Intended for healthcare professionals

Rapid response to:

Letter

Thyroid function tests and hypothyroidism: Authors' reply

BMJ 2003; 326 doi: https://doi.org/10.1136/bmj.326.7398.1087 (Published 15 May 2003) Cite this as: BMJ 2003;326:1087

Rapid Response:

Throid function tests and hypothyroidism: Serum TSH levels should not be the measure

It can be easily shown from convential control system theory that TSH
should not be the measure used to establish a "norm" in a hypothyroid
patient. It is well established that TSH level is set as a function of a
closed loop feedback system. When control system theory is applied to
model this activity, a variety of scenarios present themselves.
For example, an erroneous assumption usually made by the medical community
is that hypothyroidism is either primary OR secondary, when in fact it
could easily be a combination of both. In such instance, one can imagine
that the TSH level may well be limited by an underresponsive pituitary or
hypothalumus. The result would be that TSH could be driven to zero while
T3 and or T4 levels are still less than optimum for that patient. Thus
TSH can easily become a faulty measure of the desired result - patient
wellbeing.

Competing interests:  
None declared

Competing interests: No competing interests

17 May 2003
Roy J. Mankovitz, Esq.
Director
PatentLab, California 91302