(16) Prevalence of Hypothyroidism in The United States: An NHANES 2009–2010 and 2011–2012 Analysis

Publication Number: 347

Background: Hypothyroidism (HT) prevalence in the United States (US) was last estimated at the population level utilizing NHANES III data (1988-1994), some 28 years ago. In this study, using NHANES data from the '09/10 & 11/12 cycles, we demonstrate that the prevalence of HT has grown substantially higher

Objectives: Update estimates of HT prevalence in the US by analysis of the most recent available NHANES data with thyroid profile, the '09/10 & 11/12 cycles.

Methods: Survey data from the '09/10 & ‘11/12 NHANES cycles were combined. Patients aged ≥12 years old were included in the NHANES thyroid profile sub-sample; women who were pregnant were excluded. Disease status was determined from blood samples or evidence of HT treatment. Overt HT was defined as presence of elevated thyroid-stimulating hormone (TSH >4.0 mIU/L) and a subnormal or low level of free thyroxine (FT4 < 0.8 ng/dL); patients with a documented prescription for HT treatment were also categorized with overt HT regardless of lab values. Subclinical HT was defined as elevated TSH (>4.0 mIU/L) and normal FT4 (≥0.8 ng/dL), without a documented prescription for HT treatment. Disease-free patients had TSH levels of 0.4 - 4.0 mIU/L and no prescription for HT treatment. Eligible HT therapies were levothyroxine, liothyronine. The results were analyzed by available demographic & comorbidity data.

Results: Overall, HT prevalence (overt or subclinical) is estimated to be 9.6%, compared to 4.6% cited from the previous NHANES study. Prevalence among women (12.9%) was twice that of men (6.1%). When stratified to only include patients with TSH >4.5 mIU/L, as was done in the previous NHANES study, the prevalence of overt HT based on laboratory results changed from 2.1% to 2.0% (n=4,988,115), which was substantially higher than reported prevalence of 0.3% in the previous NHANES study, and subclinical HT prevalence changed from 1.4% to 0.9% (n=2,288,406). When broken up by NHANES cycle, prevalence of HT generally remained stable between the '09/10 & ‘11/12 surveys. Prevalence of overt HT, defined by laboratory results, remained stable at 2.1% (n=5,419,103 in '09/10; n=5,343,292 in ‘11/12); prevalence based on hypothyroid drug prescriptions decreased slightly from 6.4% (n=16,228,763) to 5.9% (n=15,113,005). Prevalence of untreated subclinical HT increased from 1.1% (n=2,727,223) to 1.7% (n=4,274,134) between the two survey cycles. Overall, HT prevalence remained stable at 9.7% (n=24,375,089) in '09/10 and 9.6% (n=24,730,431) in ‘11/12.

Conclusions: This study provides important updates to the epidemiology of HT. Since the last systematic evaluation, prevalence of HT has substantially increased in the US based on updated NHANES data. These results are part of a larger study including analysis of claims data for more current estimates.