I see that a PSA number is represented in two different measures. Sometimes I see just a 1 to 3 digit number (ex. 15) while other times it's represented as a decimal number followed by ng/ml (ex. 0.0025 ng/mL). Is there a conversion involved?
Thank you for any information you can su[[ly.
I believe that both numbers are ng/ml (or ng/mL), but quite often that is just assumed rather than stated. A PSA of 15 is higher than normal and probably indicates either cancer or prostatitis. A PSA of 0.0025 is extremely low and almost certainly indicates that a person had his prostate removed and has no current sign of cancer. Only the "ultra-sensitive" tests can detect a value that low. It would be reported as "undetectable" by other testing methods.
Alan
Perhaps the number only, e.g. 15 is over ONE. Really, if this is the case, it should be written as 15.0 Otherwise 15 on its own is meaningless, is it 15.0 or is it 0.15 or even 0.015, 0.0015 etc?
I once worked with a doctor who was in the habit of ignoring the decimal point zero of a drug dose if it was over 1. We had a patient transferred to us from somewhere, his notes said he was prescribed 1.0 mg diazepam.
He prescribed 10mg
It was only when the patients' relatives asked if we were sedating him that I picked this up.
So it's IMPORTANT to get it right.
On the other hand, since I believe, officially, it isn't counted as biochemical recurrence until PSA reaches 0.2 ng/mL does the test really need to be more sensitive than 0.01.
It's scary enough enough having a test every six months and worrying that your PSA has gone up. As long as it stays below 0.01, what's to worry about. Knowing it's gone up from 0.0015 to 0.0016 for example would just make it more scary for me.
I've always been a person who copes with problems by finding out as much as I can about it, then taking action. Since being diagnosed with prostate cancer, I find that sometimes, there''s things that really it does you no good to know, and you don;t really need to know.
I once read recently that there's a special kind of MRI that can pick up metastatic tumours of an incredibly small size. My thought is, if it's so small it isn't YET causing any harm. AND since it's so small how could you realistically treat it with radiation and its collateral damage , is it worth having chemo or hormone therapy with its side effects when it's not YET doing any harm. Not perhaps so much in the UK, but I'd ask, how much do medical practitioners try to sell you treatment that isn't really necessary.
Eventually, imagine, they'll invent a detector that can detect a single prostate cancer cell as it travels around in your blood or lymphatic fluid. They'll have to invent a miniaturising ray, like in the movie, "Fantastic voyage". They can send a microscopic submarine into you, chase down the metastatic cell and zap it with a laser.
youtube.com/watch?v=-hjiVVi...
Tim,
Forgive me for picking a nit or two on numbering.
15 and 15.0 are different in that one is two significant digits and the other is three. Because PSA is a measurement, not an exact number, a scientist would use the number of significant digits to determine the precision of the measurement. "15" would mean a number between 14.5 and 15.49 and "15.0" as a number between 14.95 and 15.049.
I like the convention 0.01 when it's desirable to emphasize the decimal point. Unlike trailing zeros, leading zeros don't count as significant digits. 0.0000006 has one significant digit. 0.00000060 has two.
I think your points about not needing measurements below 0.01 is well taken. There is a tiny amount of PSA produced by the adrenal gland. It has nothing to do with cancer but it will show up in ultrasensitive tests. I seem to remember reading that it can be as much as 0.03, but I haven't tried hard to verify that.
One thing that we should realize is that PSA measurements can vary for reasons other than cancer growth. The adrenal gland might produce a tiny bit more one day than another. There may be tiny bits of non-cancerous prostate tissue that are still alive in the body and still producing tiny amounts of PSA. The concentration of molecules of PSA might happen to be slightly greater in one blood draw than in another even if the total PSA in the body hasn't changed. In line with our understanding of significant digits we should recognize that 0.0015 in one measurement might actually be 0.00154 and 0.0016 might actually be 0.00155 - a trivial difference indeed. And finally, of course, the technology used in measuring isn't perfect and neither are the technicians who employ it. Tiny changes in test conditions and calibration can occur and tiny traces of contaminants can appear in the blood draw, the container the blood is kept in, or the instruments that the blood passes through.
So, yes, I agree. Don't treat very small changes in PSA reports as meaning anything at all about cancer.
Alan
Thanks Alan, a lot of sense in what you say. I even hear that test results differ between one laboratory and another.
Thanks also for your theory about what "15" means in comparison to "15.0". You may be right, luckily, the highest my PSA ever got was 6.4.
I did come across a guy on this site though who said his PSA was 27.8. Which leads me to ask why isn't a measurement an "exact" number. Surely if a test is capable of detecting an amount as small as 0.01 ng/mL then it is capable of measuring differences as small as that. A difference of one hundredth of a billionth of a gram is pretty exact.
Mind you, wouldn't want to take that too far. If measured in kilometers the British coastline is 12,429 km. If measured in meters, it would come out longer than that, because some features of the coast are less than 1 km in length. If measured in centimeters it would come out even longer because some features are less than a meter long, in millimeters longer etc. The length of the British coastline is potentially infinite. I wouldn't want my PSA to be infinite!
Compromise is a good thing.
fractalfoundation.org/resou...
It turns out that there is more than one technology for testing PSA. They have different sensitivities. The one that does "ultrasensitive" testing is not used (and presumably not useful) for PSA values above for anything but very low values and vice versa for the testing methods that are used for higher values.
In any case, learning that your PSA is 27.8015 is probably not more useful than learning that it's 28. Not only would you never make any decision based on whether it was 28 vs 27.8015 but, because PSA varies a bit from day to day for unknown reasons, you'd be getting different results every day, and probably every hour, from the ultrasensitive test. Three significant digits are probably not clinically significant.
Incidentally, there are men in this group, still alive and kicking, who had PSA values in the hundreds and even the thousands before treatment.
Alan
Thanks, I'm with you on that. Lets agree that PSA as a diagnostic test is pretty awful .
Yes, PSA testing has significant limitations. It was a revolution when it was introduced and it probably saved thousands of lives, but the science keeps advancing and I think better procedures are already in the pipeline.
Alan
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