Interpreting Lab Tests For Hyperthyroidism and Graves Disease

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Lab tests for hyperthyroidism include TSH, T3, T4 and thyroid antibodies. These markers need to be looked at together, and with respect to patient symptoms for proper interpretation.

TSH, T3 and T4

As seen in the diagram below, TSH is produced by the hypothalamus and pituitary in the base of the brain. It's job is to tell the thyroid to make more thyroid hormone.

TSH production from hypothalmus and pituitary, simulates the thyroid to make t4

Typical reference ranges for TSH are about 0.4 - 4.0. Nonetheless, a more optimal range woudl be about 1.5 - 2.5. Anything out of that range suggests leaning towards hypo or hyperthyroidism and warrents further investigation.

If the brain senses that thyroid hormone is too low, then it increases production of TSH, to make more thyroid hormone. Therefore, elevated TSH typically implies hypothyroidism.

On the other hand, if thyroid hormone is too high, then TSH drops in order to tell the thyroid to make less hormone. Therefore very low TSH typically implies hyperthyroidism.

Sometimes a low normal TSH indicates a pattern of hypothyroidism called "euthyroid sick syndrome." This can be seen in very ill or hospitalized patients. This may also be called functional hypothyriodism, or subclinical hypothyroidism. However, for the most part a TSH dropping below 1.0 indicates a move towards hyperthyroidism.

The following chart summarizes the varying patterns.

Patters of TSH and thyorid hormone levels

Why TSH is a poor barometer for how severe hypothyroidism is

Often hyperthyroidism patients will look at TSH to see how much better, or worse they are.

However, when we look closely at the relationship between TSH and thyorid hormone it becomes clear that TSH can give very limited information.

The reference range for total T4 (thyroxine) is about 4.5 - 12.5 µg/dL (this may change slightly from lab to lab).

This reference range is far to large. According one person can have nearly 3 times elevated thyroid hormone than another and both are deeded "normal" or healthy. As often the case in conventional medicine, reference ranges are designed to test if someone is sick enough to be treated with drugs or surgery. It can have nothing to do with measuring any marker of optimal health.

So while the reference range is 4.5 - 12.5 means you probably don't need to take any sort of medication (according to conventional medicine), an optimal range may be closer to 5.0 - 7.0. This is just an example, as should not be applied to everyone. Not everyone is necessarily going to have the same optimal range, which can make establishing a universal range for everyone problematic.

The following chart shows how we might expect to see TSH drop, as thyroid hormone increases in a case of hyperthyroidism.

TSH
T4
Symptoms (Chart is only a simple example of a general trends - this is not meant to exactly match expected labs in any real person).
2.0 6.0 none
1.0 6.5 none
0.5 7.0 mild or absent
0.1 8.0 mild or absent
0.1 10 severe
0.1 20 severe
0.1 30 severe  

Notice that with even with very mild elevations of thyroid hormone TSH can drop all the way down to 0.1.

Therefore, while TSH should be monitored, by itself it's a poor way to track progress. Total and free T4 and T3 should be tested as well. This along with carefully monitoring symptoms is the best way to track progress.

If taking a prescription anti-thyroid medication (methimazole or PTU) then TSH, T3 and T4 should be monitied to adjust dose. It's possible for a patient to take too high a dose and actually go hypothyorid.

Hyperthyroidism, Subclinical Hyperthyroidism and Low TSH

An all or nothing diagnosis of either hyperthyroidism, or normal is not sufficient. Using the following 3 catagories is more useful.

Leaning towards hyperthyroidism

Some people have very minor hyperthyroidism. Symptoms may be totally absent, or so mild nothing is thought of it (ie. someoene who feels hotter than others all the time).

Lab tests may be skewed towards hyperthyoidism but still well within reference range. Broadly speaking this will be low normal TSH (about under 1.0) and high normal T4 and/or T3.

Since these patients don't have symptoms bad enough to warrent anti-hyperthyroid drugs such as methimiazole, conventional medicine simply says they are "healthly."

Subclinical hyperthyroidism

This represents "normal" levels of thyroid hormone but a TSH of 0.1. Symptoms may be absent, or very mild.

Realistically, if TSH is 0.1, then thyroid hormone is not optimal (even if in reference range). Reference ranges are very large and are not meant to be a measure of optimal health.

In conventional medicine, doctors may simple monitor patients with subclinical hyperthyroidism to see if it gets better on it's on.

I hightly recommend that this pattern be interpreted as a sign of poor heatlh and preventative meansure using natural health be taken at this point.

Hyperthyroidism

This describes TSH of 0.1, and thyroid hormone above reference range. There are usually many symptoms present.

Free and total T4 / T3

It's best to test both free and total T4 and T3. T4 (thyroxine) is the less active. T3 is the more potent form of thyroid hormone.

Both T4 and T3 may be free or bound. Bound thyroid hormone is attached to a protein (thyroid binding globulin) making it inactive. It doesn't do anything.

Only the free, or unbound thyroid hormone does anything.

Varying ratios of thyroid hormone from patient to patient

In some people with hyperthyroidism, total T3 may be significantly elevated (many times above reference range), but free T3 comparatively low. The ratios between T4, T3, free and total will vary from patient to patient. It's not sufficient to only test a few markers and then make assumptions about the others.

Varying sensitivity to thyroid hormone from patient to patient

IDue to differences in conversion of thyroid hormone to free T3, and sensitivity to thyroid hormone on the cellular level sensitivity to excess thyroid hormone varies greatly from patient to patient.

Some patients many have hyperthyroidism symptoms with thyroid hormone tests well within reference range, and others are mostly symptom free with remarkably elevated thyroid hormone.

It's important to not just test the multiple thyorid hormone markers, but then interpret labs accordingly to each patients' uniuqe presentation.

Future updates:

Sections on thyroid antibodies and RAI-U