Further on Roche assays

[AKatieD]

After discovering that most of us will be tested using a Roche assay system and that they can give higher results than other systems, I have kept looking....

A different, very interesting Medscape study popped up this week (albeit from 2005) based on Roche assays:

academia.edu/128071385/New_....

It says that, the reference ranges (especially for T3) should be different for men/ women, different ages and whether on oral contraceptives or not. Women on OC had higher top Free t3 range (over 7 compared to top of standard at 6.8), more than any other group. I infer this means HRT will affect reference ranges and not just oral contraceptives. They also found the standard reference range for TSH not right at either end.

It also says whilst the recommendation is for each lab to work out their own reference range ( using healthy men under 30!), few do and mostly just use the assay manufacturers recommendation as it is easier!

They looked at those that were without personal history of thyroid problems (whole group) and a constrained group (excluded those with family history, raised antibodies or abnormal thyroid ultrasound, taking meds other than oral contraceptives).

I guess unsurprisingly, they had to exclude almost a half for having thyroid problems when they thought they were completely healthy. Apparently, reference range studies don't usually do this! Even more unsurprisingly 77% showed normal TSH but not normal thyroids on ultrasound.

[helvella]

Around that time we actually saw a change in TSH reference intervals.

From memory alone, and using approximate figures, we used to see the top of TSH ranges in the UK was typically around 7 or even higher. The USA often had slightly lower tops of TSH ranges.

After the research you quote (and other papers with similar observations), we first saw lots of USA TSH ranges drop the tops of ranges. With UK ranges following - sometimes years later.

A smaller percentage of USA labs continued to use TSH ranges out of step with the rest of the country for many years. I suspect we should be asking who was in change of the labs? It could have been ignorance and/or unwillingness to pay to re-establish ranges.

The failure to exclude those with identifiable thyroid issues was an appalling misjudgement. Wholly dumb.

[asiatic]

And just to add to the general confusion the following paper suggests caution should be used at levels close to cut offs due to inconsistencies.

How low can we (reliably) go? A method comparison of TSH assays with focus on low concentrations

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

[AKatieD in reply to asiatic]

Yes, results at either end if range are unreliable

[tattybogle]

healthunlocked.com/thyroidu.... difference-in-reference-ranges-reading-matter-for-a-rainy-day-.