Monday, 5 September 2011

Just had a lovely e mail from one of the Urology Nurses at Addenbrookes with a very detailed explanation that is worth sharing on the Blog for those interested in the testing process...

Hi Dan

Sorry you’ve had no luck with your result, and I have to say that I’ve just looked it up to find that the final result is still pending ….. but I am very confident that this will come back at <0.02 as usual.

What happens with the samples is that they go to the lab where they are centrifuged to separate the blood cells from the serum – the serum is the useful bit, so this is then tipped into another tube and the PSA reagent added, then a spectrometry machine will read the sample to get a figure.  For your normal, run-of-the-mill PSA level (i.e. the man on the street without having had surgery) this result is very quick to get, perhaps a day or two.  However, when the PSA is so low, (as yours is, reading at less than 0.1), the spectrometer isn’t always accurate enough, so the sample has to be further diluted and more reagent added, then re-read with another much more sensitive machine (expensive & time-consuming, so not done as a matter of course).  It is this second process which leaves us dangling without the final result, which is so frustrating.  It is only when they can fill the second centrifuge with approx 100 samples needing the really sensitive reading that they will turn the machine on, so if we’re lucky this can be the next day, or if not, we might have to wait 4-5 days before the final result gets entered onto the computer system…… and that’s where we are now.  However, because we like to work with a sensitivity of two decimal points, we always do this “super-sensitive” assay – some hospitals don’t bother, but we feel that a man with a PSA of <0.02 is absolutely fine, whereas if this figure starts to climb to 0.03, 0.04, 0.06 etc, we can detect miniscule recurrence at a very early date.  If we were to work with only one decimal point, we would lose that time benefit whilst your reading stayed at 0.1 (for instance) for ages, whereas in fact your PSA was slowly rising behind the scenes!

I hope this long-winded waffle helps you understand why the result is not on the computer system as quickly as we would like, but rest assured,  I will look out for it every few hours and email it to you (or text it to you) just as soon as I have it.


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  3. John Sargent23 September, 2011

    A hugely useful posting, Daniel, and a thought-provoking one, too. Amazing to relate, but the lab that does my PSA tests (here in Trieste, Italy) works to three decimal points,and the results are available in the afternoon of the day following the taking of the blood sample.

    I daren't ask my local lab for fear of giving offence, but I'm beginning to wonder what's going on, and why they are so quick in coming up with the results!

    Lab assays are a topic that is rarely discussed in prostate cancer forums, yet they provide us with the indicator - PSA - that is of central concern to us and our families. So it was most useul to have the detailed description of the methodology.

    Many thanks!



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