Abstract
BackgroundSubclinical hypothyroidism, commonly caused by Hashimoto thyroiditis (HT), is a risk factor for cardiovascular diseases. This disorder is defined as merely having elevated serum thyroid stimulating hormone (TSH) levels. However, the upper limit of reference range for TSH is debated recently. This study was to determine the cutoff value for the upper normal limit of TSH in a cohort using the prevalence of Hashimoto thyroiditis as “gold” calibration standard.MethodsThe research population was medical staff of 2856 individuals who took part in health examination annually. Serum free triiodothyronine (FT3), free thyroxine (FT4), TSH, thyroid peroxidase antibody (TPAb), thyroglobulin antibody (TGAb) and other biochemistry parameters were tested. Meanwhile, thyroid ultrasound examination was performed. The diagnosis of HT was based on presence of thyroid antibodies (TPAb and TGAb) and abnormalities of thyroid ultrasound examination. We used two different methods to estimate the cutoff point of TSH based on the prevalence of HT.ResultsJoinpoint regression showed the prevalence of HT increased significantly at the ninth decile of TSH value corresponding to 2.9 mU/L. ROC curve showed a TSH cutoff value of 2.6 mU/L with the maximized sensitivity and specificity in identifying HT. Using the newly defined cutoff value of TSH can detect patients with hyperlipidemia more efficiently, which may indicate our approach to define the upper limit of TSH can make more sense from the clinical point of view.ConclusionsA significant increase in the prevalence of HT occurred among individuals with a TSH of 2.6–2.9 mU/L made it possible to determine the cutoff value of normal upper limit of TSH.
Highlights
Subclinical hypothyroidism, commonly caused by Hashimoto thyroiditis (HT), is a risk factor for cardiovascular diseases
Some authors insisted on the conventional value of 4.0–5.0 mU/L as the upper limit of normal thyroid stimulating hormone (TSH) [10], others suggested it narrowed to 2.5–3.0 mU/L [11]
Laboratory assessments Blood samples were collected for testing thyroid function including serum free triiodothyronine (FT3), free thyroxine (FT4) and TSH, thyroid peroxidase antibody (TPAb), thyroglobulin antibody (TGAb) and other biochemistry parameters including total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL), fasting plasma glucose (FPG), uric acid (UA), alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatinine (Cr) and carbon dioxide combining power (CO2CP)
Summary
Subclinical hypothyroidism, commonly caused by Hashimoto thyroiditis (HT), is a risk factor for cardiovascular diseases. This disorder is defined as merely having elevated serum thyroid stimulating hormone (TSH) levels. The upper limit of reference range for TSH is debated recently. Patients with subclinical hypothyroidism have normal level of serum thyroid hormones (T4, T3, FT3, FT4) and elevated TSH. These patienshave a higher incidence of lipid abnormalities, coronary heart disease, psychiatric disorders and pregnancy complications [1–9], their clinical symptoms are very mild. The upper limit of reference range for “normal” TSH has been the focus of debate in the recent decade. There were even data showing that African-Americans had very low incidence of HT
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
