Prevalence and risk factors of subclinical thyroid disease

Thyroid Stimulating Hormone Reference Range and Prevalence of Thyroid Dysfunction in the Korean Population: Korea National Health and Nutrition Examination Survey 2013 to 2015

BACKGROUND

No nationwide epidemiological study evaluating the prevalence of subclinical and overt forms of hypothyroidism and hyperthyroidism has yet been conducted in Korea. This study aimed to evaluate the reference range of serum thyroid stimulating hormone (TSH) and the national prevalence of thyroid dysfunctions in Korea.

METHODS

Nation-wide cross-sectional data were analyzed from a representative sample of the civilian, non-institutionalized Korean population (n=6,564) who underwent blood testing for thyroid function and anti-thyroid peroxidase antibody (TPOAb) as part of the Korea National Health and Nutrition Examination Survey VI (2013 to 2015).

RESULTS

The reference interval of serum TSH in the Korean reference population was 0.62 to 6.68 mIU/L. Based on this reference interval, the prevalence of overt and subclinical hypothyroidism was 0.73% (males 0.40%, females 1.10%) and 3.10% (males 2.26%, females 4.04%), respectively. The prevalence of hypothyroidism increased with age until the age group between 50 to 59 years. Positive TPOAb were found in 7.30% of subjects (males 4.33%, females 10.62%). The prevalence of overt and subclinical hypothyroidism TPOAb-positive subjects was 5.16% and 10.88%, respectively. The prevalence of overt and subclinical hyperthyroidism was 0.54% (males 0.30%, females 0.81%) and 2.98% (males 2.43%, females, 3.59%), respectively.

CONCLUSION

The Serum TSH reference levels in the Korean population were higher than the corresponding levels in Western countries. Differences were found in the prevalence of hypothyroidism and hyperthyroidism according to age, sex, and TPOAb positivity. This study provides important baseline information for understanding patterns of thyroid dysfunction and diseases in Korea.

Association between thyroid autoimmunity and Helicobacter pylori infection

BACKGROUND/AIMS

There have been controversial reports linking Helicobacter pylori infection to autoimmune thyroid disease (AITD). However, data regarding the relationship are limited for Asian populations, which have an extremely high prevalence of H. pylori infection. We performed this study to investigate the association between H. pylori infection and AITD in Koreans.

METHODS

This study involved adults aged 30 to 70 years who had visited a health promotion center. A total of 5,502 subjects were analysed. Thyroid status was assessed by free thyroxine, thyroid stimulating hormone, and anti-thyroid peroxidase antibody (TPO-Ab). Immunoglobulin G (IgG) antibodies to H. pylori were measured as an indication of H. pylori infection. We compared the prevalence of TPO-Ab in subjects with and without H. pylori infection.

RESULTS

H. pylori IgG antibodies were found in 2,875 subjects (52.3%), and TPO-Ab were found in 430 (7.8%). Individuals positive for H. pylori Ab were older than those negative for H. pylori Ab (p < 0.01). The proportion of females was significantly higher in the TPO-Ab positive group (41.0% vs. 64.2%, p < 0.01). Prevalence of TPO-Ab positivity was higher in subjects with H. pylori infection (8.6% vs. 7.00%, p = 0.03), and this association was significant after adjusting for age, sex, and body mass index (odds ratio, 1.02; 95% confidence interval, 1.00 to 1.03; p = 0.04).

CONCLUSIONS

In our study, prevalence of TPO-Ab positivity is more frequent in subjects with H. pylori infection. Our findings suggest H. pylori infection may play a role in the development of autoimmune thyroiditis.

Effect of Marijuana Use on Thyroid Function and Autoimmunity

BACKGROUND

Marijuana is legalized for medical use in 24 states and for recreational use in 5. However, effects of marijuana use on thyroid function and autoimmunity are unknown.

METHODS

We performed a cross-sectional analysis of data from the National Health and Nutrition Examination Survey (NHANES) conducted between 2007 and 2012 to assess the effects of marijuana on thyroid function and autoimmunity in users. We included 5280 adults ages 18 to 69 years, who responded to questions related to marijuana use and had laboratory results related to thyroid parameters. Subjects were categorized as nonusers (never used), past users (used prior to 30 days ago), and recent users (used within last 30 days). Using NHANES normative cut offs for thyroid parameters, we compared recent users with nonusers and past users and calculated the odds ratios for the relative rate of clinically significant thyroid dysfunction in those groups. Multivariate logistic regression was then performed to control for confounders.

