An In-Depth Look at Thyroid Testing

An hour-long AACC webinar on November 20 will feature National Institutes of Health senior scientist and researcher Steven J. Soldin, MD, discussing how liquid chromatography-tandem mass spectrometry (LC-MS/MS) is challenging laboratories to think about thyroid testing in new ways. Soldin’s session will address contemporary issues encountered with thyroid testing, as well as case studies to demonstrate how certain issues can affect patients.

“Current immunoassays for triiodothyronine (T3), free thyroxine (FT4), and free T3 (FT3) are unreliable at both ends of the reference interval,” Soldin explains. “Immunoassays for these analytes do not correlate well with log thyroid stimulating hormone (TSH). Secondly, as immunoassays for T3 and FT3 are unreliable, we cannot properly diagnose the deiodinase deficiencies, conditions that may require dosing with T3 as well as with T4 in order to optimize the patient's clinical condition.”

Also, the definition of subclinical hypothyroidism is an elevated TSH, accompanied by a normal—that is, not low as anticipated—FT4. “When these seemingly normal immunoassay FT4s are repeated using ultrafiltration high-performance LC-MS/MS, two-thirds of them are low (below the 2.5th percentile), agreeing with the elevated TSH result.” Soldin says. “So we believe the TSH and not the immunoassay FT4. Those two-thirds of patients would probably benefit from thyroid hormone replacement therapy, which they are currently not receiving,” adds Soldin, who also holds an appointment as professor of endocrinology and of metabolism and pharmacology at Georgetown University in Washington, DC.

The webinar, which will include a 15-minute question-and-answer session with Soldin, will address how immunoassay and LC-MS/MS methods differ in measuring FT4 versus log TSH; the shortcomings of current immunoassay methodologies, and how they impact the diagnosis and treatment of various thyroid diseases; testing methods for patients with deiodinase deficiencies; what is known about how to correctly diagnose subclinical hypothyroidism re-evaluated with good methodologies; and how to detect and manage the effects of protein abnormalities (i.e., thyroxine binding globulin, albumin and prealbumin) on immunoassays and mass spectrometry assays.