Diagnosing the Untreated Hypothyroid State
Placeholder lead: thyroid gland underproduces hormone, pituitary TSH climbs.
- 18.4 mIU/L: Baseline TSH (Placeholder: markedly elevated above normal.)
- 0.55 ng/dL: Baseline Free T4 (Placeholder: below the reference interval.)
- 0.4–4.0: Normal TSH range (Placeholder: typical adult reference range.)
- Hashimoto's: Common cause (Placeholder: autoimmune thyroiditis, most frequent cause.)
Feedback loop breakdown
Placeholder: pituitary senses low T4, raises TSH output sharply.
Presenting symptoms
Placeholder: fatigue, cold intolerance, weight gain, bradycardia commonly seen.
Placeholder highlight: untreated hypothyroidism raises cardiovascular and metabolic risk over time.
Weight-Based Starting Dose Selection
Placeholder lead: starting dose scaled to body weight and cardiac risk.
- ~1.6 mcg/kg: Standard starting dose (Placeholder: full replacement in healthy adults.)
- ~0.8 mcg/kg: Elderly/cardiac start (Placeholder: lower dose, start low go slow.)
- 12.5 mcg: Tablet increments (Placeholder: smallest practical dose adjustment step.)
- Empty stomach: Absorption note (Placeholder: take dose fasting for consistency.)
Weight-based calculation
Placeholder: dose (mcg/day) equals weight in kg times factor.
Cardiac risk caution
Placeholder: rapid full-dose replacement can provoke angina, arrhythmia.
Placeholder highlight: elderly and cardiac patients start conservative and titrate slowly upward.
Waiting for Steady State Before Rechecking TSH
Placeholder lead: levothyroxine has a long half-life, needs weeks to equilibrate.
- ~7 days: Half-life (Placeholder: long half-life delays steady state.)
- 6–8 weeks: Recheck interval (Placeholder: minimum wait before dose reassessment.)
- ~5 half-lives: Steady state reached (Placeholder: roughly five weeks to equilibrium.)
- False signal: Early recheck risk (Placeholder: checking too soon misleads titration.)
Why the wait matters
Placeholder: premature labs reflect prior dose, not current one.
What gets measured
Placeholder: TSH primary marker, free T4 confirms direction of change.
Adjusting the Dose Up or Down
Placeholder lead: TSH result drives the next dose adjustment decision.
- Increase dose: TSH high → action (Placeholder: raise by one tablet increment.)
- Decrease dose: TSH low → action (Placeholder: reduce to avoid overtreatment.)
- Tachycardia: Overdose sign (Placeholder: resting heart rate rises with excess hormone.)
- Bone loss: Long-term overdose risk (Placeholder: chronic suppression accelerates osteoporosis.)
Titration step size
Placeholder: smaller, slower steps used in elderly cardiac patients.
Overdose risk signals
Placeholder: suppressed TSH plus symptoms flags over-replacement.
Placeholder highlight: atrial fibrillation risk and bone density loss rise with chronic over-replacement.
Reaching Target Range and Ongoing Monitoring
Placeholder lead: stable maintenance dose found, monitoring continues periodically.
- 0.5–4.5 mIU/L: Target TSH range (Placeholder: euthyroid maintenance target window.)
- Every 6–12 mo: Maintenance recheck (Placeholder: once stable, less frequent testing.)
- Years: Dose stability (Placeholder: maintenance dose often stable long-term.)
- Weight, pregnancy: Recheck triggers (Placeholder: major changes prompt earlier recheck.)
Confirming stability
Placeholder: two consecutive normal TSH values confirm maintenance dose.
Long-term follow-up
Placeholder: annual TSH checks catch drift from weight or age.