RESULTS

Fifty-four percent of subjects reported lifetime cannabis use, with 15% using it recently. Univariate regression analysis showed that recent marijuana users had significantly lower frequency of elevated thyrotropin (TSH) and positive anti-thyroperoxidase antibody (TPOAb) versus nonusers/past users. After controlling for confounders, recent marijuana use remained an independent predictor for TSH <5.6 μIU/mL (odds ratio of 0.344 with 95% CI of 0.127-0.928; p = 0.04) but not for negative TPOAb.

CONCLUSION

Recent marijuana use was not associated with thyroid dysfunction but was significantly associated with lower levels of TSH.

Subclinical Hypothyroidism in Childhood Cancer Survivors

PURPOSE

In childhood cancer survivors, the most common late effect is thyroid dysfunction, most notably subclinical hypothyroidism (SCH). Our study evaluated the risk factors for persistent SCH in survivors.

MATERIALS AND METHODS

Survivors (n=423) were defined as patients who survived at least 2 years after cancer treatment completion. Thyroid function was assessed at this time and several years thereafter. Two groups of survivors with SCH were compared: those who regained normal thyroid function during the follow-up period (normalized group) and those who did not (persistent group).

RESULTS

Overall, 104 of the 423 survivors had SCH. SCH was observed in 26% of brain or nasopharyngeal cancer survivors (11 of 43) and 21.6% of leukemia survivors (35 of 162). Sixty-two survivors regained normal thyroid function, 30 remained as persistent SCH, and 12 were lost to follow-up. The follow-up duration was 4.03 (2.15-5.78) years. Brain or nasopharyngeal cancer and Hodgkin disease were more common in the persistent group than in the normalized group (p=0.002). More patients in the persistent group received radiation (p=0.008). Radiation to the head region was higher in this group (2394±2469 cGy) than in the normalized group (894±1591 cGy; p=0.003). On multivariable analysis, lymphoma (p=0.011), brain or nasopharyngeal cancer (p=0.039), and head radiation dose ≥1800 cGy (p=0.039) were significant risk factors for persistent SCH.

CONCLUSION

SCH was common in childhood cancer survivors. Brain or nasopharyngeal cancer, lymphoma, and head radiation ≥1800 cGy were significant risk factors for persistent SCH.

Association of low baseline free thyroxin levels with progression of coronary artery calcification over 4 years in euthyroid subjects: the Kangbuk Samsung Health Study

OBJECTIVE

Overt and subclinical hypothyroidism are risk factors for atherosclerosis and cardiovascular diseases. It is unclear whether thyroid hormone levels within the normal range are also associated with atherosclerosis measured by coronary artery calcium (CAC).

CONTEXT

This study aimed to examine the relationship between normal variations in thyroid function and changes in CAC.

MEASUREMENTS

We conducted a 4-year retrospective study of 2173 apparently healthy men and women with normal thyroid hormone levels. Their free thyroxin (FT4), free triiodothyronin (FT3) and thyroid-stimulating hormone (TSH) levels were measured by electrochemiluminescent immunoassay. The CAC score (CACS) of each subject was measured by multidetector computed tomography in both 2010 and 2014. Progression of CAC was defined as a CACS change over 4 years > 0.

RESULTS

The mean CACS changes over 4 years by quartiles of baseline FT4 level (lowest to highest) were 12·9, 8·43, 7·82 and 7·81 (P = 0·028). CAC progression was not significantly associated with either the baseline FT3 or TSH levels. The odds ratios (OR) for CAC progression over 4 years (highest vs lowest quartile for baseline FT4) were 0·647 (95% confidence interval (CI) 0·472-0·886) after adjustment for confounding factor, which were attenuated with further adjustment for lipid profiles, homoeostasis model assessment of insulin resistance, high-sensitivity C-reactive protein and hypertension [0·747 (95% CI 0·537-1·038)]. Quartiles of baseline FT3 or TSH level did not show any increased OR for CAC progression after adjustment for confounding factors.

CONCLUSIONS

In this cohort of euthyroid men and women, a low baseline FT4 level was associated with a high risk of CACS progression over 4 years.

