Variability of response to thyroid-releasing hormone in normal elderly

The present study was undertaken to define the hormonal response to thyroid-releasing hormone (TRH) further in a large, healthy, ambulatory elderly group. Seventy-seven subjects over 60 years old, 30 males (MA) and 47 females (FA), and control subjects, 22 males (MC) and 42 females (FC) were studied. No difference in thyroxine (T4), free thyroxine index (FT4I), baseline prolactin, and thyrotropin (TSH) concentrations were found between the four groups. Tri-iodothyronine resin uptake was only different between MC and FA groups. Post-TRH, TSH concentrations were higher in control males and females (MC + FC), compared to their aged counterparts (MA + FA), (P less than 0.05). This was, in part, due to a large number of female controls who exhibited a hyper-response to TRH (delta TSH greater than 35 microU/ml). A blunted response, defined as a delta TSH less than 6 microU/ml, occurred in 36.7% of MA, 29.8% FA, 13.6% MC, and only 4.8% of FC subjects. As expected, there was a significantly higher response of prolactin to TRH in all females (P less than 0.01) than in males; but no age-related difference among the female population was seen. These data indicate that the response of TSH to TRH declines with age, blunting of the response increases with age, and that TRH use has an extremely limited role as a diagnostic test, especially in an elderly population.