Thyroid - the correct prescribing of thyroid hormones
From DoctorMyhill
There are three reasons why UK citizens are not subject to "best practice" with respect to prescribing thyroid hormones. Two of those reasons are biochemical, one reflects drug company influence. All relate to the prescribing of thyroid hormone for underactive thyroid glands (hypothyroidism).
The threshold for thyroid stimulating hormone (TSH) is set too high.
When levels of thyroid hormone in the blood start to fall, the pituitary gland increases its output of thyroid stimulating hormone which kicks the thyroid into life and increases output of thyroid hormones. If the thyroid gland starts to fail, this is reflected by levels of TSH rising. The question is at what point should the prescription of thyroid hormones begin?
The normal range for TSH in this country varies enormously from one laboratory to another. This means in some locations in the UK a thyroid prescription would not be given until the TSH rose above 5.0mlU/l.
As a result of research, the normal range for TSH in America has now been reduced so that anybody with a TSH above 3.0 is now prescribed thyroid hormones. This research has shown that people with a TSH above 3.0 are at increased risk of arterial disease (a major cause of death in Western culture), insulin resistance (and therefore diabetes), inflammation and hypercoagulability (sticky blood). Indeed, there is a recommendation afoot in America to further reduce the threshold for prescribing to 2.5mlU/l.
What is completely illogical is that in UK the target TSH level for patients on thyroid replacement therapy is often stated as being less than 2 or even less than 1.5. This is a ridiculous anachronism and UK physicians should catch up with modern research.
We should reduce the threshold for prescribing thyroid hormones to <3.0mlU/L or better still 2.5mlU/l.
The population normal range for levels of thyroid hormone in the blood is not the same as the individual normal range
We differ as individuals in our biochemistry as we differ in our looks, intelligence and morphology. This biochemical variation should be taken into account when it comes to prescribing thyroid hormones.
The population normal range of a Free T4 is 12 - 24pmol/L. A patient, therefore, with blood levels of 12.1 would be told they were normal because they are within the population reference range. But actually that person's personal normal range may be high. They may feel much better running a high T4 of say 22, i.e. nearly twice as much but still within the population reference range.
Research done originally in UK, and now repeated in America, clearly shows that the individual normal range of thyroid hormones is not the same as the population referrence range. In order to find out who these individuals are, patients have to be assessed clinically as well as biochemically. In actual UK clinical practice this is rarely done except by a few physicians conversant with this issue.
Some people feel better on different preparations of thyroxine
In theory, if the patient has been shown to be hypothyroid then all their symptoms should be improved with synthetic sodium thyroxine. In practice, this is not always the case - there is no doubt that clinically some patients feel very much better taking biologically identical hormones such as natural thyroid (a dried extract of pig thyroid gland which is a mix of T4 and T3). Indeed before synthetic thyroid hormones became available, all patients were routinely treated with natural thyroid. The purity and stability of these preparations has been long established, indeed much longer than synthetic thyroxine!
Part of the reason why people fell better taking natural bio-identical hormones is that some people are not good at converting T4 (which is relatively inactive) to T3 (which is biologically active). However this does not explain the improvement in every case. It is difficult to explain why there should be an additional effect, but for many people it is the difference between drinking cheap French plonk and good quality Spanish Rioja. The alcohol content is the same, but the experience completely different!
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Thyroid profile: free T3, free T4 and TSH
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References
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