Thyroid Function Testing-(Quite Technical)

[Guest guest]

Actually the TSH is the best single screening indicator as it is

the " Thermostat " that senses if the body needs the thyroid gland to

turn on or off. The next best test is the Free T4 test as this is a

measure of the actually biologically active Thyroid Hormone.

I am getting a little technical here.

This whole process in a person involves 3 endocrine glands. This is

known as the " Hypothalamic-Pituitary-Thyroid Axis " . We will not

discuss certain genetic binding protein abnormalities here that make

things even more confusing.

In a normal person this is how it works:

The Thyroid produces T3 and T4. However, 99.97% of the total T4/T3

is

bound to protein in the blood. That is not biologically active.

Only

0.03% is in the Free forms that have biologic activity. The Free

T4/T3

flows through the blood stream and the Hypothalamus gland senses the

level of Free T4/T3 (kind of like a thermostat) and if Free T4/T3

falls

below the expected set point, the Hypothalamus makes and pushes TRH

into the blood stream.

The TRH level is sensed by the Pituitary Gland, again like a

thermostat, and if below the set point, the Pituitary produces TSH.

The TSH floats through the blood stream and its level is sensed by

the

Thyroid Gland. When the TSH goes up it turns the Thyroid gland on

with

production of T4/T3.

Then the whole thing starts over again, in reverse. T4/T3 reaches the

set point in the Hypothalamus, turning off TRH. This in turn reaches

the Pituitary and when its Set Point is reached turns off the TSH

production. Then the TSH level is sensed by the Thyroid gland and

when

its set point is reached turns off T4/T3 Production.

Most of the endocrine glands work on the same general principles with

different hormones, with the Hypothalamus and Pituitary glands being

the Controllers.

Primary Hyperthyroidism - Too much T4 and T3 being produced by the

Thyroid Gland. In this case the Thyroid ignores the TSH hormone

being

produced in the Pituitary and just produces T4 and T3 " willy nilly " .

(most common)

Secondary Hyperthyroidism - The Pituitary puts out too much TSH which

is telling the Thyroid to push more T4 and T3 and it does. (second

most

common, but rare, usually a TSH producing tumor)

Tertiary Hyperthyroidism - The Hypothalamus, ignoring feedback from

the

other 2 glands, puts out too much TRH telling the Pituitary to push

TSH

which in turn tells the Thyroid to produce more T4 and T3. (rare,

Usually a TRH producing tumor)

Grave Disease – The immune System produces an antibody that the

Thyroid

gland thinks is TSH, so the Thyroid continuously produces T4 and T3

Hypothroidism - Most common is Hashimoto's which is an antibody

marker

that can be tested for. (most common form of Hypothryroidism)

Next most common form of Hypothyroidism is Primary in that the

Thyroid

gland is simply not able to produce the T4/T3 that is needed.

As in Hyperthyroid conditions, the pituitary or Hypothalamus might be

unable to produce its hormone with the end result being that the

Thyroid gland is not producing T4/T3.

NOW - For anyone who actually managed to read through this entire

discertation and managed to also stay awake....CONGRATULATIONS!

Tom from PA

>

> Vivi,

>

> What test for hypo are you getting? Just TSH?

>

> You should be tested for antibodies, which can indicate

Hashimoto's.

> You should also have your T3 and T4 tested as those hormones are

> better indicators of thyroid issues than TSH. The medical machine

> didn't use to recognize T3 and T4, only " alternative " docs did, but

> now most of the docs I run into have no problem running those for

me

> and then adjusting my meds (Unithroid - T4, Cytomel - T3) according

to

> that and not my TSH.

>

>

> Houston, TX

>