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Thyroid UK
91,966 members106,219 posts

Why the variance in fT4 / fT3 ranges in the UK?

I find it crazy that my local fT4 range is 10-19.8, and fT3 is 3.5-5.5, yet about 20 miles away it could be 3.2-6.2 or 9.5-22.3.

We can't all differ that much around the UK, so why is there no UK-wide reference range? I'm still me whether I'm in Glasgow, Cardiff, Belfast or Cambridge!

What are your local reference ranges? It would be interesting to know the variance. And maybe we can use this information to our benefit.

1 Reply

The differences in the reference ranges are caused by the techniques used to measure the concentrations of the various components. Each lab has to calibrate their equipment individually, which leads to slightly different reference ranges. For example, exactly the same blood sample would give a slightly different FT4 reading in every lab testing it.

The reference ranges don't fluctuate *that* much given the inherent inaccuracy in measuring such tiny concentrations of chemicals. And the differences in reference ranges seem pretty much irrelevant in diagnosing overt problems (e.g. when I was diagnosed my FT4 was less than 5 pmol/L, which would be very low on any reference range). But it is a problem when trying to treat borderline or subclinical cases.


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