Thyroid disorders are common, affecting more than 10% of people in the US, and laboratory tests are integral in the management of these conditions. The repertoire of thyroid tests includes blood tests for thyroid-stimulating hormone (TSH), free thyroxine, free triiodothyronine, thyroglobulin (Tg), thyroglobulin antibodies (Tg-Ab), thyroid peroxidase antibodies (TPO-Ab), TSH receptor antibodies (TRAb), and calcitonin. TSH and free thyroid hormone tests are frequently used to assess the functional status of the thyroid. TPO-Ab and TRAb tests are used to diagnose Hashimoto's thyroiditis and Graves' disease, respectively. Tg and calcitonin are important tumor markers used in the management of differentiated thyroid carcinoma and medullary thyroid carcinoma (MTC), respectively. Procalcitonin may replace calcitonin as a biomarker for MTC. Apart from understanding normal thyroid physiology, it is important to be familiar with the possible pitfalls and caveats in the use of these tests so that they can be interpreted properly and accurately. When results are discordant, clinicians and laboratorians should be mindful of possible assay interferences and/or the effects of concurrent medications. In addition, thyroid function may appear abnormal in the absence of actual thyroid dysfunction during pregnancy and in critical illness. Hence, it is important to consider the clinical context when interpreting results. This review aims to describe the above-mentioned blood tests used in the diagnosis and management of thyroid disorders, as well as the pitfalls in their interpretation. With due knowledge and care, clinicians and laboratorians will be able to fully appreciate the clinical utility of these important laboratory tests.
Antibodies ; Biomarkers, Tumor ; Calcitonin ; Critical Illness ; Diagnosis ; Graves Disease ; Hematologic Tests ; Iodide Peroxidase ; Physiology ; Pregnancy ; Receptors, Thyrotropin ; Thyroglobulin ; Thyroid Function Tests ; Thyroid Gland* ; Thyroid Neoplasms ; Thyroiditis ; Thyrotropin ; Thyroxine ; Triiodothyronine

Primary hyperparathyroidism (PHPT) is a common endocrine condition, increasingly presenting asymptomatically and detected on routine laboratory examination in developed countries. Multiple spontaneous tendon ruptures as the initial presentation of PHPT is extremely rare. We present the case of a 28-year-old male diagnosed with severe hypercalcemia secondary to PHPT after presenting with complications of multiple spontaneous tendon ruptures,and discuss the management issues in PHPT for this patient.
Hyperparathyroidism, Primary ; Hypercalcemia

Synthetic thyroxine has replaced animal thyroid gland extract as the preferred drug in chronic thyroid hormone replacement. Synthetic thyroxine monotherapy is used to treat overt primary and secondary hypothyroidism, and some cases of subclinical hypothyroidism. In addition, thyroid-stimulating hormone suppressive therapy with thyroxine is a component of the chronic treatment for differentiated thyroid carcinoma. Liothyronine, however, is conventionally for short-term usage, including thyroid hormone withdrawal preparation for radioactive iodine scanning and treatment of differentiated thyroid carcinoma and some cases of myxoedema coma. On very rare occasions where patients are apparently intolerant of or unresponsive to thyroxine, liothyronine may be used chronically. However, there is controversy concerning the use of alternative regimens of thyroid hormone, such as the use of thyroxine-liothyronine combination and thyroid extracts. Thyroid hormone has also been misused to promote weight loss and treat 'symptomatic' biochemically euthyroid patients. There is insufficient evidence to support the use of thyroid hormone to improve treatment response in depression and severe non-thyroidal illnesses.
Animals ; Depression ; drug therapy ; Hormone Replacement Therapy ; adverse effects ; methods ; Humans ; Hypothyroidism ; drug therapy ; Thyroid Function Tests ; Thyroid Hormones ; adverse effects ; therapeutic use ; Thyroid Neoplasms ; drug therapy