Test results different between labs?

You can't really compare two different tests when the results are close. I don't know if this is also in play, but the two labs may be using two different PSA standards -- Hybritech* and WHO (World Health Organization). By one account this can cause a difference of 23% when testing the same sample. Did you plan on having a re-test at your doc's office in 6 months? If you are going to have a 6 month done at Quest, I would ignore you doc's test. Or a Quest retest comes back <0.02, then take a future Primex PSA result of 0.03 as being the same (unchanged).

If you are concerned, you can have a Quest test done.

Do you know if the Primex equipment is in your docs office or is sent out to them? My doc's practice has Labcorp equipment in office but using a less sensitive (0.05) Labcorp uPSA test. I don't know if in-office equipment is calibrated as often as that in the major labs (I have my blood drawn in his office sent out to a Labcorp facility).

The right-most digit of any test hold uncertainty. When there is only on significant digit in a result -- well, you get the picture. In addition, all test have a margin of error and will not usually give the exact same results when repeated multiple times on the same blood sample.

I wouldn't be too worried.

Djin

Good luck CD, do keep us posted

Hi Cyclone. Regarding <0.1 as undetectable, we should keep in mind that this is based on the standard PSA test for men with prostates after treatment. The metrics and post-treatment dynamics are different for someone whose primary treatment is ADT and/or RT vs a post-RP patient with a pT2 pathology and a very low uPSA. We in the second group would be concerned if our PSA rises from <0.02 to a value of, say, 0.09. especially several years after surgery. Labcorp calls its more sensitive PSA test "ultrasensitive." Quest chose to call its uPSA "post prostatectomy". If you put these adjectives together, you get the intended patients.

For us high-grade, post-RP guys, the decision for very early SRT is made with a rising PSA as well, but one that may be at or below 0.1. It's fine for men with prostates to be followed by the standard PSA test after treatment; however, IMO post-RP it's best suited for G6 men who are pT2 and <0.1.

An overlooked point is that RP men who are given the standard PSA tests for about the first 6 months after surgery will never know their PSA nadir, which has been shown to be a fairly accurate prognosticator of BCR risk. In addition, if faced with a PSA that starts out <0.1 and then rises while followed by this standard test, you have lost data that may point to the start and rate of the rise.

Djin

I went to Quest Diagnostics yesterday and was retested. Will let you guys know the results when I get them.

Quest only goes down to 0.02 ng/ml. So if I was 0.019 ng/ml at Quest it would show up as <0.02 ng/ml (which it always has). If my PSA at Primex Labs was 0.025 ng/ml it would show up as 0.03 ng/ml. So theoretically we could be talking a 0.006 ng/ml difference!

DjinTonic said...
Regarding <0.1 as undetectable, we should keep in mind that this is based on the standard PSA test for men with prostates after treatment... An overlooked point is that RP men who are given the standard PSA tests for about the first 6 months after surgery will never know their PSA nadir, which has been shown to be a fairly accurate prognosticator of BCR risk. In addition, if faced with a PSA that starts out <0.1 and then rises while followed by this standard test, you have lost data that may point to the start and rate of the rise.

The surgeon who did my RP (and I am pleased with his treatment) used the standard PSA post-RP and declared me 'undetectable' based on the <0.1 result, but urged for ART based on adverse pathology. We moved from Ohio to Florida less than two months later and my new Uro started immediately with monthly ultra sensitive PSA's, which came back as <0.02, .02, <.03, .03 etc during my time on Lupron preceding ART. Today, the same Uro tests down to <.008, so I never knew what my "true" PSA was that first month after RP. It has remained at <.008 ever since the first uPSA taken a few months after completing ART.

Getting to the point (finally) I plan to switch to LabCorp starting with my next PSA in January 2021, where my PSA's heretofore have been performed "in house" by the large uro group I've been seeing since moving to Florida four years ago. This is part of my plan to move to another urologist in Tampa next year because of the fallout from my horrible AUS experience and hopefully transition to him to perform the inevitable AUS replacement which is part of the deal with having this type of implant. (Yeah, I know... man plans, God laughs). So I'm prepared for LabCorp's results to possibly differ from what I've been seeing, but as long as it remains flat, I'm good. Fingers crossed.

Best news of the night!

Thankful for this great news, California Dreamer!

Hurray! Hurrah!
CYCLONE - # Iowa State University

Hi TJ123,

Given those ADVIA readings, I'm curious as to which Labcorp test gives you "undetectable" results (i.e., values with a < sign ). AFAIK, there are three different Labcorp tests with a total of 4 different undetectable results: <0.1, <0.05, <0.014, and <0.006.

Djin

TJ123 said...
Djin,

Historically I've had <.006 results from Labcorp (probably 5-6 tests) prior to my last test of <.014. I called Labcorp and asked them why the change to .014. The lab told me the manufacturer changed the lower limit of their test, which is shown on the lab reports to be the Roche ELICIA methodology for both the <.006 and <.014 lower limits. As I mentioned - all my previous tests using the ADVIA Centaur methodology over the last 4.8 years post RALP have shown scant levels of PSA - most recently in the last 3 years at .01.

That's curious about your Labcorp info, because <0.014 was their previous lower limit until about 4 years go. I was under the impression that some folks were still getting a <0.006 results and that it depended on which analyzer you got to run the same Roche assay.

I find it strange that Roche would raise the lower limit of their assay. I have a spec sheet that shows that on the most sensitive analyzers their assay can actually measure down to 0.002 or 0.003. My hunch is that this change has to do with the makers of the different analyzers.

Let's see if anyone does get (or has recently gotten) a <0.006. That will tell us much. (I too got a <0.014 reading for the first time at my last test.) I will check Labcorp results and dates in other signatures, too. Thanks!

Djin

My experience is that the Siemens Advia Centaur is good for doing PSA testing if you have a prostate but does a poor job at ultra sensitive PSA levels if you don’t have a prostate.