Distinct Features of Nonthyroidal Illness in Critically Ill Patients With Infectious Diseases

Nonthyroidal illness (NTI), often observed in critically ill patients, arises through diverse alterations in the hypothalamus-pituitary-thyroid (HPT) axis. However, the causal relationship between underlying disease and NTI diversity in critically ill patients is poorly understood.The aim of this study was to examine NTI severity and adverse outcomes in critically ill patients with respect to their underlying disease(s).The medical records of 616 patients admitted to the intensive care unit (ICU) between January 2009 and October 2014 were retrospectively reviewed. Patients with known diseases or taking medications that affect thyroid function were excluded. All-cause mortality (ACM) and length of stay (LOS) in the ICU were assessed as adverse outcomes.The enrolled patients (n = 213) were divided into the following 4 groups according to the severity of NTI at the nadir of their thyroid function test (TFT): normal (n = 11, 5.2%), mild NTI (n = 113, 53.1%), moderate NTI (n = 78, 36.6%), and severe NTI (n = 11, 5.2%). There was no significant difference between the groups in terms of age and gender. NTI severity showed a significantly strong association with ACM (P < 0.0001) and a significant positive association with LOS in the ICU (P = 0.031). After adjusting for age, gender, and current medications affecting TFT, increasing NTI severity led to increased ACM (odds ratio = 3.101; 95% confidence interval = 1.711-5.618; P < 0.0001). Notably, the prevalence of moderate-to-severe NTI was markedly higher in patients with infectious disease than in those with noninfectious disease (P = 0.012). Consistent with this, serum C-reactive protein levels were higher in patients with moderate-to-severe NTI (P = 0.016).NTI severity is associated with increased ACM, LOS, and underlying infectious disease. Future studies will focus on the biological and clinical implications of infectious disease on the HPT axis.

Comparison of universal screening with targeted high-risk case finding for diagnosis of thyroid disorders

OBJECTIVE

Debate about the need for universal screening of thyroid dysfunction in pregnancy is ongoing. The present study aimed to compare universal screening with targeted high-risk case findings for early diagnosis of thyroid disorders in Iranian pregnant women.

STUDY DESIGN

This cross-sectional prospective study was carried out on 1600 pregnant women in their first trimester. A checklist, including all related risk factors recommended by The American Thyroid Association, was completed for all participants. Serum concentrations of thyroxine (T4), T-uptake, TSH and thyroid peroxidase antibody (TPOAb) were measured and thyroid status was documented, based on hormonal measurements and clinical examinations.

RESULTS

There were 656 women (44.3%) that had at least one risk factor for thyroid diseases and were eligible for the targeted high-risk case finding (high-risk group) approach, while 55.7% had no risk factors (low-risk group). Using the universal screening approach, there were 974 women (65.8%) with normal thyroid status and 506 participants (34.2%) with thyroid disturbances, including overt hyperthyroidism (0.7%), overt hypothyroidism (1.1%), subclinical hypothyroidism (30.1%; positive TPOAb (5.5%) and negative TPOAb (24.6%); and euthyroid and positive TPOAb (2.3%). Of women with thyroid dysfunction, 64.4% were in the high-risk group and 35.6% were in the low-risk group (P<0.0001).

CONCLUSIONS

The targeted high-risk case finding approach overlooks about one-third of pregnant women with thyroid dysfunction. If ongoing prospective trials provide evidence on the efficacy of treating subclinical hypothyroidism in pregnancy, in populations with a low prevalence of presumed risk factors, the targeted high-risk case finding approach will be proven inefficient.

Incidence and Prevalence of Overt Hypothyroidism and Causative Diseases in Korea as Determined Using Claims Data Provided by the Health Insurance Review and Assessment Service

BACKGROUND

The incidence and prevalence of overt hypothyroidism have been reported to be 2 to 4/1,000 population/year and 8 to 13/1,000 population, respectively, in foreign countries. As there has been no nationwide survey to obtain data in Korea, the present study investigated the incidence and prevalence of overt hypothyroidism in Korea using claims data provided by the Health Insurance Review and Assessment Service. The proportions of causative diseases for hypothyroidism were also analyzed.

METHODS

This study was retrospectively performed with 541,969 Korean patients (92,832 men and 449,137 women), with overt hypothyroidism, treated with thyroid hormone between 2008 and 2012.

RESULTS

The incidence of overt hypothyroidism in Korea was 2.26/1,000 population/year (0.78 in men and 3.72 in women), and the prevalence was 14.28/1,000 population (4.40 in men and 24.03 in women). When patients with thyroid cancer were excluded, the incidence was 1.56/1,000 population/year (0.54 in men and 2.57 in women). The incidence increased with age, with peaks in and after the late 60s in men and in the early 50s in women. The prevalence peaked in the early 70s in men and in the late 50s in women.

CONCLUSION

This is a report of the first nationwide investigation of the incidence and prevalence of overt hypothyroidism in Korea, although it is limited to patients treated with thyroid hormone.

