Saturday, November 14, 2009

Hypothyroidism and the Limitations of Blood Tests

Hypothyroidism is an important condition to recognize and properly treat. Some diseases associated with hypothyroidism include:

· Coronary artery disease
· Congestive heart failure
· Chronic fatigue
· Depression
· Memory problems
· Fibromyalgia – painful muscles
· Attention deficit
· Chronic or recurrent infections
· Fertility problems
· Menstrual irregularities

Medical Dogma & The Tyranny of the TSH
Since hypothyroidism causes so much suffering, disease and death, we must do everything possible to properly identify those who need treatment. Sadly, it appears that the medical community has actually taken many steps backward in their approach to hypothyroidism.

If you saw a doctor in 1960 and you had hypothyroidism, you would have been diagnosed based on your symptoms and physical exam findings and treated with natural thyroid. You would have improved and enjoyed good health. Today you would typically not be so fortunate.

Since the 1970’s doctors have been actually trained to ignore symptoms and signs of hypothyroidism unless they see an elevated pituitary hormone called the Thyroid Stimulating Hormone (TSH). If the TSH is elevated doctors are taught to treat using L-Thyroxine (aka T4). The TSH was adopted as the standard for diagnosing hypothyroidism by a consensus opinion in 1973. This decision was made on the basis of “expert opinion” and consensus rather than actual studies which show that using the TSH is the best way to approach hypothyroidism. The advocates of the TSH standard felt that it provided a more objective means of determining thyroid status than clinical parameters and after more than 30 years the TSH Approach has become medical dogma. The assumption that it is the right thing to do appears to be validated by the fact that so many physicians are doing it. Could we be missing something?

Does the TSH Approach Work?

Yes and No. The TSH is an excellent indicator of severe underproduction of thyroid hormone. A high TSH is typically present when the production of thyroid hormone is dramatically lowered such as when the thyroid gland is removed. The regulation system detects a low level of thyroid hormone and attempts to get the levels back to normal by making an excessive amount of TSH in a vain attempt to get the thyroid gland to produce more.

While a high TSH does indicate the underproduction of thyroid, a TSH level within the reference range does not assure optimal thyroid status. Why? Hypothyroidism is low thyroid function within our cells. No blood test can directly measure the thyroid activity within the cells of our body.

Why would a cell have sluggish thyroid function?

A. Underproduction – the thyroid gland produces too little thyroid

B. Cellular Underutilization – thyroid hormone only does it job within the cells of our body. Numerous steps are involved in thyroid hormones effect to help the cells produce and use energy. The cell will function sluggishly if the thyroid hormone is not used efficiently

C. A Combination of A and B

One should realize that for the medical community to use the TSH as the sole basis for diagnosing hypothyroidism one must make several huge assumptions that are not typically discussed in textbooks or lectures. The majority of the medical community has adopted a model which knowingly or not has assumed the following to be true:

1) The central regulation mechanisms in the hypothalamus and pituitary gland are assumed to be working perfectly. The thermostat like set point for serum thyroid levels within our brain is assumed to function perfectly – unaffected by aging, stress, nutritional deficiencies, toxins or genetic factors.

2) Perfect utilization of thyroid at the cellular level is assumed. Once again this assumes that the delicate process of utilizing thyroid is unaffected by aging, stress, nutritional deficiencies, toxins or genetic factors.

3) “Anywhere in the range” is fine for an individual. The model that doctors typically use assumes that individuals are perfectly fine if they are anywhere within the reference range.

Is assumption #1 true? Do central regulatory mechanisms work perfectly?
No. Consider the following quote made in the respected Primary Care Clinics:

“With significant physiologic stress, illness, inflammation and aging, however, there is demonstrable suppression of thyrotropin, making the thyrotropin test unreliable”

Primary Care: Clinics in Office Practice Volume 35, Issue 4, (Dec 2008) 669–705

Is assumption #2 true? Is thyroid hormone perfectly used in our cells at all times?
No. Hormone resistance is common

Our new understanding of endocrine dysfunction suggests that hormone resistance is more common that previously recognized. Consider both leptin and insulin.

