Levothyroxine Management on the Day of Low-Risk Surgery
Continue levothyroxine on the morning of low-risk surgery without interruption. Levothyroxine does not increase bleeding risk, does not interfere with anesthesia, and maintaining stable thyroid hormone levels is essential to avoid perioperative complications 1.
Rationale for Continuing Levothyroxine
Levothyroxine requires consistent dosing to maintain stable thyroid hormone levels and prevent fluctuations in thyroid status that could complicate perioperative management 1.
Unlike anticoagulants or antiplatelet agents, levothyroxine does not increase surgical bleeding risk and has no known interactions with anesthetic agents that would necessitate holding the medication 1.
The National Comprehensive Cancer Network explicitly recommends that levothyroxine be continued and administered on the morning of surgery 1.
Interrupting levothyroxine therapy could lead to rising TSH levels within days, which is particularly undesirable in thyroid cancer patients requiring TSH suppression but also problematic for any patient requiring stable thyroid function during the perioperative period 1.
Special Considerations for Thyroid Cancer Patients
For differentiated thyroid cancer patients, TSH suppression therapy is a critical component of disease management, and the European Society for Medical Oncology emphasizes maintaining appropriate TSH targets perioperatively 1, 2.
High-risk thyroid cancer patients benefit from TSH suppression to decrease progression of metastatic disease, making uninterrupted levothyroxine therapy even more important 1.
Target TSH levels vary by risk stratification: low-risk patients with excellent response should maintain TSH 0.5–2.0 mIU/L, intermediate-to-high risk patients with biochemical incomplete response should maintain TSH 0.1–0.5 mIU/L, and patients with structural incomplete response require TSH <0.1 mIU/L 3, 2.
Special Considerations for Medullary Thyroid Carcinoma
Medullary thyroid carcinoma (MTC) patients do not require TSH suppression because C cells lack TSH receptors, but they still need levothyroxine replacement to maintain normal thyroid function 1, 2.
TSH should be kept in the normal range (0.5–4.5 mIU/L) through appropriate levothyroxine dosing in MTC patients 1, 2.
Perioperative Safety Profile
Subclinical hypothyroidism (TSH 4.5–10 mIU/L with normal free T4) does not increase perioperative cardiovascular risk in low-risk surgery, and the modest reductions in myocardial contractility observed in studies are not clinically significant 4.
Even TSH >10 mIU/L with normal free T4 allows surgery to proceed safely in low-risk procedures, though the overall clinical context should be assessed 4.
Observational data linking subclinical hypothyroidism to hard cardiac outcomes (myocardial infarction, cardiovascular mortality) are inconsistent and do not justify postponing low-risk surgery 4.
General anesthesia can be safely administered in patients with subclinical hypothyroidism because the modest cardiovascular effects do not contraindicate anesthetic use 4.
Evidence Against Holding Levothyroxine
No randomized controlled trials demonstrate benefit from holding levothyroxine before surgery, and doing so may unnecessarily postpone needed operations 4.
Pre-operative levothyroxine initiation or adjustment does not demonstrably reduce perioperative risk in patients with subclinical hypothyroidism 4.
30–60% of pre-operative TSH elevations normalize spontaneously after surgery, suggesting that transient thyroid dysfunction during the perioperative period is common and self-limited 4.
Post-Operative Management
Re-measure TSH and free T4 3–6 weeks after surgery to assess whether any perioperative thyroid dysfunction was transient 4.
Levothyroxine should be started or adjusted post-operatively if TSH remains >10 mIU/L or if TSH 4.5–10 mIU/L is accompanied by symptoms or positive anti-TPO antibodies 4.
Critical Pitfalls to Avoid
Never hold levothyroxine in thyroid cancer patients requiring TSH suppression, as this could allow TSH to rise and potentially stimulate residual disease 1, 2.
Do not confuse levothyroxine management with medications that genuinely require perioperative interruption (anticoagulants, antiplatelet agents, certain immunosuppressants) 2.
Avoid assuming that all chronic medications need to be held before surgery—levothyroxine is specifically recommended to be continued 1.
Do not delay low-risk surgery to "optimize" thyroid function in patients with subclinical hypothyroidism, as this provides no demonstrated benefit and may harm patients by postponing necessary procedures 4.