMA), an immunometric assay (IMA); which is rapid, sensitive, automated and cost-effective. However, TgIMA is more prone to interference from Tg autoantibodies (TgAb) and 'high-dose hook effect' which causes underestimation in Tg concentration. Conventionally, TgAb interference is detected by Tg recovery test but as per NACB guidelines for high-dose hook effect detection, every sample needs to be assayed in undiluted and diluted (1/10) form for the measurement of real Tg concentration. This leads to more consumption of reagents and adds to the cost test. This study represents an effort for parallel detection of presence of TgAb interference and hook effect using conventional Tg recovery assay. We perform Tg and 'Tg recovery test' using in-house Tg IRMA kit for detecting Tg and TgAb interference, respectively. We screened patient (n=2389) results and were able to detect presence of hook effect in 91 samples and autoantibody interference in 24 samples by recovery test. It was noted that the presence of hook effect was significantly higher (3.8%) compared to TgAb (1%) by recovery test inference. In conclusion, we mention an extra use of simple, inexpensive Tg recovery assay to recognize recurrent or metastatic disease in DTC patient to avoid a delayed diagnosis and further possible medical implications. Samples were analysed by team in RIA patient services. (author)