Thyroid cancer is the most commonly diagnosed malignancy of the endocrine system, affecting three times more women than men. Following the removal of thyroid, thyroglobulin (Tg), the major precursor to the thyroid hormones, is routinely measured. Detectable levels of Tg after thyroidectomy may suggest incomplete tumor removal or cancer recurrence. Nonetheless, measurement of Tg, to put it simply, is complex.
The complexity arises from the variability among assays and, most importantly, the fact that up to 30% of thyroid cancer patients (and 10% of the general population for that matter) have anti-Tg autoantibodies (TgAb) that potentially interfere with Tg immunoassays, mostly causing false negative results. As a result, TgAb testing has become an indispensable companion of Tg testing.
In a scientific session this morning, “Gaps in Knowledge and Controversies Surrounding Thyroglobulin Measurement and Interpretation,” experts will address the performance of Tg assays, TgAb assays, and offer insights on how laboratorians should approach the complexity of Tg testing.
During recent years one of the major areas of focus of Alicia Algeciras-Schimnich, PhD, a speaker at today’s session, has been the evaluation of the clinical utility of Tg assays. Algeciras-Schimnich believes that there are some misconceptions on the performance of the Tg assays and she feels strongly about the need to educate clinicians and laboratorians on the benefits and disadvantages of the various methodologies available.
“The introduction of mass spectrometry-based methods has revealed limitations of current assays including limitations of the mass spectrometry-based methods” Algeciras-Schimnich said. She will explicate how understanding these limitations is key to providing guidance to clinicians on the most appropriate method to use based on the patient’s TgAb status.
When it comes to Tg quantitation in patients that are TgAb positive, Algeciras-Schimnich will clarify why there really is no perfect method. Each methodology has different limitations: While clinically some Tg assays are more sensitive and less specific in the presence of TgAb, others are more specific and less sensitive.
Mass spectrometry-based methods have helped labs overcome many of the challenges of Tg testing, as they are not susceptible to TgAb interference. However, limit of quantitation of mass spectrometry-based methods need to improve in order for their successful implementation in clinical practice.
This session also will go beyond Tg testing to tackle analytical performance of TgAb assays. Joely Straseski, PhD will help attendees understand the technical advantages and challenges of TgAb measurements that are helpful both to clinicians and laboratorians. While there are multiple methods and commercial assays available to measure TgAb, Straseski believes that comparisons among them are not ideal. She will emphasize the need to understand which test is most appropriate for specific clinical situations and offer strategies for interpreting confusing results.