Laboratories rely on different types of immunoassays and, at times, mass spectrometry (MS) to monitor thyroglobulin (Tg) concentrations in thyroid cancer patients and thyroid function during pregnancy. However, complications related to discrepant results and limitations in assay design have made it difficult to guide patient care. Two scientific sessions at the 70th AACC Annual Scientific Meeting & Clinical Lab Expo in Chicago will address these challenges and offer some solutions for labs.
One session on July 31, ( 33103 ) Gaps in Knowledge and Controversies Surrounding Thyroglobulin Measurement and Interpretation, will discuss the pros and cons of Tg and anti-Tg autoantibody (TgAb) methods, offering clinical scenarios involving TgAb-positive and -negative patients. It will take place from 10:30 a.m. to noon and is worth 1.5 CE hours.
Tg and TgAb assays all have different challenges. “Clinically, some Tg assays are more sensitive but less specific in the presence of TgAb while others are more specific but less sensitive,” co-presenters Alicia Algeciras-Schimnich, PhD, DABCC, director of Mayo Clinic’s Clinical Immunoassays Laboratories and chair of its Division of Clinical Biochemistry & Immunology , and Joely Straseski, PhD, MT(ASCP), D(ABCC), FACB, associate professor at the University of Utah School of Medicine and co-director for the automated core laboratory at ARUP Laboratories, Salt Lake City, told CLN Stat. Not all TgAb assays identify the same antibodies, and cutoffs used to define positivity can be controversial.
For Tg, they recommend that labs use an assay with a limit of quantitation (LOQ) of at least 0.1 ng/mL (second generation assays). “This obviates the need to measure Tg under stimulation conditions,” according to Algeciras-Schimnich and Straseski.
For TgAb, labs should use positivity cutoffs based on an assay’s LOQ, rather than the manufacturer’s reference interval, as the latter is often specific for autoimmune thyroid disease. “This will ensure that a greater number of patients who are TgAb positive will be identified. Also labs should select a Tg assay that is minimally affected by TgAb interference and a TgAb assay that detects the most cases of TgAb positivity,” the co-presenters recommended.
Proper utilization of both Tg and TgAb assays is necessary to provide the best patient care with the most effective use of healthcare resources, Algeciras-Schimnich and Straseski suggested.
MS-based methods for measuring Tg have their own advantages in that they’re not susceptible to interferences associated with TgAb. However, to be successful in clinical practice, MS’ limit of quantitation needs improvement, they offered. For now, Tg immunoassays remain the assay of choice for patients who don’t produce TgAb. Compared with most MS and radioimmunoassays, Tg immunoassays have superior sensitivity and are usually more cost-effective and offer faster turnaround times, due to their availability on high-throughput platforms, according to Algeciras-Schimnich and Straseski.
Another session involving thyroid testing will take place August 1, ( 34107 ) Accurate Measurement of Thyroid Hormones in Disease and Pregnancy. Three experts at this scientific session will explore the applications, challenges, and future of these tests.
Discrepant assay measurement results and an absence of uniform evidence-based practice guidelines on using thyroid function tests have hindered clinical and research advancements in this field. “Accurate assessment of thyroid function during pregnancy is difficult, and interpretation of laboratory testing differs from the nonpregnant patient,” according to the session’s summary description.
The American Thyroid Association has tried to remedy these problems by issuing guidelines on diagnosing and treating thyroid disease during pregnancy and the postpartum period. In addition, the Partnership for the Accurate Testing of Hormones (PATH) has been working with key organizations to ensure that the analytical quality of hormone tests meets clinical and public health needs. “As part of its mission, PATH provides technical and scientific support to the Centers for Disease Control and Prevention’s [CDC] hormone standardization program, including identifying high-priority hormones in need of standardization,” session moderator Ronald Whitley, PhD, DABCC, a professor at the University of Kentucky, told CLN Stat.
The next focus for PATH will be standardizing and harmonizing tests for free thyroxine (FT4) and thyroid stimulating hormone (TSH). “CDC is currently developing a reference method for FT4 and is working on certifying FT4 assays in 2019. CDC also supports IFCC [International Federation of Clinical Chemistry and Laboratory Medicine] efforts to standardize thyroid function tests and is coordinating its activities with IFCC to make sure the work conducted by both organizations complement each other,” Whitely said. Additionally, the IFCC Working Group for Standardization of Thyroid Function Tests (C-STFT) has published three reports on standardizing thyroid function tests to resolve method performance and quality specifications issues, and to meet clinical requirements.
During his presentation, Whitely will discuss facilitating the transition to accurate measurement of thyroid hormones. Katleen Van Uytfanghe, PhD, a postdoctoral fellow at Ghent University’s laboratory of toxicology in Belgium, will cover standardization and harmonization of FT4 and TSH measurements while Gregory Brent, BS, MD, a professor of medicine at the David Geffen School of Medicine at UCLA, will explain the clinical challenges of thyroid hormone testing.
After this session, participants will be able to:
- Understand the role of thyroid function biomarkers in clinical decisionmaking;
- Summarize the current state of thyroid hormone testing including analytical performance and its impact on patient care, research translation, and public health;
- Describe activities of the IFCC working group C-STFT to standardize and harmonize thyroid function tests;
- Outline efforts to assess thyroid hormone test performance using certification and accuracy-based proficiency testing; and
- Understand programs and activities of PATH to improve the quality of hormone tests.
This session will take place from 10:30 a.m. to noon and is worth 1.5 CE hours.
Don’t miss these timely sessions on thyroid testing at the 70th AACC Annual Scientific Meeting & Clinical Lab Expo July 29–August 2 in Chicago.