Calling captain pituitary ...

In the February 2007 issue of MLO, there is a well-written article entitled "Thyroid function tests: a clinical lab perspective" by Henry Ogedegbe, PhD [p. 10]. Laboratory testing has changed markedly in the past 40 years. In the era of the basal metabolic rate, followed by the time of the protein-bound iodine measurement, the evaluation of thyroid function by laboratory methods was not a simple task for the clinician or the laboratory personnel. Various immunoassays that have developed in the past 30 years have made thyroid testing much more accurate and reliable, and demonstrates very good correlation with the clinical symptoms of the patients.

In my clinical thyroid practice, I have found it extremely difficult to follow patients with thyroid disease who are on replacement-hormone medication utilizing only the TSH value. There is a common misunderstanding, which was repeated in this article, that normalizing the TSH value is the goal in treating patients with thyroid disease. I have found many patients who had a "normal" TSH value while on therapy who were not clinically euthyroid (usually, they are borderline hypothyroid).

Many patients who are taking thyroid medications and are clinically euthyroid will have TSH values in the low normal range near zero. Even though the TSH value is near zero, the [T.sub.4] and [T.sub.3] levels of these patients are almost always within the normal range. Many patients with thyroid disease who have been followed by competent physicians utilizing only the TSH value cannot understand why they still have symptoms of mild hypothyroidism--could be that they are mildly hypothyroid. These patients often are relieved of their hypothyroid symptoms by slightly increasing the dose of thyroid hormone-replacement therapy or by adding triiodothyronine to their replacement regimen.

[ILLUSTRATION OMITTED]

The goal that I strive for in following patients with thyroid disease has always been that they are clinically euthyroid, this usually requires measurement of [T.sub.4], [T.sub.3], and TSH levels as well as a careful review of the patient's history, physical findings, and symptoms.

--William J. Kirsch, MD

Thyroid Disease Consultant

Nason Hospital

Roaring Springs, PA

Dr. Ogedegbe's reply: I agree with the views expressed by the writer that measurement of TSH alone in patients with thyroid diseases who are on hormone-replacement therapy might present difficulties in following such patients. According to the American Association of Clinical Endocrinologists Medical Guidelines for Clinical Practice for the Evaluation and Treatment of Hyperthyroidism and Hypothyroidism, (1) measurement of [T.sub.4] is a more accurate indication of thyroid status than serum TSH in patients treated for hyperthyroidism and/or those on hormone-replacement therapy. The guidelines consider measurement of sensitive TSH as the best screening test for hyperthyroidism and hypothyroidism and, in most ambulatory situations, it is also considered the test of choice for detecting subclinical thyroid-hormone excess or deficiency. In addition, the guidelines recommend monitoring both TSH and [T.sub.4] for upward of one year in patients with severe hyperthyroidism or hypothyroidism until their conditions stabilize. (1)

The recommendations include a requirement that all patients with subclinical hyperthyroidism should undergo periodic clinical and laboratory assessment to determine individual therapeutic options. Once a suppressed TSH level has been detected in a specific patient, a reassessment is required to ensure that the decreased TSH level is persistent rather than transient. A reassessment of the TSH level along with [T.sub.4] and [T.sub.3] in two to four months is considered good clinical practice. (1)

In cases of overt and/or mild hypothyroidism, an increase in the level of TSH with a normal level of [FT.sub.4] is usually observed. Although measurement of TSH may exclude or confirm a diagnosis of primary hypothyroidisms in patients, it may not identify patients with secondary hypothyroidism, in which TSH might be low, normal, or slightly increased. Thus, in the absence of sensitive TSH assays, a serum [FT.sub.4] and [FT.sub.3] should be used in addition to TSH to diagnose hyperthyroidism. (2)

References

1. American Association of Clinical Endocrinologists Medical Guidelines for Clinical Practice for the Evaluation and Treatment of Hyperthyroidism and Hypothyroidism. ACCE Thyroid Task Force, Endocrine Practice. 2002;8(6):458-469

2. Ladenson PW, Singer PA, Ain KB, Bagchi N, Bigos ST, Levy EG, Smith SA, Daniels GH. American Thyroid Association Guidelines for Detection of Thyroid Dysfunction. Arch Inter Med. 2000:160:1573-1575