Is "T4 toxicosis" a normal biochemical finding in elderly women?

The lack of equivalence in the distrubtion of normal ranges for free thyroxine index (FT4I) and free triiodothyronine index (FT3I) in the over sixty-five age-group, as compared with the fifteen-sixty-five age-group, supports the idea that "T4 toxicosis" is a common biochemical finding in elderly women. The disparity between FT4I and FT3I ranges was also reflected in the true free T4 and free T3 levels which were measured in some cases. These results suggest that when an increased FT4I is found in an elderly woman with cardiac disease, caution should be exercised in interpreting the result as indicating that thyrotoxicosis is the cause of the cardiac disorder. Estimation of total T3, FT3I, or free T3 seems useful in confirming euthyroidism in such cases.