When physicians review a patients blood test results, their primary concern is any result that falls outside the normal laboratory reference range. The problem is that standard reference ranges usually represent average populations rather than the optimal level required to maintain good health. It now appears that most standard reference ranges are too broad to adequately detect health problems or prescribe appropriate therapy on an individual basis. This is especially true when these reference ranges are relied on to treat a patient with a serious medical disorder.
An example of flawed reference ranges can be seen in blood tests used to assess thyroid status. A long-standing controversy rages over the best way to diagnose thyroid deficiency. Most conventional doctors rely on thyroid blood tests whereas alternative physicians look for signs and symptoms of thyroid deficiency. An article in the August 3, 2002, issue of the British medical journal Lancet challenged conventional medical wisdom regarding the use of standard reference ranges in diagnosing and treating thyroid deficiency. According to the researchers, the problem with thyroid blood tests may be faulty reference ranges that fail to reflect what the optimal level of thyroid hormone should be in a particular individual .
The standard blood test used to determine thyroid gland hormone output is the thyroid-stimulating hormone (TSH) test. When a deficiency in thyroid hormone occurs, the pituitary gland releases TSH to signal the thyroid gland to produce more hormones.
When the TSH level is in the normal range, doctors usually assume that the thyroid gland is secreting enough thyroid hormone. The question raised by the Lancet articles authors, however, was whether the current reference range for TSH reflects optimal thyroid hormone status.
The TSH reference range used by many laboratories is 0.35“5.50 mIU/mL (milli international units per milliliter). A higher TSH level indicates a thyroid hormone deficiency (because the pituitary gland is oversignaling TSH to compensate for low levels of thyroid hormone in the blood). Any reading of more than 5.50 mIU/mL alerts a doctor to a thyroid gland problem and the possibility that thyroid hormone therapy may be warranted.
The trouble is that the TSH reference range is so broad that most doctors will interpret a TSH reading as low as 0.35 to be as normal as a 5.50 reading. The difference between 0.35 and 5.50, however, is 15.7-fold, a range of values far too great to indicate optimal or even normal thyroid function.
A review of published findings about TSH levels reveals that readings greater than 2.0 may indicate health problems relating to insufficient thyroid hormone output. One study showed that individuals with TSH values greater than 2.0 have an increased risk of developing clinically significant thyroid deficiency during the next 20 years . Other studies show that TSH values greater than 1.9 indicate risk of autoimmune disease of the thyroid gland .
A more startling study showed that TSH values greater than 4.0 increases the likelihood of heart disease in postmenopausal women . Another study showed that administration of thyroid hormone lowered cholesterol in patients with TSH ranges of 2.0“4.0 but had no cholesterol-lowering effect in patients whose TSH value was in the 0.2“1.9 range . It also showed that in people with elevated cholesterol, TSH values of 2.0 or greater could indicate that a thyroid deficiency is the culprit, causing excess production of cholesterol, whereas TSH levels at or below 1.99 would indicate normal thyroid hormone status.
Doctors routinely prescribe cholesterol-lowering drugs to patients without properly evaluating their thyroid status. Based on the evidence presented to date, it might make sense for doctors to investigate a thyroid deficiency (based on a TSH value greater than 1.9) before resorting to cholesterol-lowering drugs.
In a study to evaluate psychological well-being, impairment was found in patients with thyroid abnormalities who were nonetheless within normal TSH reference ranges .
The authors of the Lancet study stated, The emerging epidemiological data begin to suggest that TSH concentrations above 2.0 (mU/L “ milliunit per liter) may be associated with adverse effects.
The authors prepared a chart based on previously published studies that provides guidance when interpreting the results from TSH blood tests. Here are three highlights from their chart that may be useful in understanding what your TSH values really mean:
TSH values greater than 2.0: increased 20-year risk of thyroid deficiency and increased risk of thyroid-induced autoimmune attack 
TSH values greater than 4.0: greater risk of heart disease 
TSH values between 2.0 and 4.0: cholesterol levels decline in response to thyroxine (T4) therapy 
Despite these intriguing findings, the Lancet authors stated that more studies were needed to define an optimal TSH range, suggested as 0.2“2.0 instead of 0.2“5.5 (mU/L). Note: These optimal reference ranges are now expressed in mIU/mL, so the ideal range according to this epidemiological data is 0.35“2.1 mIU/mL.
If you have depression, heart disease, high cholesterol, chronic fatigue, poor mental performance, or any of the many other symptoms associated with thyroid deficiency, you may want to ask your doctor to defy the reference ranges and try a different thyroid replacement therapy.
- (Dayan CM et al 2002)
- (Vanderpump MP et al 1995)
- (Hak AE et al 2000)
- (Michalopoulou G et al 1998)
- (Pollock MA et al 2001)
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