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Anyone “below detection" with an ultra sensitive PSA test?
Following radiation therapy for a local recurrence, I am now doing quarterly ultra sensitive PSA tests through Labcorp. My understanding is that the lower limit of detection for these ultra sensitive tests is around 0.01 (can be higher or lower depending on the assay method)
But for anyone doing ultra sensitive PSA tests, have you got a result that was below detection, whatever that exact lower limit is?
I had a RARP in 2025, and for the ten years before my recurrence, I only did regular PSA tests with the lower limit of detection of 0.1. I was always below detection until June 2025 when I tested at 0.11.
Anyway, I’m just wondering how low PSA can go, especially in guys who have had a prostatectomy. Theoretically, without a prostate and no residual cancer, PSA should be zilch/nada/zero. But I don’t have a recollection of anyone reporting PSA as undetectable on an ultra sensitive test. Can anyone say otherwise?
As a secondary question, if PSA never reaches “absolute zero” following a prostatectomy, does that imply that there are some cancer cells lingering? What is producing PSA, even at levels of say, 0.001-0.008, in a guy without a prostate?
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@melvinw Ultrasensitive PSA is medically meaningful in my specific situation (stage 4b, currently fully suppressed with ADT+Erleada):
< 0.01 (not detectable) means anything borderline that shows up in scans doesn't require too much additional investigation, beyond some follow-up scans to ensure it's not changing
>0.01 (detectable) could trigger biopsies or other more invasive tests for a borderline imaging result (or in the case of my thoracic spine, precautionary radiation, since the spinal fusion means it can't be biopsied).
My original cancer was very aggressive — I went from a twinge in my back to paraplegic in about 5 weeks — so I don't necessarily have the luxury to wait and see if something starts growing again.
I also recognise that my case is atypical (my original oncologist told me only about 5% of prostate cancer behaves like mine did).
Agreed that once it's detectable, it doesn't matter much whether it's 0.02 or 0.05.
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1 Reactionafter i started ADT in July'25 and radiation in early Oct'25, my PSA went from 71 to < .02 ( Oct 26th) and after Dec it has been < .01 ( last draw March 26 )
. hope it stays down..it is nerve wracking each 3 month draw..
This article discusses implications of uPSA value of 0.03 after RP - according to this research this specific value predicts BCR in making. I am posting this just to say that uPSA has its value and predictive potential in some circumstances.
https://pmc.ncbi.nlm.nih.gov/articles/PMC4527538/
@melvinw LabCorp charges 5x as much for uPSA that goes to .002 vs. their standard that goes to .1; so now more of a commercial / marketing reason (LabCorp is the only one to go to 3 decimals) vs. medical. The standard Quest PSA goes to .02 and is priced competitively with LabCorp's standard PSA. Most labs report to 2 decimal places on standard PSA tests now. There are over 5 different methods of PSA lab analysis. Quest, LabCorp std., and LabCorp uPSA use 3 slightly different methods. That is why it is recommended to get the PSA with the same lab. LabCorp may report standard PSA to 1 decimal to market their uPSA test. Other labs us the same PSA analysis and report std. PSA to .02.