NICE thyroid reference ranges

[bobbobing]

I just wondered if anyone knows if the NICE thyroid reference ranges changed for their new guidance. Did they adjust for different age groups or anything? It is strange that normal range for TSH is up to around 5 but don't treat till at 10.

[helvella Administrator Thyroid UK]

Nothing to do with a NICE reference range. They did as so many do, quote research with various TSH ranges, then write as if all ranges were the same. But that only meant effectively ignoring minor differences like 0.35 to 4.5 rather than 0.25 to 4.1, 0.40 to 4.6.

The "don't treat until 10.0" is simply a nonsense which is invalid.

I suspect the underlying idea is to avoid treating people who have only very slightly low thyroid hormone levels. (Sometimes people have a period of being slightly hypothyroid and then simply get better.)

There are lots of reasons to think this is wrong-headed.

In my own case, I could see TSH rising over many months, a little each time. The direction (up!) was consistent and obvious. And when I got treated I had numerous symptoms - albeit mostly towards the mild end of the scale. I cannot see any benefit, certainly to the individual patient, of leaving them for what might be a very long time, before treating. They will only deteriorate. Issues which might be mild will worse. Issues which might be temporary will tend to become permanent.

It is my opinion that in many of us, the amount of TSH we can produce is limited. The longer we have an elevated TSH, the more TSH we tend to be able to produce. Therefore, a higher TSH is the product of being hypothyroid for a long time rather than being more hypothyroid. And, without Free T4 and Free T3, you really cannot know what is going on. Any decision based only on TSH is unscientific and illogical.

My TSH rose just about range. My Free T4, when eventually tested, was right at the very bottom of the range. I had many symptoms. But, more than anything else, I was lucky my GP accepted and prescribed levothyroxine for me.

[jimh111]

TSH can be very useful for diagnosing primary hypothyroidism, a failing thyroid. The cutoff of 10.0 is used because that is where the balance changes, with a TSH less than 10.0 the patient is unlikely to have primary hypothyroidism.

Unfortunately, doctors fail to recognise other forms of hypothyroidism and so these are missed. For example, TSH secretion may be below par leading to reduced thyroidal secretion and reduced deiodinase.

Trying to lower the diagnostic TSH threshold is counterproductive, a doctor could quite reasonably argue that your TSH is now 2.0 so you must be fine.

We need to focus less on TSH and more on signs and symptoms so that all forms of hypothyroidism are recognised and treated appropriately.

[helvella Administrator Thyroid UK in reply to jimh111]

The cutoff of 10.0 is used because that is where the balance changes, with a TSH less than 10.0 the patient is unlikely to have primary hypothyroidism.

I cannot see why a TSH of, say, 4.6 (reference interval goes up to 4.5) says a patient is unlikely to have primary hypothyroidism. At least, not such that a decision not to treat can be based on that alone.

Everyone who progresses from euthyroid to hypothyroid will go through 4.6. It is a matter of timing - if tested at that point...

Even if 90% of patients with a TSH of 4.6 do not have primary hypothyroidism, 10% do!

If suddenly at a TSH of 10.0 99% of patients do have primary hypothyroidism, some don't.

A magic TSH number is not adequate for determining whether or not a patient has primary hypothyroidism.

It is, yet again, applying population statistics to individuals.

I tend to look at it as a second bite of the "don't treat" cherry. It is well known that few without any thyroid issue have a TSH even as high as 2.5. So there is a gap between 2.5 and 4.5 to allow "let's see how it goes" and monitor (and measure FT4!). Then they add from 4.6 to 10.0 as well. Further, we have even seen some patients told that they are only just over 10 so no diagnosis, no prescription.

[jimh111 in reply to helvella]

The cutoff at 10.0 is supplemented by checking fT4 also. This is just guidance, doctors are supposed to use their judgement also but alas this is happening less and less.

For patients who are hypothyroid with a TSH of e.g. 4.6 it is most unlikely it is due to primary hypothryoidism (insufficient hormone from the thyroid). If it were, just a little levothyroxine would bring their TSH down to 1 or 2 and they would be hunky-dory. This rarely happens. Their problem is not due to insufficient hormone.

