How accurate are the PSA Tests?

Recently I read that the lab you select to do your PSA test should be the one to stick with forever. The reason as I recall is that each lab performs the test differently. So LabCorp results may differ from Quest Diagnostics and others. The Prostate Cancer Foundation says "Should I use the same lab for all my PSA tests?
It’s important to try to always use the same lab for all of your PSA tests because PSA values can fluctuate somewhat from lab to lab. After radiation therapy, doctors need to look for confirmation from multiple tests because PSA can “bounce” or jump up for a short period, and will later return to its low level." This low level in medical terms is referred to as the Nadir or the lowest point. Yes, pause the bike riding and throw away all of your Playboy mags. Be sure to do what Luke was told in Cool Hand Luke "Boy, get your mind right".

Can you clarify? What do you mean by less than 0.03 being the lowest they go. Surely your previous reading at less than .006 after surgery was lower or did you mean 0.003?

The importance of at least considering a retest is crucial here. Like your old woodworking class mantra; "measure twice, cut once".

PSA 7.8 then on Xtandi 1.7 then 2.3 then 3.0 do I worry

@ozelli. The tests were from different labs and evidently each lab has different lower limits. I assume Labcorp lowest limit is the < .006 score, (where I had my .006 and .117 scores) . Johns Hopkins, where I took the retest has a lowest limit of .03. They state this in their description:
"Limit of detection of 0.03 ng/mL" , which is what Dr. Walsh also mentioned. Before I started the ultrasensitive tests, when I was going through my primary doctor, his lab's lowest limit was < .1, which were my earliest scores post surgery.

The proper use of PSA is for "tracking" or monitoring levels over time. Sometimes, the specific method used is appended to the test.

When detecting PSA is used to evaluate radical prostatectomy , where one is hoping to find no PSA, or post-radiation, where one hopes for very low levels, then knowing something about the assay itself becomes far more important. Both the detection limit should definitely be specified with the result, also the manufacturer of the test. Example on my PSA lab result:

Method: Roche-Electrochemiluminescence
WARNING: The concentration of PSA in a given specimen
determined with assays from different manufacturers can
vary due to differences in assay methods and reagent
specificity. Values obtained with different assay methods
cannot be used interchangeably

I would say wait until your PSA number settles down to its lowest level (the Nadir). Here are some very good articles regarding prostate cancer recurrence after surgery/radiation.
https://www.hopkinsmedicine.org/health/conditions-and-diseases/prostate-cancer/prostate-cancer-prognosis
https://health.usnews.com/health-care/for-better/articles/2018-04-20/the-realities-of-prostate-cancer-recurrence
https://sperlingprostatecenter.com/what-to-do-if-prostate-cancer-comes-back-after-radiation/
https://www.webmd.com/prostate-cancer/guide/prostate-cancer-recurrence

Thank you for your detailed post. I, too, am post-surgery (15 months), and on a regimen of PSA testing every 90 days. Thankfully, thus far, it's been undetectable. Your post reminds me/us to stay vigilant, and to be ready to react to "what if" situations that may arise.

Hi, if your Psa goes above 0.03. I will inform your neurologist, and let them take action. Hope this advice is helpful..

I have not had my first PSA test after radiation (Proton) treatments. It was 3.75 prior to treatments. I am on of those individuals showing you can have prostrate cancer and still have a normal level PSA.

My Oncologist/Radiologist at UFPTI in my post treatment information stated the same thing about testing. That it should be at the same lab each time due to difference in labs which will affect the numbers. I am having my PSA test done at Mayo and my primary care doctor stated the same, to make sure I did each at same lab.

I am a little confused with some postings. What is considered a good PSA number after treatments. Is the first PSA after treatment not a good predictor of success or failure? Is the norm that your prostrate is still inflamed and irritated for the first PSA test which I assume is 3 months at most providers like mine is scheduled for.

I did read about biking. My primary care doctor and I were well informed about this as we thought my rise in PSA numbers was caused by bike riding as I was riding 25 miles couple of times a week. Then we did a plan not to ride 48 hours prior and then 72 hours. It went down a little first time but then rose again second time. It is then my primary care doctor referred me to Urologist.

Here is what I've found for you about PSA readings. The Hopkins site says "After treatment with radiation, PSA levels rarely drops completely to zero. However, the PSA should level out at a low number, which is called the nadir. When PSA rises 2 points from its lowest value, the cancer is considered recurrent." If one has had surgery it says "After surgery, PSA levels should drop to zero. When PSA levels rise above 0.2 ng/mL, the cancer is considered recurrent." Scroll down the page to the section labeled Long-Term Prognosis and read from there on down. (The source for above info is https://www.hopkinsmedicine.org/health/conditions-and-diseases/prostate-cancer/prostate-cancer-prognosis)
The next site says "The pattern of the drop in PSA after radiation therapy is also different from after surgery. PSA levels after radiation tend to drop slowly, and might not reach their lowest level until 2 years or more after treatment." Next, read the section labeled After Radiation Therapy (source is https://www.cancer.org/cancer/types/prostate-cancer/treating/psa-levels-after-treatment.html)