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Posted 3/23/2010 8:33 PM (GMT 0)
We are told that one should have psa tests at the same lab and using the same assay (and, I have seen Dr. Strum recommend, at the same time of the day).  I will share a lesson I learned about "same doc and same lab does not mean same assay."  My primary care doc uses Quest Diagnostics.  When one orders a total psa test from Quest, they use the Seimens (Bayer) chemiluminescent method.   But when one orders a total psa and free psa, Quest uses Beckman-Coulter.   So, same doc and same lab, but not same assay.  

I asked Quest why this is and they responded.  The reasons are historical and I won't waste your time with them unless someone is interested.  Doesn't really matter.  The point is "same doc and same lab doesn't necessarily mean same assay."

And the assays are not comparable.   So if you are one who believes in the importance of psa velocity/trend/kinetics, you want to be using the same assay every time.

And I don't think most primary care docs will be helpful here.  Mine is really good, but I am almost certain he does not know about the importance of using the same assay for every psa test.  And I am absolutely certain he does not know the difference between the Siemens (Bayer) method and the Beckman-Coulter method.  And I am even more absolutely certain that he does not know that if he orders total psa, he gets results using one assay, while if he orders total and free psa, he gets results using a different assay.  (I will tell him this when I see him in a few days -- then he will know).

I hope maybe this is helpful to someone.

Medved

 

Posted 3/23/2010 8:38 PM (GMT 0)
Med,

I fully agree with what you are saying, and my own uro/surgeon is real strict about that when ordering tests, we discussed this very subject recently. Good tip
Posted 3/23/2010 8:38 PM (GMT 0)

That's some serious "in-the-weeds" info, Medved..thanks for sharing it. The more we know, the more we learn we don't know :-)

Arnie in DE

Posted 3/23/2010 8:53 PM (GMT 0)
How does a person know that a lab is goodconfused

Doesn't going to a second lab help?

If one lab says your psa is 2 and another lab says its 200 - then you have a red flag situation and go to a third lab.

Posted 3/23/2010 9:02 PM (GMT 0)

medved said...
When one orders a total psa test from Quest, they use the Seimens (Bayer) chemiluminescent method.   But when one orders a total psa and free psa, Quest uses Beckman-Coulter...

   

I asked Quest why this is and they responded.  The reasons are historical and I won't waste your time with them unless someone is interested. 

I'm interested...

(Whether they told you this or not, I'm going to guess that when one gets to the bottom of why, it will be cost related.  They are, after all, a business.)

 

Posted 3/23/2010 9:47 PM (GMT 0)
The reason they gave me is at the time they began doing free psa testing, Siemens did not do free psa, so Beckman Coulter was their only option.  (And when you do free and total, you need to do it on the same instrument).  However, Beckman Coulter could not handle the volume of total psa tests the lab generated (it is among the largest labs).  So they were compelled to do total psa tests using one assay and total/free (of which there are far fewer) using a different assay.

As an aside, there seems to be some unresolved issue about the lower level of total psa at which free psa is potentially relevant.  Dr. Strum suggests that level is probably 2.0 or 2.5.

 

Posted 9/8/2012 10:45 PM (GMT 0)
medved,

Did anyone ever tell you what <.1 Beckman Coulter means as compared to <.03 Siemens Bayer?

Posted 9/8/2012 11:29 PM (GMT 0)
Beckman Coulter assay machines are calibrated using the Hybritech standardized material. If a different assay machine manufacturer uses the W.H.O. standardized material to calibrate, the results will differ from Beckman Coulter by 20% e.g. a 4.0 PSA from a Beckman Coulter machine will be 3.2 on a W.H.O. calibrated machine. I discovered this during my own PSA tests and subsequent investigation of results from different labs. I now always specify that my blood sample is to be sent to Quest and both total and free PSA will be reported. So far all total and free tests have been done on Beckman Coulter. I may need to specify Beckman Coulter also. By the way the 20% mentioned above was found in an article on the American Association for Clinical Chemistry website.

Robert
Posted 9/9/2012 11:34 AM (GMT 0)
Curm,

Thank you for the information.  It certainly is disconcerting when one receives test results that vary by as much as 20%.

Mr Bill

Posted 9/9/2012 7:59 PM (GMT 0)
We have discovered the same thing. John has his PSA done at the hospital and also at an outside lab. The outside lab is way higher consistently. so, we compare apples to apples!

Last week we were telling this to our family doc. He replied that his wife had her cholesterol checked at the same outside lab and then at the hospital and that it was high in one place and low in the other. He is puzzled.

I guess the lesson is to not put too much stock in any one test. Look at the trend instead.

Oci
Posted 9/9/2012 9:47 PM (GMT 0)
I had the exact same experience as Medved at Quest. It is quite a surprise that the Uros i saw were not as concerned even when I brought it up. Very strange since the trend of my PSA scores was used as a reason for Bx, yet differences in the assays used were ignored. I wonder if they will feel the same if it happens to them.
Posted 9/10/2012 12:25 AM (GMT 0)
Primary care docs and even some urologists seem not to focus on this important issue. And it is beyond what can reasonably be expected of an average patient. Curm's explanation is a good one, though to make the matter more complicated, there is some variance even among the WHO calibrated assays. I think best a patient can do is get each PSA test at approximately the same time of day, using the same lab AND the same assay.
Posted 12/12/2012 12:32 PM (GMT 0)
It seems now even the ambient temperature may affect the PSA test.  At least that is what I get from reading the below information.  I may be wrong (not the sharpest knife in the drawer), so please correct me if you read something different.

http://www.biofind.com/rumor-mill/siemens-fda-warning-letter-june-2012

Posted 12/15/2012 3:14 AM (GMT 0)
I am glad I read this post because this issue just came up with my readings.

My PSA has been slowly rising and we have been watching it. Last December it was 4.24 from a lab that used COBAS E. The doc ordered a free PSA test 2 weeks later it was 5.4 from another lab that used the Beckman Coulter. Unfortunately he only told me about the Free PSA % and I didn't know about the 5.4 Total PSA reading because I didn't get a copy of the lab.

In April we checked it again and it was 4.31 from the same lab using COBAS E and now in November it is 5.49 from the same lab.

When I saw the Uro a few weeks ago he thought everything was Ok since the numbers hadn't changed much since last December at 5.4 and now 5.49. But it is comparing apples and oranges seems to me. The PSA using the same analysis has gone up from 4.3 in April to 5.49 in November. Unfortunately I didn't have all the lab work paperwork to make my point but I did it get it today and will be going back to see him so we can get this straightened out. I think it is time to do a biposy:(

Steve
Posted 12/15/2012 10:52 AM (GMT 0)
My post dated 12/12/2012, regarding ambient temperature and test results, should be disregarded. I misinterpreted the information provided in that link.

Sorry,
Mr. Bill
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