- Underproduction is uncommon: Underproduction of leptin is rare and underproduction of insulin constitutes less than ten percent of all diabetes

- Cellular underutilization of hormones is common: leptin is almost universal with obesity and most with type 2 Diabetes have high insulin levels associated with their insulin resistance

If leptin and insulin resistance is common, could thyroid resistance be common as well?

We now have strong evidence that the intracellular conversion of thyroxine (T4) to the active form triiodothyronine (T3) is inhibited by numerous common factors. Hypothyroidism related to intracellular factors will not be reflected in changes in either the TSH or free hormone levels. Drs. Boc and Starr have adopted a reference mechanism of Hypothyroidism Type I for underproduction and Hypothyroidism Type 2 for peripheral hypo-utilization (described in the book, Hypothyroidism Type 2, Mark Starr, M.D.).

Cellular resistance can be compared to a factory with enough workers showing up but they are unable to do their job efficiently. The workers are our hormones but the factory is the cell.

We can see how many workers are showing up for work by measuring the hormone level but we cannot see how well they are working inside the factory. To gain a window into the status of our cellular factories we must step back and look at the person who is made up of all those cells. If every cell in our body is sluggish, we will see it reflected in having some of the symptoms of sluggish cell function – tired, cold, dry skin, depressed mood, memory and focus issues, constipation, aches and pains, hair loss. The body temperature may be low.

It is a cellular world

The study of what happens in our cellular factories is more challenging and has only recently been worked out in detail. We now know that cells regulate thyroid function independent of the brain/pituitary regulation system. It is well known that many chronic illnesses produce the so called sick-euthyroid syndrome characterized by normal thyroid labs but decreased thyroid function. This is often seen in many hospitalized patients with serious illnesses. We now know that under stress our cells can slow metabolism of some tissues by increasing the intracellular conversion of T4 to Reverse T3 instead of the active form of thyroid T3.

The cellular regulation of thyroid is not reflected by changes in the serum thyroid levels or the TSH. In fact these changes may only occur in certain organs and not others. During starvation the brain thyroid function continues but less critical function in the muscles and GI tract will be slowed. The TSH remains unchanged while our tissues are adjusting thyroid function to cope with our stressors. Interestingly, those of Irish decent tend to have a higher rate of thyroid underutilization problems (Hypothyroidism Type 2) due to the fact that their ancestors were the ones who survived the great potato famine of 1845 and 1852. Those who more readily slowed their metabolism presumably by producing more reverse T3 would have had a survival advantage. Therefore, descendents of these survivors may be more prone to produce reverse T3 when they encounter stress from any source; however, their TSH levels are unchanged.

Is assumption #3 true? Is the entire reference range of the TSH or thyroid hormone level necessarily that which will be optimal for an individual?
No. The reference range simply describes where most of the population is. This is made up of people of all backgrounds, young and old, healthy and ill. In order for you to have the best possible thyroid status you need to be at your optimal level. For example, when one buys shoes, one is interested in getting a little more specific than getting a “normal” shoe. I have never heard anyone say “just give me any size normal shoe in that style.” In fact most normal shoes are not right for your foot. Similarly, a person with the signs and symptoms of low thyroid and a test result that is at the 50th percentile may feel great at the 60% percentile. Another person may be in the 10th percentile and be perfectly healthy because that is their optimum.

An optimal thyroid status is much more than feeling good. In 2008 the HUNT study showed that women with a higher TSH had a 69% higher rate of heart disease (odd ratio 1.69). This dramatically increased rate of heart disease was found with TSH levels within the reference range. (see Thyrotropin Levels and Risk of Fatal Coronary Heart Disease The HUNT Study Arch Intern Med. 2008;168(8):855-860

Conclusion: When the TSH is used alone to diagnose hypothyroidism, most who suffer from hypothyroidism will be missed. A high TSH typically indicates underproduction of thyroid. A normal TSH can be present in those with severe cellular underutilization of thyroid. This appears to be common and must be addressed. The TSH Standard for hypothyroidism diagnosis and management needs to be revised to reflect our current understanding.

Next issue: What Causes Hypothyroidism and What You can Do About it