Effect of a sensitive thyrotropin-stimulating hormone assay on dosing of L-thyroxine

The Wisconsin Veterans Home has had a special interest in thyroid disease since 1986. Until recently, dosage adjustment of L-thyroxine in residents with primary hypothyroidism was accomplished by individual physicians guided by standard thyroid function tests. A shift to a sensitive thyrotropin-stimulating hormone (TSH) assay provided an opportunity to assess the frequency of sensitive TSH suppression secondary to excessive doses of L-thyroxine which would not be recognized by the standard TSH assay. We reviewed the charts of 46 residents who were not acutely ill and had been in the facility at least 6 months. Sensitive TSH was determined while on a stable dose of L-thyroxine for a minimum of 6 weeks. Six residents (13%) had low sensitive TSH levels indicating an excessive dose of L-thyroxine. The application of the sensitive TSH assay resulted in dose reduction.