Abstract and Introduction
Previous estimates determined prevalence of hypothyroidism (HT) to be 4.6% of the US population. This study aimed to update estimates of HT prevalence in the United States by retrospective analysis of 2 datasets. Data on HT type (overt or subclinical HT) and treatment were collected from the 2009–2010 and 2011–2012 National Health and Nutrition Examination Survey (NHANES) cycles. From the Optum administrative claims database, medical and pharmacy claims were collected between January 1, 2012, and December 31, 2019. Patients were defined as having HT if, per given year, they had >1 prescription for HT treatment, >1 claim indicating an HT diagnosis, or thyroid-stimulating hormone levels >4.0 mIU/L (NHANES arm). For both studies, treatment was defined as any evidence of synthetic or natural thyroid hormone replacement, identified by pharmacy claims or patient surveys. Data are reported as percentage of patients with HT and treatments received. Between 2009 and 2012, HT prevalence remained around 9.6% of the US population. The administrative claims dataset showed that HT prevalence grew from 9.5% in 2012 to 11.7% in 2019 and that >78% of patients received thyroxine (T4) monotherapy. Similarly, the NHANES dataset showed that T4 replacement therapy was the most common treatment for HT. From 2012–2019, patients with untreated HT grew from 11.8% to 14.4%. The prevalence of HT in the United States has steadily increased since 2009. Likewise, the percentage of hypothyroid-diagnosed patients not receiving treatment also increased, suggesting that the increased prevalence may be due to increased cases of subclinical HT.
Hypothyroidism (HT) is one of the most common endocrine disorders, with clinical symptoms ranging from mild, such as fatigue, weight gain, cold intolerance, and depression, to more severe manifestations that may include myxedema and death.[1,2]
There are 2 major forms of endogenous HT—primary and secondary. Primary HT occurs when the thyroid cannot produce enough thyroid hormones. In geographic regions with insufficient iodine, primary HT is most often due to iodine deficiency. In iodine-sufficient regions, autoimmune thyroid disease is the most common cause of primary HT. Secondary, or central, HT is less common and generally stems from a dysfunctional pituitary gland or hypothalamus.[1,3] Exogenous HT is commonly a side effect of medications (eg, amiodarone, thalidomide, iodine- or lithium-containing drugs, anti-cancer immunotherapies), surgery, or radiotherapy to the head/neck region.[1,3]
HT can be classified as either overt or subclinical. Overt HT is defined as thyroid-stimulating hormone (TSH) levels above the reference range with free thyroxine (FT4) levels below the reference. Subclinical HT is defined as elevated TSH with normal FT4 levels. Patients with subclinical HT may or may not present with symptoms, thus subclinical HT is typically diagnosed by laboratory tests. There is an ongoing discussion regarding how, if at all, to treat subclinical HT. A wait-and-see strategy is most common among patients with subclinical HT, as up to 4% of patients may go on to develop overt HT.[2,4,5]
The most commonly prescribed treatment for HT is thyroid hormone replacement therapy with levothyroxine, a synthetic form of thyroxine (T4).[1–3,6] Some patients may also be prescribed liothyronine, a synthetic triiodothyronine (T3) replacement therapy, despite clinical trials demonstrating little to no effect on symptoms of HT.[6–8] Indeed, the National Institute for Health and Care Excellence guidelines do not recommend T3 replacement therapy, either alone or in combination with levothyroxine. There is also a subgroup of patients being treated with desiccated thyroid extracts, which are animal-derived versions that contain both T3 and T4 and have demonstrated similar efficacy to that of synthetic replacement therapies.
The most-cited estimation of HT prevalence in the United States stems from analyses of survey data obtained by the National Health and Nutrition Examination Survey (NHANES) from 1988 to 1994 published in 2002. At that time, HT prevalence was estimated to be 4.6% (0.3% overt HT and 4.3% subclinical) of the US population. The NHANES dataset is a robust and diverse sample that combines data from interviews and physical examinations of participants to estimate vital and health statistics of the general US population. As of 2012, the NHANES is no longer collecting thyroid profiles from participants. Estimates of HT have not been systematically updated since those published in 2002, and thus currently cited values may underestimate the true prevalence of HT in the United States and prevent healthcare professionals from adequate screening to facilitate timely diagnosis and treatment.
The aim of this study was to estimate the prevalence of HT in the United States and to determine the proportion of patients receiving HT treatment, as well as the type of therapies most often prescribed. Two methods were used to assess this—data from the 2009–2010 and 2011–2012 NHANES cycles and retrospective data analysis using medical/pharmacy claims data from 2012 to 2019 from the Optum administrative claims database.
J Endo Soc. 2023;7(1) © 2023 Endocrine Society