In a suprise announcement a prominent leader in the field of thyroid disease, Dr. Leonard Wartofsky, suggested that a new lower level of TSH be utilized when attempting to evaluate and treat hypothyroidism.
When diagnosing hypothyroidism (low thyroid function) most physicians are trained to obtain a TSH measurement. TSH (thyroid stimulating hormone) is produced by the pituitary gland not the thyroid. The pituitary’s job is to act like a thermostat regulating the amount of thyroid hormone in the blood. When the pituitary senses thyroid hormone deficiency this “master gland” releases TSH into the blood to stimulate the thyroid to make more thyroid hormone. TSH therefore increases when thyroid hormone levels are low.
According to good medical training, it is appropriate to diagnose hypothyroidism and give thyroid hormone replacement only if the TSH level is above normal. The normal TSH level is generally recognized to be between 0.4 up to 4 or 5 (microIU/ml) depending on the lab where the assay is done.
I have found that relying strictly on the normal TSH range may fail to render a correct diagnosis of hypothyroidism. Take the situation in which an individual’s TSH level a year ago was 1.0 but this year is 2.8. Both of these TSH levels are within the normal range. Hasn’t something changed, however? Why is the pituitary releasing more TSH this year? My thought is in this situation the pituitary is sensing thyroid hormone deficiency and is trying to compensate by releasing more TSH. In such a case it may be appropriate to try thyroid hormone supplementation if there are also complaints compatible with low thyroid function.
The major flaw in the TSH measurement stategy is to fail to recognize how much variation in thyroid function can be hidden within the TSH normal range. To explain this I like to use the analogy of shoe sizes (you heard it here first!). It is common knowledge that although most people have normal foot size, only one shoe size is appropriate for each person. Similarly with TSH, for each individual there is very likely to be a particular level that is the “best fit”. Recall the normal TSH range is between 0.4 and 4.5. This is equivalent to a normal range of shoe size from 4 to 45! How difficult is it then to find the “best fit”?
For years, endocrinologists have debated what level of TSH is appropriate for the diagnosis of hypothyroidism. In a suprise announcement Dr. Wartofsky from Washington Hospital Center suggested lowering the upper limit of TSH to 2.5 (microIU/ml). This was after an analysis showed that 97% of the population had TSH levels below 2.5. In comparison the official American Association of Clinical Endocrinologists (AACE) statement recognizes the upper normal limit as 5.0, although dissenting members of this organization have been using 3.0 as the upper limit. By recognizing that a TSH level of 2.5 may signify thyroid hormone deficiency, Dr. Wartofsky and his colleagues legitimatize treatment with thyroid hormone replacement for a much broader range of patients then ever before. Public action groups have for years been seeking this reform in the medical community’s method for diagnosing and treating thyroid hormone deficiency.
My comments are intended as informational only, not to diagnose and treat medical conditions. Consult your own physician for individual advice on diagnosis and treatment of medical conditions.
Gary Pepper, M.D. Editor-in-Chief, metabolism.com