Pushing for a lower TSH diagnostic cut-off is a bad strategy: -

1. It reinforces the concept that TSH is always definitive.

2. It denies the fact that patieints can be hypothyroid with a perfect TSH.

3. It fails to recognise that primary (and rarely secondary) hypothyroidism are not the only causes of hypothyroidism.

4. The wrong diagnosis is made. Time and effort is wasted on the wrong approach and the patient may never receive appropriate therapy.

Patients are hypothyroid with TSH < 10.0 but it is most likely due to other causes than simply an under-performing thyroid. This is important because the evidence quoted to NICE etc. only considers primary hypothyroidism. Thus, the evidence does not apply to hypothyroidism in general.

[bobbobing in reply to jimh111]

So what other causes are there?

[jimh111 in reply to bobbobing]

I can list two I have encountered! See the links in my profile.

1. Endocrine disruption. A number of chemicals introduced from the 1970s have an almost identical structure to T3 and are able to disrupt the action of T3. Ironically, these tend to disrupt T3 action in peripheral tissues but not in the hypothalamus / pituitary. The patient can be severely hypothyroid with normal thyroid hormone levles.

2. Subnormal TSH secretion. If a patient has a period of high hormone levels (as can happen in autoimmune hypothyroidism) their 'axis' can be down-regulated, their pituitary secretes less TSH than expected. This is a form of mild central hypothyroidism. I needed very high doses of thyroid hormone for a decade to overcome my endocrine disruption, this down-regulated my axis, my TSH is much lower than it used to be for given fT3, fT4 levels. Subnormal TSH secretion not only leads to insufficient stimulation of the thyroid it also reduces T4 to T3 conversion. I see lots of these cases on the forum, here is a current one healthunlocked.com/thyroidu... .

I'm sure there are other causes of hypothyroidism. We need to persuade doctors to diagnose using signs and symptoms, using the blood tests to give a clue to the underlying cause. If we don't identify the cause we can't get the right therapy or judge the risks of under or over treatment.

[helvella Administrator Thyroid UK in reply to bobbobing]

Having antibodies to TSH itself.

If you have them, those antibodies attach to TSH to form a complex called macro-TSH.

That will often show as a somewhat raised TSH - but it depends on which assay kit is used - some are immune to macro-TSH; others are not.

[SlowDragon Administrator in reply to bobbobing]

Other causes of low TSH

Low vitamins

Hashimoto’s....levels can swing so much that TSH can’t keep up

Dio2 gene variation...very common with many Hashimoto’s patients

Drug induced hypothyroidism, often overlooked by medics

ncbi.nlm.nih.gov/pmc/articl...

[Angel_of_the_North]

There are no NICE references ranges. Reference ranges are set by the lab according to the equipment used and (often) local population. You need to use the range given with your test results.

[tattybogle in reply to Angel_of_the_North]

For Example:- TSH ranges, using same lab in NW England over time:-

2003 [0.36-4.1]

2005 [0.02-6]

2015 [0.05-6]

2016 [0.34-5.6]

2018 [0.57-3.6]

Note: many people have a poor opinion of the quality of the research (on machines and local population) done to achieve these ranges.

[SlowDragon Administrator]

NICE have clearly stated it’s important to increase levothyroxine to full replacement dose using guidelines to dose by weight

Can be helpful when pushing for dose increase

Even if we don’t start on full replacement dose, most people need to increase dose slowly upwards in 25mcg steps (retesting 6-8 weeks after each increase) until on full replacement dose

NICE guidelines on full replacement dose

nice.org.uk/guidance/ng145/...

1.3.6

Consider starting levothyroxine at a dosage of 1.6 micrograms per kilogram of body weight per day (rounded to the nearest 25 micrograms) for adults under 65 with primary hypothyroidism and no history of cardiovascular disease.

BMJ also clear on dose required

bmj.com/content/368/j

healthunlocked.com/thyroidu....