Monitoring
Due to the long half-life of levothyroxine (1 week), thyroid-stimulating hormone (TSH) should be measured 4-6 weeks after initiation of therapy or dosage change.[62][76] Stable patients with normal serum TSH should have TSH measured every 12 months.[55][62] Pregnancy increases thyroid hormone requirements and the dose of levothyroxine may increase accordingly. TSH should be measured every 4-6 weeks in pregnant women on levothyroxine therapy until mid-gestation, then once in each of the second and third trimesters.[56][90]
One meta-analysis estimated that 55% of patients with hypothyroidism received adequate thyroid hormone replacement therapy, and that thyroid hormone was over-replaced in 20% of patients and under-replaced in 24% of patients.[95]
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