individualize our patient doses of thyroxine and optimize those doses and clearly, as you heard this morning, small changes in a dose can cause significant clinical effects. Like Dr. Tuttle, who you heard this morning, I specialize in thyroid cancer and it's very important for my patients to have their TSH levels exactly titrated to where we want it. The manufacturers facilitate this need of the clinician by providing 12 different dosage strengths. Differences as little as 9 or 10 percent between these doses can make a big difference for our patients.
You heard also this morning of entities of mild thyroid failure or mild hyperthyroidism. In these entities, the serum T4 levels, either free or total, are normal or within the reference range, but in the case of mild thyroid failure, the TSH is slightly elevated, in mild hyperthyroidism, the TSH is suppressed. These two entities are a model and correlate exactly with our patients who are taking exogenous replacement thyroxine.
The importance of these slight differences are illustrated by this study that you've seen already twice this morning. This was a study by Carr in the U.K. that looked at a group of hypothyroid individuals and optimized