A publication of the American Thyroid Association

Summaries for Patients from Clinical Thyroidology by Ernest Mazzaferri, MD MACP
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Abbreviations & Definitions

TSH Thyroid stimulating hormone (thyrotropin) is a pituitary hormone that stimulates the release of thyroid hormone from the thyroid gland.TSH levels decrease when the thyroid gland produces excess levels of thyroid hormone.

T4 is thyroxine (the most common circulating thyroid hormone

Subclinical Hypothyroidism An asymptomatic condition in which patients have higher than normal TSH levels with normal serum thyroid hormone levels. A common cause of this is autoimmune thyroiditis (Hashimoto’s disease, especially in women)

What is the study about? The diagnosis and management of subclinical hypothyroidism

The full article title: “Interval between tests and T4 estimation method influence outcome of monitoring of subclinical hypothyroidism..” It is in the May 2008 Issue of Thyroid Volume 93 Issue 5, pages 1634- 40). The authors are J Karmisholt, S Andersen, and P Laurberg. The abstract can be obtained from:

What is known about the problem being studied? Although subclinical hypothyroidism is a common diagnosis, there is no consensus concerning when treatment should be initiated and how untreated patients should be monitored.

What was the aim of the study? This prospective study evaluates the diagnostic reliability of the information obtained from sequential clinical observations and monthly thyroid-function tests measured over a 13 month period.

Who was studied? The study subjects were selected from 34 individuals of mean age 57 years who had serum TSH levels of 5 to 12 μIU/ml (above normal) and thyroxine (T4) and triiodothyronine (T3) within the normal range all of which remained stable on repeated testing over 3 months.

How was the study done? At each visit, serum T4 was measured by three different methods, and signs and symptoms of hypothyroidism were evaluated. The study participants were evaluated monthly for 13 months. Blood samples were obtained and thyroid function tests were determined immediately, and at the end of the study in frozen serum samples stored at –20°C.

What were the results of the study? During the 13-month study period, the criteria for subclinical hypothyroidism were satisfied in 15% to 100% of the patients at various times, and in 29% of the patients during all the visits; the diagnoses were variable 67% of the time. Overall, the hypothyroid score did not differ between patients with overt or subclinical hypothyroidism. Using these observations, subclinical hypothyroidism would have been diagnosed during 74% of the visits, overt hypothyroidism in 22%, and euthyroidism in 4%. The diagnoses also varied according to the three different estimates of T4. Using thyroid-function tests performed every 2nd, 3rd , 4th , 6th or 12th month, resulted in a steady fall in the diagnosis of overt hypothyroidism and a rise in the diagnosis of subclinical hypothyroidism

How does this compare with other studies? A scientific review concluded that data relating a serum TSH level higher than 10 μIU/ml to elevations in serum cholesterol were rated as fair but data relating to benefits of levothyroxine treatment were rated as insufficient. All other associations of symptoms and benefit of treatment were rated as insufficient or absent.

The clinical review concluded that: “Because of the substantial uncertainty concerning the consequences of untreated subclinical hypothyroidism and hyperthyroidism, as well as the benefit of initiating treatment, patient preferences are important in deciding on management of subclinical disease.”

See the web links below that explore the information about this subject:

What are the Limitations of this study? This unique study should be verified in another group of patients

What are the implications of this study? The diagnosis of subclinical hypothyroidism is severely limited by a single set of thyroid function tests and the biologic variation in thyroid testing from visit to visit. Treatment with levothyroxine should be withheld until the diagnosis is verified, but even then it may not be required unless there are extenuation circumstances, particularly patient preference.

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