PSA change from < .04 to < 0.1: Problem or no big deal?

@retireditguy That is the best explanation I have heard explaining the variations in PSA lab results. Thank you.

@ucla2025 -- Your welcome. I just noticed I wrote ",.04" when I meant "< .04". Ugh. I need to get better at proofreading, but clearly you knew what I meant 🙂 Best wishes.

@retireditguy An ultra sensitive PSA test should never be reported as less than .1. Make sure that all tests going forward are done by the same ultra sensitive method.
Results should be reported to the nearest 0.01.

@jeffmarc Good thoughts here Jeff . In this case I was thinking the same thing. Maybe every 3 months is best , as it seems to be bouncing around and is G9 in nature . Could be radiation bounce ...but best he talk to his team to get a full evaluation of what they think and options. I am on every 6 months now (from3 months) . Although I like the PSA anxiety break , I could be sitting on the couch with PSA fluctuations and dont even know it . Im at 0.066 , 5 year post operation , and 2 year post 22 sessions of EBRT radiation. I have been reading up on dormant or normal cells that CAN exist after a Operation , then radiation. The radiation does not tend to kill the healthy cells (normal cells) and goes after the PC cells. More common than I thought . This is what the Dr's say is up with my low level of PSA moving sideways , after operation and radiation. Have you heard of this . Quite common they say . Hope your doing well ... James

How do I find out if my recent PSA reading was based on/ not based on an ultra sensitive test? Contact the Quest lab?

@johnny8924 Sometimes it’s mentioned on the test report.

Also, be sure to ask the right question. There are some ultrasensitive PSA tests that measure down to 0.x, others down to 0.0x, and others down to 0.00x. (The cancer center that I go to measures PSA down to 0.008, but there’s no mention of it being “ultrasensitive.”)

@johnny8924
If the result is reported to two places after the decimal it is from an "ultrasensitive" method. A quick search turned up the following: For Quest the lower limit of accurate quantification is 0.02 ng/mL. Results below this level are reported as < 0.02 ng/mL. Labcorp may report down to 0.014 ng/mL
Labcorp results are said to run about 20% higher than Quest.
Because of differences in calibration and equipment, results from Quest and Labcorp cannot be used interchangeably for serial monitoring. It is recommended to use the same lab consistently to accurately track trends over time.

Here’s what my Quest Lab informed me about the differences in my PSA test results:
“For your test on March 2, 2026, your PSA test was performed using the Beckman Coulter immunoassay method. Result was < .1 .
For your test on November 4, 2025, your PSA result was derived using the Siemens chemiluminescent method. Result was < .04. These results cannot be used interchangeably.

@johnny8924
You still didn’t get the correct answer from them. Was the < .1 Result due to a test that was not ultra sensitive? Knowing what kind of test is done is totally irrelevant Since the Technical information about what kind of test was Dunn doesn’t answer that question.

@jeffmarc Actually, the method information is relevant, but only if you are a clinical lab person. They should have explained that the immunoassay is used for screening or following people who have not undergone therapy for PC. It is not ultrasensitive, as evidenced by the fact that numbers below 0.1 are not reported. This latest result is not informative and the test should be repeated with the order specifying the ultrasensitive (chemiluminescent) method.
Actually, Quest should have done this automatically since a previous result was done by this method.