title: Biochemical Testing of the Thyroid: TSH is the Best and, Oftentimes, Only Test Needed - A Review for Primary Care.
abstract: Disorders of thyroid function are common, and screening, diagnosis, and management are often performed by primary care providers. While management of significant biochemical abnormalities is reasonably straight forward, laboratory tests only slightly outside, or even within, the normal range are becoming more difficult to appropriately manage. A large part of this increasing difficulty in appropriate management is caused by patients requesting, and even demanding, certain tests or treatments that may not be indicated. Symptoms of thyroid dysfunction are non-specific and extremely prevalent in the general population. This, along with a growing body of information available to patients via the lay press and internet suggesting that traditional thyroid function testing is not reliable, has fostered some degree of patient mistrust. Increasingly, when a physician informs a patient that their thyroid is not the cause of their symptoms, the patient is dissatisfied and even angry. This review aims to clarify the interpretation of normal and mild abnormalities of thyroid function tests by describing pituitary-thyroid physiology and through an in depth review of, arguably, the three most important biochemical tests of thyroid function: TSH, free T4, and anti-TPO antibodies. It is important for primary care providers to have an understanding of the shortcomings and proper interpretation of these tests to be better able to discuss thyroid function with their patients.
authors.affiliation: Marshfield Clinic - Weston Center, Department of Endocrinology, Weston, Wisconsin, USA sheehan.michael@marshfieldclinic.org.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Sheehan
mesh_terms: D000328:Adult; D000368:Aged; D000906:Antibodies / Q000097:blood; D001324:Autoantigens / Q000276:immunology; D002940:Circadian Rhythm / Q000502:physiology; D003362:Cost-Benefit Analysis; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood / Q000175:diagnosis*; D007037:Hypothyroidism / Q000097:blood / Q000175:diagnosis*; D007453:Iodide Peroxidase / Q000276:immunology; D033862:Iron-Binding Proteins / Q000276:immunology; D008297:Male; D008875:Middle Aged; D010902:Pituitary Gland / Q000502:physiology; D011320:Primary Health Care / Q000379:methods*; D013959:Thyroid Diseases / Q000097:blood / Q000175:diagnosis; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000502:physiology*; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood; D055815:Young Adult
chemical_list: D000906:Antibodies; D001324:Autoantigens; D033862:Iron-Binding Proteins; D013972:Thyrotropin; C056658:TPO protein, human; D007453:Iodide Peroxidase; D013974:Thyroxine
keywords: Primary care; TSH; Thyroid disease