our patients describe. These changes, whether they result from change in the dose or in the brand of thyroid hormone, can have important clinical effects on our patients reducing either hyperthyroidism or hypothyroidism.
This chart or this graph demonstrates an experiment that is basically confirmed virtually every day in the offices of clinical endocrinologists; that is, minor changes in the thyroid hormone level, the thyroxine level, in the blood can result in significant changes in the TSH level. Changes of as little as 25 micrograms as shown here can produce significant elevations in the TSH when that is reduced and very low levels of TSH indicating hyperthyroidism when the level is increased.
The importance of these observations is very clear. When the dosage, the source, or the brand of the thyroid hormone replacement is changed, one should recheck the serum TSH levels in 6 to 8 weeks to verify the effectiveness of the new preparation. Changes from one brand or manufacturer of L-thyroxine should be followed by a recheck of serum TSH to verify the equivalence of the medications. When the same dose and the same source of thyroid is used, one needs to recheck these patients only