What is happening here? Many doctors rely only on TSH marker to diagnose and manage thyroid disease; however, this is just one of the four needed markers to establish a correct interpretation and analysis of your thyroid status. Moreover, many doctors use the lab ranges (referred to as "pathological" or disease ranges) that come with the test results, instead of functional ranges, which have been carefully researched and formulated as parameters of good thyroid health.
The lab ranges are simply the averages of all the people who have had blood work analyzed by that lab in the last year. They are so called "normal" or "healthy" places to be but are actually statistical averages. Different labs can and do have different reference ranges. It is common to have a test result come back "normal" from one lab and "out of range" for another lab. In truth, if your lab values are within the set reference range, you are within the "average" and not necessarily healthy.
Each lab director sets the reference range for each particular test based upon a percentage of people who have taken the test. Essentially, laboratories are relying upon a bell curve to determine each reference range. The standard in medicine is to establish the mean and then set two deviations, one above and one below the mean. These reference ranges will continue to get wider and wider, as patients get sicker and sicker.
Like all endocrine glands, the thyroid does not exist independently of other glands. The thyroid is a part of the HPT axis (hypothalamus, pituitary, thyroid) and as such is under the influence of several hormones and feedback loops. Additionally, the thyroid is intrinsically linked to the adrenal glands and can be greatly affected by the body's responses to stress.
As an example of this, it is well established that increased levels of glucocorticoid hormones such as cortisol, can inhibit TSH release by the anterior pituitary, as well as the conversion of T4 into T3, which takes place in the liver.
What Are the Necessary Markers to Correctly Assess Thyroid Function and Thyroid Testing?
Many endocrinologists consider measuring TSH levels to be the "gold standard", but other markers are as important to be carefully analyzed, like Free T4, and Free T3 (the actual circulating thyroid hormones) or antibodies like TPO (thyroid peroxidase antibodies) to detect autoimmune thyroid disease. If you don't test these markers also, you can run the risk of having sub-normal levels of T4 and T3, and/or antibodies that show that your thyroid gland is in self-destruct mode. Frustrating as it may sound, if TSH is within the reference range, the endocrinologist may say your thyroid functions "normal"
TSH (Thyroid Stimulation Hormone) is the most common marker of thyroid function. It is a hormone released by the pituitary gland and directly signals to the thyroid gland to produce T4 (thyroxine). TSH secretion is stimulated by the hypothalamic hormone TRH (thyroid releasing hormone). Negative feedback mechanisms within the HPT axis (hypothalamic/pituitary/thyroid) further regulate TSH secretions. An elevation in TSH is one indicator of decreased thyroid activity. TSH increases when T4 drops and decreases when T4 rises.
TSH levels above 2.5 are considered to be suspicious for subclinical hypothyroidism by many integrative physicians.
Free T4 (Free Thyroxine) is used to measure the amount of free (active) T4 in the blood. It is high with hyperthyroidism and low with hypothyroidism. The Free T4 test measures the available amount of the T4 storage hormone available to be converted into T3, the active thyroid hormone.
While the reference range at many labs runs from .8 to 2.8 ng/dL, integrative physicians have found that most patients feel best when their level falls into the top half of the range, at a level of 1.3 or higher.
Free T3 (Free Triiodothyroxine) measures free T3 hormone and is the best marker for measuring active thyroid hormones available to thyroid receptor sites. Free T3 measures are more clinically relevant than Total T3 measures. Decreased FT3 measures are one indicator of low thyroid activity.
While the reference range at many labs runs from 2.3 to 4.2 pg/mL, integrative physicians have found that most patients feel best when their level falls into the top half of the range, at a level of 3.2 or higher, and in many cases, at 3.7 or higher.
Reverse T3 is a measure of the amount of T4 that is converted into a biologically inactive form of the T3 hormone. Integrative physicians have found that elevated levels of Reverse T3 may suggest that thyroid hormone is not properly converted from T4 into T3, for use by the cells, and may result in hypothyroidism symptoms despite otherwise "normal" levels of Free T4, Free T3 and/or TSH.
A combination of the serum levels of TSH, free T3, free T4, reverse T3, and anti-TPO antibody, antithyroglobulin antibody and SHBG should be used in combination with clinical assessments and measurements to most accurately determine the overall thyroid status in a patient.
Forgoing treatment based on a normal TSH without further assessment will result in the misdiagnosis of a large number of hypothyroid patients that may greatly benefit with treatment. Simply relying on TSH to determine the thyroid status of a patient demonstrates a lack of understanding of thyroid physiology and is not evidence based medicine.