Subclinical Hypothyroidism and Cardiovascular Disease

Subclinical hypothyroidism (SCH) is a common disorder that is characterized by elevated thyroid-stimulating hormone levels in conjunction with free thyroxine concentrations within the normal reference range. Thyroid hormones are known to affect the heart and vasculature and, as a result, the impact of SCH on the cardiovascular (CV) system has recently become an important topic of research. Strong evidence points to a link between SCH and CV risk factors such as alterations in blood pressure, lipid levels, and atherosclerosis. Additionally, accumulating evidence indicates that SCH is associated with metabolic syndrome and heart failure. The present review proposes that SCH may be a potentially modifiable risk factor of CV disease and mortality. However, large-scale clinical trials with appropriate power investigating the risks and benefits of SCH treatment are required to determine whether these benefits can be achieved with levothyroxine therapy.

Reference interval for thyrotropin in a ultrasonography screened Korean population

BACKGROUND/AIMS

The diagnostic accuracy of thyroid dysfunctions is primarily affected by the validity of the reference interval for serum thyroid-stimulating hormone (TSH). Thus, the present study aimed to establish a reference interval for TSH using a normal Korean population.

METHODS

This study included 19,465 subjects who were recruited after undergoing routine health check-ups. Subjects with overt thyroid disease, a prior history of thyroid disease, or a family history of thyroid cancer were excluded from the present analyses. The reference range for serum TSH was evaluated in a normal Korean reference population which was defined according to criteria based on the guidelines of the National Academy of Clinical Biochemistry, ultrasound (US) findings, and smoking status. Sex and age were also taken into consideration when evaluating the distribution of serum TSH levels in different groups.

RESULTS

In the presence of positive anti-thyroid peroxidase antibodies or abnormal US findings, the central 95 percentile interval of the serum TSH levels was widened. Additionally, the distribution of serum TSH levels shifted toward lower values in the current smokers group. The reference interval for TSH obtained using a normal Korean reference population was 0.73 to 7.06 mIU/L. The serum TSH levels were higher in females than in males in all groups, and there were no age-dependent shifts.

CONCLUSIONS

The present findings demonstrate that the serum TSH reference interval in a normal Korean reference population was higher than that in other countries. This result suggests that the upper and lower limits of the TSH reference interval, which was previously defined by studies from Western countries, should be raised for Korean populations.

Subclinical hypothyroidism in addition to common risk scores for prediction of cardiovascular disease: a 10-year community-based cohort study

OBJECTIVE

This study was carried out to determine whether serum TSH levels improve the prediction of cardiovascular risk in addition to common clinical risk scores, given the association between subclinical hypothyroidism (SCH) and cardiovascular disease (CVD).

DESIGN

We carried out an observational study in a prospective cohort.

METHODS

The study included a total of 344 SCH and 2624 euthyroid participants aged over 40 years and who were without previously recorded CVDs were included in this study analysis. We measured thyroid function and traditional risk factors at baseline and estimated the 10-year cumulative incidence of CVD in a gender-stratified analysis.

RESULTS

During 10 years of follow-up, 251 incident cardiovascular events were recorded. The elevation of serum TSH levels significantly increased the CV risk independent of conventional risk factors in men. In the atherosclerotic CVD (ASCVD) risk score or the Reynolds risk score (RRS) model, the addition of serum TSH levels had no effect on model discrimination as measured by the area under the curve in either women or men. Adding serum TSH did not improve the net reclassification improvement in either women (3.48% (P=0.29) in the ASCVD, -0.89% (P=0.75) in the RRS, respectively) or men (-1.12% (P=0.69), 3.45% (P=0.20), respectively) and only mildly affected the integrated discrimination Improvement in the ASCVD-adjusted model (0.30% in women and 0.42% in men, both P=0.05).

CONCLUSIONS

In the context of common risk scoring models, the additional assessment of serum TSH levels provided little incremental benefit for the prediction of CV risk.

Bone health and clinical results after hip fracture surgery in patients with subclinical hypothyroidism

Background

Subclinical thyroid dysfunction might influence a bone health. We evaluated whether subclinical hypothyroidism adversely affects bone health including bone mineral density (BMD), level of vitamin D, and bone turnover status in patients with hip fracture.

Methods

We evaluated 471 patients aged 50 years or older, who underwent hip fracture surgeries. BMD, level of vitamin D, bone turnover status, and one-year mortality were compared between subclinical hypothyroidism group and control group.

Results

BMD of femur and the level of 25-hydroxy-vitamin D (25-[OH]D) were similar in the two groups. There were no significant differences in bone turnover markers according to thyroid function. No significant differences were observed between the groups in utilization of intensive care unit (ICU), length of hospital stay, mobility, and one-year mortality.

Conclusions

Subclinical hypothyroidism was not associated with reduced bone health, including BMD, the level of 25-(OH)D, and bone turnover marker.