Evaluation of Levothyroxine Replacement Therapy After Total Thyroidectomy Using a Smart Wristband

Total thyroidectomy is commonly performed for both benign and malignant thyroid diseases. Following surgery, lifelong levothyroxine replacement therapy is required to maintain euthyroidism. The initial levothyroxine dose is generally determined according to clinical characteristics such as body weight and is subsequently adjusted based on thyroid function tests, which are routinely performed approximately 4 to 6 weeks after surgery. During this period, some individuals may experience symptoms related to under-replacement or over-replacement before biochemical assessment becomes available.

Thyroid hormones have well-established effects on the cardiovascular system. Alterations in thyroid hormone levels can influence heart rate, cardiac rhythm, and autonomic nervous system activity. Recent advances in wearable technology have enabled continuous, noninvasive monitoring of physiological parameters, including nighttime heart rate and heart rhythm. These measurements may provide early physiological changes associated with inadequate thyroid hormone replacement.

The primary objective of this prospective observational study is to evaluate whether nighttime heart rate and heart rhythm data obtained from a smart wristband can identify under-replacement or over-replacement of levothyroxine before the routine postoperative thyroid function assessment. Smart wristband-derived physiological measurements will be compared with serum thyroid-stimulating hormone (TSH) and free thyroxine (fT4) levels obtained during standard postoperative follow-up.

The study will enroll adults undergoing total thyroidectomy who require postoperative levothyroxine replacement therapy. Participants will wear a smart wristband during the early postoperative period while continuing standard clinical care. No experimental intervention or modification of routine treatment will be performed. The findings may help determine whether wearable device-derived physiological data can serve as an early, noninvasive indicator of inadequate levothyroxine replacement and support more timely dose adjustment after total thyroidectomy.

Inclusion criteria

• Age 18 years or older.
• Undergoing total thyroidectomy at the Department of General Surgery, Yeditepe University Faculty of Medicine Hospital.
• Initiation of postoperative levothyroxine replacement therapy as part of routine clinical care.
• Willing and able to attend the routine 1-month postoperative thyroid function test follow-up.
• Willing and able to wear the Xiaomi Smart Band 10 throughout the study period.
• Able to provide written informed consent.

Exclusion criteria

• History of cardiac arrhythmia.
• Current use of beta-blockers or other antiarrhythmic medications that may affect heart rate.
• History of heart failure or advanced cardiovascular disease.
• Diagnosed sleep disorders that may interfere with nighttime heart rate measurements.
• Pregnancy.
• Inability or unwillingness to wear the Xiaomi Smart Band 10 as required.
• Missing clinical or laboratory data required for outcome assessment.
• Refusal to participate or withdrawal of informed consent.