dramatic effects on the target that we've been talking about, the serum TSH. So, serum TSH in patients' symptoms, not serum T4, are therapeutic endpoints that we are using in clinical practice.
The true normal range for TSH, as was mentioned by Dr. Wood, is quite narrow at .5 to 2. Small changes in administered levothyroxine, as I've shown, 10 to 20 percent, can result in significant changes in serum TSH. An abnormal TSH, again as you have heard, has consequences. There's definitely a burden and consequences in the patient if this is not adjusted over a period of time, and there can also be a burden on the health care system by frequent testing, by utility of resources if the TSH is changing and the patient's symptoms are changing.
DR. KIBBE: Thank you.
I believe our next speaker is Dr. Irwin Klein.
DR. KLEIN: Yes. Good morning.
DR. KIBBE: Good morning.
DR. KLEIN: By way of introduction, I'm Dr. Irwin Klein, Professor of Medicine and Cell Biology at NYU