Please Welcome New Member rtom

In another thread new member rtom said.....

"Had my RP June 2020 and was fortunate to get down-staged when they looked at the resected prostate. No cancer in nodes or seminal vesicles, no positive margins, 3+4, maybe 30% 4, tumor maybe 5% of the prostate but was present on both sides.

PSA was undetectable until Sept 2022, when the Beckman DXI machine my doc uses came back with a barely detectable value of 0.01 (which is their lower limit of detection).

Once my doc starting testing me only every 6 months, I have been going to Labcorp every 3 months, with an undetectable uPSA of <0.006 each time -- including a test in October 2022 (a month after the DXI value of 0.01).

I know you can't compare numbers between the different assays, at least in a quantitative way. Just wanted a second independent reading.

But just today I got a value of 0.03 from the Beckman DXI machine, just 3 months after the 0.01 number from the same machine. Not reasssuring, and a bit surprising since I went over two years undetectable by both assays.

I'm assuming there is some error in both assays and it does seem likely that I don't actually have a PSADT of less than three months. But I am going to go back to Labcorp to get another reading from their Roche machine. And my doc will re-measure in 6 weeks on the Beckman DXI machine. Will try to be patient!

I am however wondering what people's thoughts are on differences between assays when the numbers are low (0.01 to 0.1).

Thanks for any thoughts."

rtom - Like Pratoman indicated, doubling time calculations with really small numbers that may be +/- 0.01 and from different labs is a wasted exercise. I might suggest staying with one lab and get your tests on a regular interval, makes the math easier and one less variable. You can pick the lab with the better numbers if you wish but a real problem will become apparent soon enough if there is one. Your next step will be decisions at a much higher PSA level where something will show up on the PSMA scans. I have stayed with <0.10 testing since I will not do anything until I get past that number so why worry. My urologist said I could go on annual testing if I wanted which surprised me but it made me think about it. There is a balance between getting the info you need and the anxiety of getting info that is not particularly helpful.

Thanks all for the welcome and advice!

I guess I know that PATIENCE is the best thing I need to practice right now.

In February I will re-test with my doc's DXI assay, and I do think I will also get the Labcorp Roche assay taken the same day. I know enough not to lose any sleep over this: I am a PhD biochemist and I run assays myself at work, so I am familiar with the kinds of systematic and non-systematic errors one gets. But also really good to talk to people who have already trod this path!

rtom said...
I am however wondering what people's thoughts are on differences between assays when the numbers are low (0.01 to 0.1).

Thanks for any thoughts."

Hi, rtom, welcome aboard. I am the fellow whose old post you originally appended to. Better to have your own thread. I am a bit above the "low" range you inquired about, but, oh, well..

Some pointers/suggestions:

(1) yes, the numbers between assays will vary;

(2) yes, the numbers within assays will vary, even over relatively short time intervals;

(3) really hope you are truly undetectable and stay so, but if not: try not to stress too much on all this, be patient, stick to some reasonable testing interval, keep consistent blood draw conditions (time of day, body hydration, similar meds, avoiding biotin, etc.).

(4) try to stick with one assay, but, as you have done, switch to another assay if needed to "sort things out".


I almost always use LabCorp, But here's an example from my data showing my disbelief in a LabCorp Roche number and switching to Quest Beckman Coulter DxI to recheck:

2020/09/28: uPSA = .055 td = 1006

2020/10/26: uPSA = .306 td = 1121

2020/11/02: uPSA = .05 td = 1016 (Quest)

2020/12/28: uPSA = .058 td = 1003



Here are some of my data from this year that show how results may jump around, even with the same assay and trying to control blood draw conditions:


2022/02/25 uPSA = .106 td = 0936

2022/04/15 uPSA = .122 td = 0944

2022/06/29 uPSA = .106 td = 1004

2022/09/09 uPSA = .141 td = 0958

2022/09/30 uPSA = .106 td = 1043 (recheck)

Hard to believe, but those are the numbers on my lab printouts.

Seems to me there is something going on here besides true blood uPSA values, but darned if I can figure it out, and nobody else can tell me, either--and, yes, I just went back through all my printouts to make sure those were the reported numbers:


Finally, I would like to give you the notes printed on my Beckman test and Roche tests, in which they explain about their assays. But with your expertise, you probably know these things already.

Welcome aboard, and let us know how we can help.

Robert

ps: just noticed I last updated my profile "last PSA" in 09/2021, at .108. Now, a year later, it is .106. Is that a negative doubling time (ha).



====================================

REFERENCE RANGES for PSA:
LESS THAN 0.10 ng/mL AFTER RADICAL PROSTATECTOMY.
4.0 ng/mL OR LESS IN HEALTHY MALES WITHOUT PROSTATECTOMY.
PSA values obtained with different assay methods or kits
cannot be used interchangeably.
This test was performed using the Beckman Coulter DxI
method. PSA, ICMA is not to be used as a diagnostic
procedure without confirmation of the diagnosis by another
established product or procedure.
The lower limit of accurate quantification for this assay is
0.02 ng/mL. PSA values less than 0.02 ng/mL cannot be
accurately measured and will be reported as less than 0.02
ng/mL. Specimens with PSA levels below the lower limit of
accurate quantification should be considered as negative. In
patients with a negative result for post prostatectomy PSA,
serial monitoring of PSA levels at regular intervals, along
with physical examinations and other tests, may help to
detect recurrent prostate cancer.

====================================

Roche ECLIA methodology.
According to the American Urological Association, Serum PSA should
decrease and remain at undetectable levels after radical
prostatectomy. The AUA defines biochemical recurrence as an initial
PSA value 0.200 ng/mL or greater followed by a subsequent
confirmatory PSA value 0.200 ng/mL or greater.
Values obtained with different assay methods or kits cannot be used
interchangeably. Results cannot be interpreted as absolute evidence
of the presence or absence of malignant disease.