Risk factors and timing of postoperative hypothyroidism onset following hemithyroidectomy.

Postoperative hypothyroidism occurred in 54.2% of patients following hemithyroidectomy.

• 166 of 306 patients developed postoperative hypothyroidism.
• All patients had normal preoperative thyroid function (TSH: 0.61–4.23 mIU/L, fT4: 0.93–1.7 ng/dL).
• Patients with prior thyroid surgery or hormone therapy were excluded.
• Postoperative thyroid function was assessed for at least 2 years.

The majority of postoperative hypothyroidism cases were detected early, with 68.7% within 1 month and 95.2% within 1 year of surgery.

• 68.7% of hypothyroidism cases were detected within the first postoperative month.
• 95.2% of all hypothyroidism cases were detected within 1 year postoperatively.
• The study followed patients for at least 2 years to capture delayed onset cases.
• These findings informed recommendations that thyroid function should be monitored for at least 1 year postoperatively.

Preoperative TSH level was a significant independent predictor of postoperative hypothyroidism on multivariate analysis.

• Preoperative TSH level was identified as a significant predictor with P = 1.60 × 10⁻¹⁵.
• The optimal preoperative TSH cutoff for distinguishing euthyroid and hypothyroid groups was 1.82 mIU/L.
• The area under the receiver operating characteristic curve for this cutoff was 0.875.
• A clinically applicable threshold of 2.0 mIU/L was determined for practical use.

Dual positivity for thyroid peroxidase antibody (anti-TPO) and thyroglobulin antibody (anti-Tg) was a significant independent predictor of postoperative hypothyroidism.

• Dual positivity for anti-TPO and anti-Tg antibodies was significant on multivariate analysis with P = 0.0431.
• This finding suggests that autoimmune thyroid disease markers contribute to postoperative thyroid dysfunction risk.
• Single antibody positivity was not specifically identified as a significant predictor in the multivariate model.

Patients with preoperative TSH ≥2.0 mIU/L had a substantially higher rate of postoperative hypothyroidism and hormone replacement therapy requirement than those with TSH <2.0 mIU/L.

• 90.1% of patients with preoperative TSH ≥2.0 mIU/L developed hypothyroidism.
• 29.7% of patients with preoperative TSH ≥2.0 mIU/L required thyroid hormone replacement therapy.
• Only 3% of patients with preoperative TSH <2.0 mIU/L required hormone replacement therapy.
• These findings suggest that patients with preoperative TSH ≥2.0 mIU/L require careful postoperative follow-up, whereas intensive monitoring may be unnecessary for those with TSH <2.0 mIU/L.

The study was a retrospective analysis of 306 patients who underwent hemithyroidectomy for thyroid tumors between 2016 and 2021.

• 306 patients with normal preoperative thyroid function were included.
• Inclusion criteria required TSH between 0.61–4.23 mIU/L and fT4 between 0.93–1.7 ng/dL preoperatively.
• Patients with prior thyroid surgery or prior hormone therapy were excluded.
• The study period spanned 2016 to 2021 with a minimum follow-up of 2 years.