What are the indications for giving Euthyroz (levothyroxine) to a middle-aged or older woman with primary or secondary hypothyroidism due to thyroid gland failure or pituitary gland dysfunction?

Indications for Euthyroz (Levothyroxine)

Euthyroz (levothyroxine) is indicated for replacement therapy in primary, secondary, and tertiary hypothyroidism, and as adjunctive therapy for TSH suppression in well-differentiated thyroid cancer. 1

Primary Hypothyroidism (Thyroid Gland Failure)

Overt Hypothyroidism

• Initiate levothyroxine immediately when TSH is elevated AND free T4 is below the reference range, regardless of symptom severity 2
• This represents thyroid gland failure requiring prompt replacement to prevent cardiovascular dysfunction, adverse lipid profiles, and quality of life deterioration 2
• All patients with overt hypothyroidism require treatment without exception 3

Subclinical Hypothyroidism (Elevated TSH with Normal Free T4)

TSH >10 mIU/L:

• Treat all patients regardless of age or symptoms, as this threshold carries approximately 5% annual risk of progression to overt hypothyroidism 2, 3
• Treatment may improve symptoms and lower LDL cholesterol, though mortality benefit remains unproven 2

TSH 4.5-10 mIU/L:

• Treat pregnant women or those planning pregnancy to prevent preeclampsia, low birth weight, and neurodevelopmental effects in offspring 2, 3
• Treat symptomatic patients with fatigue, weight gain, cold intolerance, or constipation after a 3-4 month trial with clear benefit evaluation 2
• Treat patients with positive anti-TPO antibodies, as they have 4.3% annual progression risk versus 2.6% in antibody-negative individuals 2, 3
• Treat patients with infertility or goiter 3
• Do NOT routinely treat asymptomatic patients in this range; instead monitor TSH every 6-12 months 2

Special Populations Requiring Treatment

Pregnant Women:

• Treat at any TSH elevation to prevent miscarriage, premature delivery, preeclampsia, and impaired fetal neurocognitive development 2, 3
• Target TSH <2.5 mIU/L in first trimester 2

Patients on Immune Checkpoint Inhibitors:

• Consider treatment even for subclinical hypothyroidism if fatigue or other hypothyroid symptoms are present 2
• Thyroid dysfunction occurs in 6-9% with anti-PD-1/PD-L1 therapy and 16% with combination immunotherapy 2

Elderly Patients:

• Treat TSH >10 mIU/L regardless of age 2
• For TSH 4.5-10 mIU/L in patients >85 years, treatment should probably be avoided based on limited evidence 3

Secondary (Pituitary) and Tertiary (Hypothalamic) Hypothyroidism

Initiate levothyroxine when free T4 is low with inappropriately low or normal TSH, indicating central hypothyroidism 1, 4, 5

Critical Safety Requirement

• Always evaluate and treat adrenal insufficiency BEFORE starting levothyroxine in central hypothyroidism, as thyroid hormone replacement can precipitate life-threatening adrenal crisis 6, 2, 3
• Start hydrocortisone first when multiple pituitary hormones are deficient 6
• If cortisol is low, the increase in cortisol metabolism from thyroid hormone can trigger adrenal crisis 6

Monitoring Approach

• Tailor treatment according to free T4 levels, maintaining them in the upper half of the normal range 3, 5
• TSH cannot be used for monitoring in central hypothyroidism 5

TSH Suppression Therapy for Thyroid Cancer

Levothyroxine is indicated as adjunct to surgery and radioiodine therapy in thyrotropin-dependent well-differentiated thyroid cancer 1

Target TSH Levels by Risk Stratification

• Low-risk patients with excellent response: TSH 0.5-2 mIU/L 2
• Intermediate-to-high risk patients with biochemical incomplete response: TSH 0.1-0.5 mIU/L 2
• Structural incomplete response: TSH <0.1 mIU/L 2

Conditions Where Levothyroxine is NOT Indicated

Explicitly contraindicated uses: 1

• Weight loss or obesity treatment in euthyroid patients
• Suppression of benign thyroid nodules in iodine-sufficient patients (no clinical benefit and risk of iatrogenic hyperthyroidism)
• Nontoxic diffuse goiter in iodine-sufficient patients
• Hypothyroidism during recovery phase of subacute thyroiditis (transient condition)

Critical Confirmation Steps Before Treatment

• Confirm elevated TSH with repeat testing after 3-6 weeks, as 30-60% of elevated TSH levels normalize spontaneously 2
• Measure both TSH and free T4 to distinguish subclinical from overt hypothyroidism 2
• Check anti-TPO antibodies to confirm autoimmune etiology and predict progression risk 2
• Rule out adrenal insufficiency in suspected central hypothyroidism before initiating therapy 6, 2, 3

Common Pitfalls to Avoid

• Never treat based on a single elevated TSH value without confirmation 2
• Never start thyroid hormone before ruling out adrenal insufficiency in central hypothyroidism 6, 2
• Avoid treating transient thyroiditis in recovery phase where TSH elevation is temporary 2
• Do not overlook non-thyroidal causes of TSH elevation (acute illness, medications, recent iodine exposure) 2
• Recognize that approximately 25% of patients on levothyroxine are unintentionally overtreated with fully suppressed TSH, increasing risks for atrial fibrillation, osteoporosis, and cardiac complications 2, 3