This is a truly important piece of research.
The FT4 and FT3 ranges for individual people are less than half as wide as the large laboratory test population ranges. The research suggests that individual person lab ranges are more like 38% as wide as the laboratory ranges for FT4 and FT3 that endocrinologists and doctors are using to determine if thyroid treatment is correct.
Simply having FT4 and FT3 levels in range according to the lab test result is absolutely no guarantee of thyroid patients feeling well.
I sometimes say, “The laboratory test ranges for FT4 and FT3 are the size of a barn door! Simply throwing a ball and hitting the barn door anywhere at all is not hitting the target. You need to throw the ball a hit within the circle drawn on the barn door. That circle is likely to be around about 38% the size of the total barn door – less than half as wide. If you do not hit within the circle, you have missed your target!”
Here is the article:
“Narrow Individual Variations in Serum T4 and T3 in Normal Subjects: A Clue to the Understanding of Subclinical Thyroid Disease”
Stig Andersen, Klaus Michael Pedersen, Niels Henrik Bruun, Peter Laurberg.
The Journal of Clinical Endocrinology & Metabolism, Volume 87, Issue 3, 1 March 2002, Pages 1068–1072.
See:
https://doi.org/10.1210/jcem.87.3.8165
and (just in case one link breaks at some point):
https://academic.oup.com/jcem/article/87/3/1068/2846746
You also have to be aware of what Normal Ranges actually are. Normal refers to the statistical distribution. This is a technical term, sometimes referred to as ‘Normal’, sometimes as ‘Gaussian’ and sometimes as a ‘Bell Curve’. It means that the shape of the results from a large population fit this particular distribution.
What it DOES NOT mean is that if you have a result that falls within it then you are Normal or Healthy – that is entirely the Wrong Conclusion. Sadly, many doctors and endocrinologists appear to either have forgotten this or did not know it to begin with.
This research paper explains that the ‘normal range’ is Not a range, and being just somewhere in this range does not mean you are Normal:
ncbi.nlm.nih.gov/pmc/articles/PMC6352401
Best wishes,
Paul
