Thyroid diseases represent the most common endocrine abnormalities and it has been estimated that about 20 million levothyroxine prescriptions are dispensed to about 1.8% of the population in the United States annually. Optimal use of valid laboratory tests for the assessment of thyroid status is thus important both medically and economically. In a multi-institute collaborative study, we assessed the performance of thyroid function tests for monitoring and the potential clinical utility of thyroid hormone therapy for suppressing papillary and/or follicular thyroid cancer. The study was carried out by our previously developed method of quantitative research sysnthesis for assessing the efficacy of thyroid hormone suppression therapy on benign solitary thyroid nodules. This approach involves systematic review of the literature for relevant clinical studies and expert opinions, meta-analysis of selected interventional studies, survey of NIH endocrinology practitioners for therapeutic decisions in hypothetical patients with papillary and/or follicular thyroid cancer, practice validation in NIH patients treated with levothyroxine suppression for papillary and/or follicular thyroid cancer, and application of Hill's criteria to asssess causality between thyroid suppression therapy and control of papillary and/or follicular thyroid cancer. In a case study, we investigated the utility of laboratory tests for revealing a clinically important drug-interaction. This drug-interaction occurred due to concomitant ingestion of levothyroxine with high doses of calcium carbonate in the presence of chronic gastrointestinal disorders. Despite different etiologies, initial presentation of this case was similar to our previously described case in which increased doses of levothyroxine replacement therapy were required to achieve euthyroid status in a patient with nephrotic syndrome.
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