supercoolguy said:
The TSH test is an indirect measure of thyroid function and can be unreliable to monitor thyroid dosage. A more accurate indicator of thyroid function is the
free T3.
Exerpt 1:
TSH REGULATION
TSH production by the pituitary is itself regulated by two things. The first is the level of thyroid hormones in the blood stream which inhibits TSH production by the pituitary, as a negative feedback loop. Secondly, TSH production is stimulated by the action of TRH (Thyrotropin Releasing Hormone), a hormone produced by the hypothalamus in the brainstem. TRH production is itself regulated by thyroid hormone levels in the blood stream, similar to the thermostat analogy above. Increasing thyroid hormone levels inhibits TRH production, and decreasing thyroid hormone levels allows for more TRH production by the hypothalamus. Thus
thyroid hormone production by the thyroid gland is part of a feedback loop called the HPA, the hypothalamic pituitary axis.
DRUGS
Various drugs such as Glucocorticoids (steroids) and opiates may inhibit the HPA axis and decrease TSH production by causing hypothalamic dysfunction or suppression. Many drugs may cause hypotha¬lamic dysfunction, including opiates, alcohol, anti-psychotics, and even inhaled or topical corticosteroids. There are many others. (15)
Exerpt 2:
Various neuropsychiatric disorders and/or
psychoactive drug therapies may be associated with hypothalamic suppression and reduced TSH levels. These include eating disorders, anorexia nervosa, bulimia and depressive illness. (21)
Hypothalamic Dysfunction - hypothalamic-pituitary-thyroid axis suppression in non-thyroidal illnesses
As mentioned above,
various drugs may inhibit the HPA and cause hypothalamic dysfunction resulting in a suppressed TSH. In acutely ill patients, excessive production of glucocorticoids may cause Hypothalamic dysfunction and a paradoxically low TSH. (17) Acti-vation of pro-inflammatory cytokines IL-2, TNF and IL-6 inhibit TRH-TSH synthesis/secretion causing a paradoxically low TSH.(18)
Exerpt3:
the TSH reference range may not be useful to monitor treatment dosage. (42) In other words, when the patient’s dosage of natural thyroid medication provides complete relief of symptoms, the TSH will typically fall below the lab reference range, also called a suppressed TSH. This may disturb the mainstream endocrinologist or primary care clinician who mistakenly believes the dosage is excessive, and the patient is taking too much thyroid medication. The issue can be settled simply by running a Free T3 test which will show that the Free T3 in the normal range, thus excluding any possibility of a “hyperthyroid state”. Unfortunately, most conventional doctors do not have the knowledge to order a free T3 test, and have limited understanding of the thyroid patient. They rely solely on the TSH reference range to adjust thyroid medication dosage.
Source:
The Unreliable TSH Lab Test
By Jeffrey Dach MD
Full doc on next post
LucH