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PSA test result 0.1 vs <0.1: doc says it's just noise in the system

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Posted 10/1/2015 4:11 PM (GMT 0)
As I was still wondering what the deal was with the 0.1-vs-<0.1 PSA test result question (some concern being expressed in recent threads about this), I did a little searching and found the write-up linked below, by a doc who seems to know what he's talking about.

Granted the write-up is from eight years ago, but the points it makes may well still apply, since the "less than" question still seems to be around today.

The essence of what he is saying is that the nature of the way these tests work can itself impact the result because of "day to day variations" that occur in the tests themselves.

The write-up (which is really just the doctor's short answer to a patient) gets a little bit technical in describing how these tests work (certainly beyond my understanding), but he does comment that:

"The difference between <0.1 and 0.1 is well within the day-to-day variability of the assay."

and

"Even today it is possible to see some noise in the system that may be 0.05-0.2 ng/ml, depending on the lab and the assay that can introduce day-to-day variation."

Hopefully this sheds a little light on this issue.

www.oncolink.org/experts/article.cfm?id=2464
Posted 10/1/2015 6:43 PM (GMT 0)
Interesting article. We also cannot forget about lab variations and lab mistakes. These mistakes are more common than we think. My husband got a false reading last time he had his blood drawn, confirmed by a re-test. I had a false MRI scan (artifact confirmed by 3 different doctors). PSA marker is indeed an antibody that has been extracted from an animal (usually a goat or a rabbit), then purified, then coupled with an enzyme - the sponge method described in the article may be a different one, but the one I am familiar with, is a reagent solution. It is very much a biological behaving complex, and prone to variation.
Posted 10/1/2015 7:12 PM (GMT 0)
bear in mind that article is from 2007. After my doctor, the uro that diagnosed my Pca, did my first 6mo. post surgery follow up psa and gave me the <0.1 result and told me the "noise" theory I left him and I have for the last 4 years used my GP for follow-up psa. My GP sends it out to a lab that gives the result in 2 decimal places ie, X.XX. While I entirely agree with my old uro that X.X is appropriate for diagnosing Pca, I am not comfortable with that for my follow up. In light of the recent Johns Hopkins article posted by Tall Allen about 0.03 becoming a reliable predictor for recurrence I am even more sure I don't want any thing less that two decimal places. I think the "noise" theory is something that might have been relevant 10-15 years ago but not how.

Post Edited (knotreel) : 10/1/2015 1:17:16 PM (GMT-6)

Posted 10/1/2015 8:11 PM (GMT 0)
I agree with knotreel completely. Technology has changed since 2007. Yes, there can be day to day variances or"noise" but accurate testing at 2 or even 3 places to the right of the decimal point are readily available if you choose to avail yourself to them. That is between you and your doctors. The less than sign (<)simply means what is represent- less than whatever number.
Posted 10/1/2015 10:09 PM (GMT 0)
The referenced article relates to patients after HT or RT, not RP guys like me. HT and RT guys still have their prostate glands, so it seems probable there will be fluctuations at the lowest levels, and there should be no reason for concern. I don't think HT or RT guys would get any value from a uPsa test. However, for RP guys, without their prostate glands, there is a much greater level of concern. We're not supposed to have any prostate cells. It could be "noise" but it could indicate that some of the cancer cells have survived, usually in the prostate bed. They may do nothing, hopefully just die, or they may multiply and eventually spread. If a uPsa of .03 indicates an a strong likelihood of eventual BCR, (for RP), then it seems the uPsa is a good tool to help decide whether to hit it early with SRT. With so many variables, it's just a crap shoot.
Posted 10/1/2015 10:12 PM (GMT 0)
actually, 'noise' issues will get worse the lower the detection limits go. As the level of 'significant error' goes down, the likelyhood of introducing that error goes up. There was a comment a week or so in here about some researcher has claimed he can measure PSA to 0.000035 ng/ml. Which is, literally, a claim that they can detect a single molecule of the PSA protein in 1 ml of blood. To get that, the laboratory conditions have to be nearly perfect.
Posted 10/1/2015 11:12 PM (GMT 0)
I get a lot of issues with noise, but I find if I just turn my hearing-aid off, it doesn't bother me anymore.

Andrew
Posted 10/1/2015 11:19 PM (GMT 0)
Halbert, the scientist, hit the nail on the head with surgical precision. There is a lot of misunderstanding about PSA test results that results in anxiety about insignificant differences in PSA results between tests at one lab and between labs.

If you are confused, please read this excellent article on precision, accuracy and reproducibility. It can allay a lot a fears and counter many misunderstandings about PSA testing.

/labtestsonline.org/understanding/features/reliability/start/1/
Posted 10/2/2015 12:43 AM (GMT 0)
Tim, that is an excellent article, and it's not written in "tech speak".
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