Updated July 30, 2015.

One of the leading experts on hormonal health, Kent Holtorf, MD, has shared his thoughts with me about what constitutes optimal treatment for hypothyroidism, this series featuring practitioners with expertise in hormone balance and hypothyroidism diagnosis and treatment.

According to Dr. Holtorf, optimal thyroid care starts with a proper diagnosis, and continues with supplementation with the optimal thyroid medications at the right dosage to achieve optimal intracellular thyroid activity.

Dr. Holtorf feels that while levels and values of various tests certainly help to determine the most optimal treatment or dose, testing is very prone to inaccuracies under a wide range of conditions. He does not, therefore, rely on or use standard thyroid testing as a sole target to achieve optimal replacement in a large percentage of patients, as he has found that different serum levels may be needed in a particular patient.

For Dr. Holtorf, optimal treatment requires an understanding the complexities of thyroid function. Thyroid function has been oversimplified in an attempt to be able to use a simple test (i.e. the TSH) to define "normal" thyroid levels. According to Dr. Holtorf, this simplistic view breaks down when one understands the many steps that are required to achieve optimal tissue thyroid activity.

Says Dr. Holtorf:

The standard tests will, in general, only detect dysfunction when the thyroid gland is the source of the problem. While primary hypothyroidism (when the thyroid gland is the source of the dysfunction) is the most commonly diagnosed, other causes of sub-optimal or low tissue thyroid activity are much more common but only rarely diagnosed. These other causes include:

• dysfunction of the hypothalamus and pituitary
• impaired cellular transport
• poor T4 to T3 conversion,
• increased formation of reverse T3
• thyroid receptor blockage
• inhibition of thyroid stimulated gene activation.

If there is a problem in any one of these steps, there will be suboptimal or low tissue thyroid activity that usually goes undetected.

Dr. Holtorf believes that once the many potential sources of thyroid dysfunction are understood, laboratory tests -- in conjunction with symptoms and other physiologic signs -- can be more effectively used as tools to help determine optimal treatment.

Dr. Holtorf offers an example:

If there is a dysfunction at the level of the receptor or gene activation, which occurs to varying degrees with chronic illness, inflammation, depression, exposure to plastics such as bisphenol A (BPA), chronic infections, obesity and diabetes, supraphysiologic serum levels of T3 would be needed to overcome this inhibition. In such cases, standard serum thyroid tests become less reliable so other tests must be utilized to best determine optimal tissue thyroid activity. These may include a sex hormone binding globulin (SHBG) level, tendon reflex relaxation speed and basal metabolic rate. These tests should all be interpreted in conjunction an evaluation of signs and symptoms, which are, of course, a very important means of determining optimal treatment.

Tests to Aid in Assessment of Optimal Thyroid Replacement

Dr. Holtorf has a number of tests that he feels are useful in helping to assess optimal thyroid replacement.

TSH—Dr. Holtof considers a TSH above 2 as clear indication that there is low tissue thyroid levels. Says Dr. Holtorf: "A normal TSH does not rule out thyroid dysfunction and a low TSH is shown to be an indication of excessive tissue thyroid levels only 20% of the time (80% of the time that is not the case). The TSH becomes an extremely poor marker for tissue thyroid levels if there is any inflammation, depression, chronic illness, chronic dieting, obesity, stress, chronic fatigue syndrome, fibromyalgia, diabetes, insulin resistance, leptin resistance present."

T4--Dr. Holtof feels that with T4, if there is a problem with thyroid hormone transport (T4 and T3 being transported into the cell), high T4 levels may be associated with lower cellular levels of thyroid.

Free T3-- Dr. Holtorf believes that in general, the free T3 should be in the upper 25th percentile of the normal range. Says Dr. Holtorf: "The 'normal; range is, however, applicable when prescribing T4, which is converted to T3 in the cell and then the amount that leaks back into the serum is the "normal" level. When treating with T3, this is not the case so standard reference ranges cannot be used."

Reverse T3—According to Dr. Holtorf, Reverse T3 is both a marker for reduced T4 to T3 conversion and for reduced transport of T4 into the cell -- and has antithyroid activity (blocks the effect of thyroid) -- and should be less than 150.

SHBG—Sex hormone binding globulin (SHBG) is a marker for tissue level of thyroid, so if less than 70 in a woman, Dr. Holtorf considers it a marker for low or suboptimal tissue thyroid activity. If thyroid replacement is given and SHBG does not increase proportionally, he feels this is an indication of thyroid resistance.

Leptin—Dr. Holtof believes that the serum leptin level should be less than 12. The higher the leptin level, the greater the leptin resistance, which suppresses TSH production and T4 to T3 conversion. Thus, the higher the leptin the more useless the TSH becomes.

Iron/Iodine —Dr. Holtorf also believes that iron and iodine levels should be checked and deficiencies should be treated, as they are required for thyroid activation.

Basal Metabolic Rate (BMR)—Dr. Holtorf finds that tissue thyroid levels are a major determinant of overall metabolism so the overall metabolic level can be considered the gold standard for the body's thyroid level. Thus, the BMR can be used to help determine the most optimal level. This is test that can done in some doctors' offices.

Relaxation Phase of Tendon Reflex—According to Dr. Holtorf, numerous studies have shown that this is a more accurate measure than serum blood tests, as it is more of a measure of tissue activity, rather than serum levels, and the optimal level should be faster than 110 msec.

Kent Holtorf, MD is the founder of the Holtorf Medical Group, which specializes in treating complex endocrine, hormonal and other illnesses in California's Bay Area and the Los Angeles region.

Holtorf Medical group website: www.holtorfmed.com

_{Source: Email interview with Kent Holtorf, MD - December 2010}