Thyroid hormone therapy initiation is common after hemithyroidectomy, affecting nearly 40% of previously euthyroid adults within two years, with preoperative TSH and thyroid cancer being the strongest predictors.
Key Findings
Results
Within 24 months of hemithyroidectomy, 39.7% of previously euthyroid adults required thyroid hormone therapy initiation or developed overt biochemical hypothyroidism.
Study included 8,467 eligible patients from Clalit Health Services (2003-2020)
3,362 patients (39.7%) reached the primary endpoint within 24 months
The primary endpoint was defined as first levothyroxine dispensing or overt biochemical hypothyroidism within 24 months
Inclusion criteria required preoperative TSH < 5.0 mIU/L, no preoperative thyroid hormone therapy, and at least two years of follow-up
Results
The majority of thyroid hormone therapy initiations after hemithyroidectomy occurred early, with 25.7% of all patients initiating by 4 months and 36.6% by 12 months.
2,179 patients (25.7%) initiated therapy by 4 months post-surgery
3,100 patients (36.6%) initiated therapy by 12 months post-surgery
3,362 patients (39.7%) initiated therapy by 24 months post-surgery
These findings indicate that the treatment burden accumulates rapidly in the early postoperative period
Results
Extended follow-up beyond two years identified an additional 558 initiations, bringing the cumulative rate to 46.3%.
558 additional therapy initiations were identified beyond the 24-month primary follow-up window
The cumulative rate reached 46.3% with extended follow-up
This suggests that the two-year endpoint captures the majority but not all of the treatment burden following hemithyroidectomy
Results
Thyroid cancer was associated with markedly higher rates of thyroid hormone therapy initiation compared to benign disease.
72.7% of patients with thyroid cancer initiated thyroid hormone therapy within 24 months
33.4% of patients without thyroid cancer initiated thyroid hormone therapy within 24 months
Thyroid cancer was the second strongest multivariable predictor with an odds ratio of 4.99 (95% CI, 4.29–5.81)
Results
Preoperative TSH was the strongest multivariable predictor of thyroid hormone therapy initiation after hemithyroidectomy.
Preoperative TSH had an odds ratio of 1.55 per 1 mIU/L increase (95% CI, 1.47–1.64)
This was identified as the strongest predictor in multivariable analysis, exceeding thyroid cancer in per-unit effect
All included patients had preoperative TSH < 5.0 mIU/L, meaning this predictor operated within the normal-to-mildly-elevated euthyroid range
Methods
This was a retrospective population-based cohort study using de-identified electronic health record data from a large Israeli health maintenance organization.
Data were extracted from Clalit Health Services, covering the period 2003–2020
The MDClone research platform was used for data extraction
The study population included adults undergoing hemithyroidectomy who were previously euthyroid with no preoperative thyroid hormone therapy
The large sample size of 8,467 eligible patients supports population-level generalizability within this health system
What This Means
This research suggests that a very common surgical procedure — removing half of the thyroid gland (hemithyroidectomy), often chosen specifically to preserve the body's own thyroid function — results in a surprisingly high rate of patients eventually needing thyroid hormone replacement pills anyway. Studying nearly 8,500 patients over up to 17 years, the researchers found that about 40% of patients who had normal thyroid function before surgery ended up starting thyroid hormone therapy within two years. Most of this occurred quickly: more than a quarter of all patients started treatment within just four months of surgery. When follow-up was extended beyond two years, nearly half of all patients eventually required treatment.
Two factors stood out as the strongest predictors of who would need thyroid hormone therapy after surgery. First, patients who had thyroid cancer were more than four times as likely to need treatment compared to those with benign (non-cancerous) thyroid conditions — more than 70% of cancer patients initiated therapy versus about 33% of non-cancer patients. Second, even within the normal range, patients with higher preoperative TSH levels (a blood test used to assess thyroid function) were significantly more likely to need therapy after surgery, with each 1-unit increase in TSH raising the odds by 55%.
This research suggests that patients and doctors choosing hemithyroidectomy — often to avoid lifelong thyroid medication — should be aware that a large proportion will end up needing that medication anyway, often within months. The findings highlight that preoperative TSH levels and a diagnosis of thyroid cancer can help identify which patients are at highest risk, which could improve shared decision-making and counseling before surgery.
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Wechsler S, Marom T, Oberman B, Fellner A, Reichenberg Y, Pitaro J, et al.. (2026). Thyroid hormone therapy initiation after hemithyroidectomy: treatment burden, timing, and predictors in a population-based cohort.. Endocrine. https://doi.org/10.1007/s12020-026-04707-3