The truth about thyroid testing is finally told

An article form the National Academy of Hypothyroidism   Copyright ©   2012 about Thyroid Hormone Transport


Thyroid hormone transport is an extremely important topic. It must be clearly understood by any physician who hopes to accurately evaluate an individual’s thyroid status and to appropriately treat thyroid dysfunction. Unfortunately, only a small fraction physicians and endocrinologists understand even the basics of thyroid transport, because what they have learned in medical school and continue to be taught regarding this topic is incorrect. When one understands the physiology involved with thyroid hormone transport, it becomes clear that standard blood tests, including the TSH and T4 levels, cannot be used to accurately determine intracellular and tissue thyroid level in the presence of a wide range of common conditions, including chronic and acute dieting, anxiety, stress, insulin resistance, obesity, diabetes, depression and bipolar disorder, hyperlipidemia (high cholesterol and triglycerides), chronic fatigue syndrome, fibromyalgia, neurodegenerative diseases (Alzheimer’s, Parkinson’s and multiple sclerosis), migraines, cardiomyopathy, and aging.
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“It is clear that serum thyroid hormone and thyroid stimulating hormone concentrations cannot be used with any degree of confidence to classify patients as receiving satisfactory, insufficient, or excessive amounts of thyroxine replacement…The poor diagnostic sensitivity and high false positive rates associated with such measurements render them virtually useless in clinical practice…Further adjustments to the dose should be made according to the patient’s clinical response.” (121)
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In a study published in the British Medical Journal, Meir et al also investigated the correlation of TSH and tissue thyroid effect. It was shown that the TSH level had no correlation with tissue thyroid levels and could not be used to determine a proper or optimal thyroid replacement dose. The authors concluded that “TSH is a poor measure for estimating the clinical and metabolic severity of primary overt thyroid failure. … We found no correlations between the different parameters of target tissues and serum TSH.” They stated that signs and symptoms of thyroid effect and not the TSH should be used to determine the proper replacement dose (122).
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In a study published in the Journal of Clinical Endocrinology and Metabolism, Zulewski et al also investigated the accuracy of TSH to determine proper thyroid replacement. The study found that the TSH was not a useful measure of optimal or proper thyroid replacement, as there was no correlation between the TSH and tissue thyroid levels. Serum T4 and T3 levels had some correlation, with T3 being a better indictor than T4. In contrast, a clinical score that involved a thorough assessment of signs and symptoms of hypothyroidism was shown to be the most accurate method to determine proper replacement dosing. The authors also agreed that it is improper to use the TSH as the major determinant of the proper or optimal doses of thyroid replacement, stating “The ultimate test of whether a patient is experiencing the effects of too much or too little thyroid hormone is not the measurement of hormone concentration in the blood but the effect of thyroid hormones on the peripheral tissues [symptoms] (124).”
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From The Journal of Clinical Endocrinology & Metabolism 2005; 90(12):6403–6409
This study showed that increased T4 and RT3 levels and decreased T3 levels are associated with hypothyroidism at the tissue level with diminished physicial func­tioning and the presence of a catabolic state (breakdown of the body). This study adds to the mounting evidence that giving T4 preparations such as Synthroid and Levoxyl are inadequate for restoring tissue euthyroidism and that a normal TSH cannot be relied upon as as an indication of euthyroidism, as it has a very low sensitivity and specificity for hypothyroidism. This poor sensitivity and specificity is further decreased with the presence of one or more systemic illnesses, including diabetes, heart disease, hypertension, systemic inflammation, asthma, CFS, fibro­myalgia, rheumatoid arthritis, lupus, insulin resistance, obesity, chronic stress and almost any other systemic illness. 
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