Variable effects of nonsteroidal antiinflammatory agents on thyroid test results

[helvella]

Three things came together. First, reading through some of diogenes' papers, second, noticing the old PR Larsen paper, third, that someone expressly mentioned taking aspirin in order to help with blood flow when performing a finger-prick blood sample. (I did try, but I could not find where on the forum it was mentioned!)

The effect of aspirin and other salicylates is definitely at the level which could affect blood test results. Therefore using it prior to a thyroid hormone test (TSH, T4 or T3) is probably a bad idea.

It isn't quite as clear whether there is sufficient reason to avoid aspirin entirely in all those with thyroid issues. I suspect that it is possibly safest to avoid. In particular, in someone who is significantly hyperthyroid - when the unbinding of more thyroid hormone could cause their free hormone levels to rise even further.

Variable effects of nonsteroidal antiinflammatory agents on thyroid test results.

Abstract

To investigate the effects of nonsteroidal antiinflammatory drugs (NSAIDs) on thyroid tests, 25 healthy subjects underwent a single-dose study and/or a 1-wk study. In the single-dose study, subjects received a single dose of one of six NSAIDs (aspirin, salsalate, meclofenamate, ibuprofen, naproxen, or indomethacin) at 0800 h. Total and free thyroid hormones and TSH were analyzed 0, 1, 2, 3, 4, and 8 h later. In the 1-wk study, subjects received one of six NSAIDs for 7 d. Thyroid hormones and TSH were analyzed at 0800 h each day. Total T(4) and total T(3) were measured by RIA, free T(4) and free T(3) were measured by equilibrium dialysis, and TSH was measured by immunometric assay. There were no changes in any hormones after a single dose or 1 wk of ibuprofen, naproxen, or indomethacin. Single-dose aspirin or salsalate decreased, whereas meclofenamate increased, various total and free thyroid hormone measurements. One week of aspirin or salsalate decreased total T(4), free T(4) (salsalate only), total T(3), free T(3), and TSH. These data confirm that aspirin, salsalate, and meclofenamate affect total and free thyroid hormone measurements and identify three NSAIDs that did not change thyroid tests. TSH remained within the normal range during acute or 1-wk administration of all of the NSAIDs.

Abstract only access:

europepmc.org/article/MED/1...

This is an old paper - but every subsequent work seems to reference it!

Salicylate-induced increases in free triiodothyronine in human serum. Evidence of inhibition of triiodothyronine binding to thyroxine-binding globulin and thyroxine-binding prealbumin.

Larsen PR

The Journal of Clinical Investigation, 01 May 1972, 51(5):1125-1134

doi.org/10.1172/jci106905 PMID: 4623165 PMCID: PMC292242

Free full text in Europe PMC

Abstract

Addition of sodium salicylate to human serum at concentrations often obtained during aspirin therapy causes 100-200% increases in free triiodothyronine (T(3)) and free thyroxine (T(4)) as estimated by ultrafiltration. The increase in free T(3) was unexpected since previous data had suggested that salicylate inhibits binding of T(4) only to thyroxine-binding prealbumin (TBPA) and that T(3) is not bound to this protein. Using ultrafiltration techniques, we demonstrated binding of T(3) to TBPA. The affinity constant for T(3)-TBPA binding appears to be slightly greater than that for albumin-T(3) binding. While salicylate inhibits the binding of T(3) (and T(4)) to TBPA, it can be predicted that little change will be observed in the free T(3) (or free T(4)) without inhibition of thyroid hormone binding to thyroxine-binding globulin (TBG). Using a competitive-binding protein displacement technique, it has been shown that sodium salicylate, like diphenylhydantoin (DPH), inhibits the binding of T(3) and T(4) to TBG. The magnitude of the increase in free T(3) and free T(4) induced by salicylates suggests that interference with TBG binding is its major effect. Aspirin was administered orally to two normal subjects in quantities sufficient to obtain serum salicylate levels of 20-25 mg/100 ml. This resulted in a decrease of 20-30% in total serum T(3) and T(4) levels. This decrease in T(4) levels is similar in magnitude to that previously observed in subjects receiving DPH. Unlike what has been observed with DPH treatment, therapeutic salicylate levels are associated with increases of 50-75% in the unbound fraction of both T(3) and T(4) which persist throughout an 8-10 day treatment period.

Open access but full paper is in the form of a PDF scan:

europepmc.org/article/PMC/2...

[helvella Administrator]

This was diogenes' paper (actually just a letter)

Letters to the EditorVolume 321, Issue 8318p245January 29, 1983

THYROID FUNCTION IN LONG TERM ASPIRIN THERAPY

A.F. Giles ∙ T.A. Wilkins ∙ J.E.M. Midgley ∙ A.S. Whitworth

Publication History:

Published January 29, 1983

DOI: 10.1016/S0140-6736(83)92623-5 Also available on ScienceDirect

thelancet.com/journals/lanc...

Unfortunately, despite offering a download, it fails when I try.

[RedApple Administrator in reply to helvella]

'despite offering a download, it fails when I try.'

Me to! 😡

[TSH110 in reply to RedApple]

And me 😖

[Tina_Maria in reply to helvella]

I found the article via researchgate to download (its just a short letter).

researchgate.net/publicatio...

I think if you are on long term therapy, such as aspirin, and your medication is continuous and your blood levels are constant, you can use the value you get with the aspirin therapy as a baseline and look for changes based on that. However for acute use, it is useful to know that FT4 can be depressed, so as you have mentioned perhaps not a good idea to take one before a thyroid function test! 😉

I have noticed that a lot of older papers are now behind a paywall, which is so wrong and why I ask? And very few of the newer papers are offered free, despite the authors having to pay now for publishing in an apparent effort to make them all freely available, so the public has access. Yeah, that one was a dead fish too, as the journals charge the authors AND if you want to access papers. Licence to print money...

[helvella Administrator in reply to Tina_Maria]

I've certainly found a number of papers which used to be open access are now behind paywalls. And when they offer access to what you might know are a sentence or two of actual text (typically a comment letter) and want to charge the same as for a huge great paper...

Officially, papers produced under things like US government grants have to be open access.

I've started making sure I actually download papers while the going is good. It's the only way. But it sure does help when they are already offered as PDFs rather than having to deal with .xml and such like and printing to PDF.

[TSH110]

It was in a reply to a comment I made

I did wonder if it might affect the actual test

it won’t let me post a photo of the comment here - no idea why not

[helvella Administrator in reply to TSH110]

Thanks - I started to wonder if I was imagining it!

[TSH110 in reply to helvella]

I added you in to the bit of the relevant thread fyi. Definitely not imagined!