Monitor my Health private thyroid testing have replied to my query regarding a FT4 result from their lab differering from the FT4 result from GP when blood from the same draw was used for both tests. The last sentence is most interesting to me, that blood drawn from the arm is the same as a finger prick test.
“Without knowing the analytical platform used by the laboratory which your GP uses, it is very difficult for us to comment on the very slight differences in the FT4 concentrations reported.
Just because the same reference range is quoted, one cannot assume it is the same platform or assay used. Slight variations in results are often seen due to the biological and analytical variations, and potential differences in pre-analytical handling (post vs same day delivery and analysis to a laboratory), which must be factored into any laboratory results when reported. That said, clinically and biologically, there is absolutely no difference in reality between a FT4 result of 18 vs 15.9 pmol/L.
What I can say is that in 99% of cases, thyroid stimulating hormone (TSH) is the most sensitive and accurate marker of thyroid function. Many laboratories used a tiered structure for testing thyroid function, and test TSH first. If the TSH is normal, i.e. within the quoted reference range, then most laboratories do not add on a FT4.
In essence it would not produce a different result from venous or capillary.
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Bearo
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Good to know that there is no difference between venous and fingerprick, very reassuring.
However,
That said, clinically and biologically, there is absolutely no difference in reality between a FT4 result of 18 vs 15.9 pmol/L.
So with their ranges that 60% through range vs 39% through range and they say there's no difference. Makes you wonder why there is an FT4 test then.
I wonder why I feel so very different when my results are 81% through range vs 60% through range.
Maybe the medical profession should just go back to taking patients' symptoms into account like they did years ago and forget blood tests altogether (I'm in a grumpy mood this morning!).
"That said, clinically and biologically, there is absolutely no difference in reality between a FT4 result of 18 vs 15.9 pmol/L."I wonder if they are so cavalier about TSH differences ?
If so , can we all start telling the GP's to 'shove it where the sun doesn't shine' because 0.05 is near as damnit the same as 0.5 ?
I've been told point blank by a G.P. that results obtained from a finger prick draw aren't as reliable as a venous blood draw. My sister is a nurse and said similar after I asked why I'd had to provide so much blood (I had four vials taken for several tests) Is it just with regards to thyroid testing specifically?
That's why I prefer to get a blood draw over a finger prick result if I can. Interesting though.
I agree it’s defensive. This is actually their second reply as the first was more defensive and also more vague. I used venous blood for both tests and I wanted confirmation that their test could cope equally with venous or capillary blood, as I might use the surgery for the blood draw next time.
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