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Testing

 

New Test To Detect Thyroid Disease is Faster And More Accurate

Thyroid; 29 Jul 2007   

A new faster and more accurate way to measure thyroid hormones has been developed by researchers at Georgetown University Medical Center.

According to the American Association of Clinical Endocrinologists, approximately 27 million Americans have thyroid disease. 

They state that there have long been concerns that the common "immunoassay" test now in use worldwide is neither specific nor very accurate.

The researchers tested the method they had developed and found that it was far superior to the immunoassay, and just as good as a very expensive, time-consuming, but very accurate laboratory analysis that is less commonly used.
"This is a very specific test and is not plagued by the false readings that make the currently used immunoassay test notoriously inaccurate," said one of the study's investigators, Jacqueline Jonklaas, M.D., Ph.D., assistant professor in the Department of Medicine. "After further confirming studies, we believe this new assay will become the test of choice in most clinical situations."

The test to measure thyroid hormones, which uses tandem mass spectrometry, was developed by Steven Soldin, Ph.D. FACB, a professor at Georgetown University Medical Center in the Departments of Medicine, Pharmacology and Oncology and Director of both the Georgetown Bioanalytical Core Laboratory and Children's National Medical Center Chemistry Laboratory. “Versions of the tandem mass spectrometry technology that can measure free thyroxine (FT4) levels in blood are already in use at a number of medical centers,” says Dr. Soldin, a co-author.

The new test was used to measure thyroxine in blood of 98 pregnant women as well as 29 women who were not pregnant. The investigators used three different tests -- immunoassay, the Georgetown tandem mass spectrometry, and the "gold standard" laboratory test known as equilibrium dialysis -- to measure the hormone in blood samples donated by the volunteers. They found that, across all stages of pregnancy, there was almost total agreement between mass spectrometry and equilibrium dialysis, but immunoassay results differed significantly.

"Pregnancy is the most difficult situation in which to measure thyroxine, and if this test can perform so well in these conditions, it can likely be used for all other clinical needs," Jonklaas said. "We think our treatment of hyperthyroidism and hypothyroidism would be much more accurate if we combined TSH testing with tandem mass spectrometry instead of with the immunoassay," Jonklaas said.

The reason the mass spectrometry test is so accurate is because it measures the thyroxine molecule specifically and uses a filtering system to separate out the "free" thyroxine -- the form that is active -- from deactivated thyroxine that is bound to proteins, Soldin said. The direct/analogue immunoassay test, on the other hand, doesn't separate the two forms, but uses a mathematical formula to come up with a result, he said. "It is so cheap and quick to use, but it provides a number that can be wrong almost half the time."


 

The Evidence for a Narrower Thyrotropin Reference Range Is Compelling

Leonard Wartofsky and Richard A Dickey

Department of Medicine, Washington Hospital Center, Washington, D.C. 20010; Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814; and Georgetown University School of Medicine, Washington, D.C. 20006
Journal of Clinical Endocrinology and Metabolism Vol. 90, No. 9 5483-5488

Debate and controversy currently surround the recommendations of a recent consensus conference that considered issues related to the management of early, mild, or so-called subclinical hypothyroidism and hyperthyroidism. Intimately related to the controversy is the definition of the normal reference range for TSH. It has become clear that previously accepted reference ranges are no longer valid as a result of both the development of more highly sensitive TSH assays and the appreciation that reference populations previously considered normal were contaminated with individuals with various degrees of thyroid dysfunction that served to increase mean TSH levels for the group. Recent laboratory guidelines from the National Academy of Clinical Biochemistry indicate that more than 95% of normal individuals have TSH levels below 2.5 mU/liter. The remainder with higher values are outliers, most of whom are likely to have underlying Hashimoto thyroiditis or other causes of elevated TSH. Importantly, data indicating that African-Americans with very low incidence of Hashimoto thyroiditis have a mean TSH level of 1.18 mU/liter strongly suggest that this value is the true normal mean for a normal population. Recognition and establishment of a more precise and true normal range for TSH have important implications for both screening and treatment of thyroid disease in general and subclinical thyroid disease in particular.


 

Is it safe for patients taking thyroxine to have a low but not suppressed serum TSH concentration?

Graham Leese & Robert Flynn
University of Dundee, Tayside, UK

There has been some new research that shows it may be safe to have lower TSH levels than is recommended at present.

The research was presented at the Society for Endocrinology BES meeting in Manchester and shows that it may be safe for patients to take more thyroxine than currently recommended, which is a lifeline for many people contacting us at the moment because many doctors are reducing their dosages because their TSH is “too low”.

Up until now, doctors believed that too  low a TSH level caused conditions such as heart disease and osteoporosis.

Dr Leese led a team of researchers who examined patients on levothyroxine and studied how variations in their TSH levels affected their long-term health.

16,426 patients taking levothyroxine were followed and it was found that patients with very high (more than 4.0) or suppressed (less than 0.03) TSH levels more frequently suffered from heart disease, abnormal heartbeat patterns and bone fractures than those whose TSH level was in the normal range (0.04 - 4.0). Patients who had a slightly low TSH (0.04 - 0.4) did not have an increased risk of getting these conditions.

In their Media Release of 16th March 2010, the Society for Endocrinology state, “These results show for the first time that it may be safe for patients taking long-term thyroxine replacement therapy to have a low but not suppressed TSH level.  These patients do not show an increased risk of suffering from heart disease, bone fractures or abnormal heartbeat patterns.  This means that patients may be able to take slightly higher doses of thyroxine than are currently recommended without having an adverse effect on their health.”