The Clinical Significance of Subclinical Thyroid Dysfunction

• Published in: Endocrine reviews Vol. 29; no. 1; pp. 76 - 131
• Main Authors: Biondi, Bernadette, Cooper, David S
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Endocrine Society 01.02.2008; Copyright by The Endocrine Society
• Subjects: Adolescent; Adult; Aged; Aged, 80 and over; Aging; Biological and medical sciences; Calcification, Physiologic; Cardiovascular Diseases; Child; Child, Preschool; Cognition; Diagnosis, Differential; Endocrinopathies; Fundamental and applied biological sciences. Psychology; Humans; Hyperthyroidism - diagnosis; Hyperthyroidism - physiopathology; Hyperthyroidism - therapy; Hypothalamus; Hypothyroidism - diagnosis; Hypothyroidism - physiopathology; Hypothyroidism - therapy; Infant; Infant, Newborn; Medical sciences; MEDLINE; Middle Aged; Neonatal Screening; Non tumoral diseases. Target tissue resistance. Benign neoplasms; Pituitary Gland; Quality of Life; Reference Values; Risk Factors; Thyroid Diseases - blood; Thyroid Diseases - diagnosis; Thyroid Gland; Thyroid. Thyroid axis (diseases); Thyrotropin - blood; Thyroxine - blood; Triiodothyronine - blood; Vertebrates: endocrinology; Replacement therapy; Endocrine gland; Adenohypophyseal hormone; Dysfunction; Thyroid stimulating hormone; Thyroid gland; Review
• ISSN: 0163-769X; 1945-7189
• DOI: 10.1210/er.2006-0043

Subclinical thyroid disease (SCTD) is defined as serum free T4 and free T3 levels within their respective reference ranges in the presence of abnormal serum TSH levels. SCTD is being diagnosed more frequently in clinical practice in young and middle-aged people as well as in the elderly. However, the clinical significance of subclinical thyroid dysfunction is much debated. Subclinical hyper- and hypothyroidism can have repercussions on the cardiovascular system and bone, as well as on other organs and systems. However, the treatment and management of SCTD and population screening are controversial despite the potential risk of progression to overt disease, and there is no consensus on the thyroid hormone and thyrotropin cutoff values at which treatment should be contemplated. Opinions differ regarding tissue effects, symptoms, signs, and cardiovascular risk. Here, we critically review the data on the prevalence and progression of SCTD, its tissue effects, and its prognostic implications. We also examine the mechanisms underlying tissue alterations in SCTD and the effects of replacement therapy on progression and tissue parameters. Lastly, we address the issue of the need to treat slight thyroid hormone deficiency or excess in relation to the patient’s age.