Primary hypothyroidism is associated with significant metabolic disturbances, including dyslipidemia, insulin resistance, adipose tissue dysfunction, and altered adipokine secretion. Although levothyroxine replacement therapy effectively restores thyroid hormone levels, the extent to which biochemical recovery reflects metabolic improvement remains unclear.

This prospective observational study aims to evaluate changes in serum adipokine levels, including asprosin, adipolin, omentin-1, and visfatin, together with metabolic parameters in newly diagnosed primary hypothyroid patients before and after 8 weeks of levothyroxine replacement therapy. In addition to conventional biochemical markers, multiple cardiometabolic indices related to insulin resistance, lipid metabolism, and hepatic metabolic burden will be analyzed.

The study is designed to investigate whether normalization of thyroid function is accompanied by parallel metabolic recovery and to explore the potential role of adipokine dynamics in adipose-metabolic remodeling during early levothyroxine treatment.

Hypothyroidism is associated with multiple cardiometabolic abnormalities, including dyslipidemia, insulin resistance, adipose tissue dysfunction, altered energy homeostasis, and chronic low-grade inflammation. Although levothyroxine replacement therapy is effective in restoring thyroid hormone levels, metabolic recovery may not occur simultaneously with biochemical normalization of thyroid function.

Adipokines are biologically active molecules secreted by adipose tissue and play important roles in glucose metabolism, lipid regulation, inflammation, and cardiometabolic risk. Among these adipokines, asprosin, adipolin, omentin-1, and visfatin have been associated with insulin resistance, obesity-related metabolic dysfunction, hepatic metabolism, and inflammatory pathways. However, data regarding the dynamic changes of these adipokines after levothyroxine replacement in newly diagnosed primary hypothyroidism remain limited and inconsistent.

This prospective observational study was designed to evaluate changes in serum adipokine levels and metabolic parameters before and after levothyroxine replacement therapy in newly diagnosed primary hypothyroid patients. Serum samples and metabolic measurements will be obtained before treatment initiation and after 8 weeks of levothyroxine therapy.

In addition to conventional thyroid function tests, multiple metabolic indices associated with insulin resistance, lipid metabolism, hepatosteatosis, and cardiometabolic risk will be analyzed, including HOMA-IR, TyG index, METS-IR, AIP, HSI, and Castelli risk indices.

The primary objective of the study is to evaluate changes in adipokine levels following levothyroxine replacement therapy. Secondary objectives include assessing the relationship between adipokine dynamics and metabolic remodeling, insulin resistance, lipid metabolism, obesity phenotype, and hepatic metabolic burden during early biochemical recovery.

Inclusion Criteria:

• Female patients aged 18 years or older
• Premenopausal status
• Newly diagnosed primary hypothyroidism, defined by elevated serum TSH level above the reference range with low free T4 level
• No previous use of levothyroxine or other thyroid hormone replacement therapy
• Ability and willingness to provide written informed consent
• Completion of both baseline and 8-week follow-up assessments

Exclusion Criteria:

• Known hypothalamic or pituitary disease
• Previous thyroid hormone replacement therapy
• Pregnancy or lactation
• Menopause
• History of thyroid surgery or radioactive iodine therapy
• Active malignancy
• Acute or chronic inflammatory disease
• Severe hepatic or renal disease
• Diabetes mellitus
• Use of medications known to significantly affect thyroid function, glucose metabolism, lipid metabolism, or adipokine levels
• Inability or unwillingness to provide informed consent or comply with follow-up requirements

The study population consists of premenopausal female patients aged 18 years or older who were newly diagnosed with primary hypothyroidism at the Internal Medicine outpatient clinic and had not previously received levothyroxine or any other thyroid hormone replacement therapy. Participants were evaluated before treatment initiation and after 8 weeks of standard-of-care levothyroxine replacement therapy. Only patients who completed both baseline and follow-up assessments were included in the final analysis.

Individual participant data (IPD) are not planned to be shared due to institutional and ethical restrictions related to patient confidentiality and biospecimen-based clinical data.