28 replies to this topic

[Trey]

What does limit quantification of 0.0069% mean?

 

Limit of quantification means the limit of reporting, which for your lab is -4.5 logs.  But most PCR equipment/reagents can detect far below that, probably to -7 logs.  So "limit of quantification" actually means the point at which the results are truncated and no longer reported due to false positives concerns, so it is not a limit of detection.  The limit of quantification is a mixture of how low the PCR can detect tempered by where the reporting should be cut off since false positives rise exponentially below about -4.5 logs. 

 

PCRs were not invented to detect leukemia in people.  They were invented to detect bacteria in foods.  Think of it that way and you will no longer be tempted to expect such surgical precision from these tests.

Edited by Trey, 08 June 2017 - 07:55 PM.

[scuba]

An interesting point of fact on the invention of PCR:

 

http://bitesizebio.c...vention-of-pcr/

 

"Mullis received the Nobel Prize for his ground-breaking invention in 1993. He also received a $10,000 bonus from his employers, Cetus, who later sold the patent rights to Hoffmann La-Roche for a cool $300,000,000. Seems to me there's a lesson in there somewhere..."

[Kali]

Thanks Trey,

That is a very helpful explanation of how to better understand these tests.

It was somewhat confusing. When I would read talk of logs on here, I didn't how to equate that to my PCR test. What you shared helps it make more sense.

[cmljax]

I am still confused.  My last 2 PCR results said the following:

 

Positive. BCR/ABL1 p210 mRNA transcripts were detected at a very low quantitative level (<0.003% of total ABL1 (%BCR/ABL1(p210):ABL1).

 

So given what Trey said, is it possible that my last 2 positive results were actually false positives and could have been negative?  Do some labs report positives below the "limit of quantification" as negatives or do they all report it as positive at a very low quantitative level?

[Trey]

The PCR cut-off is arbitrary, and is different at various labs.  A few still go down to -5 logs, last I knew.  If the positive detection is slightly below the cut-off, then it is probably not a false positive.  But since they do not provide your actual number, only "less than .003%" that is not very useful.  But if a lab has a cut-off, I don't know why they still report the positives unless someone is in a cessation trial, then that might be a reason for clinical trial purposes. 

[hannibellemo]

Just had my annual checkup at Mayo. My onc wasn't even aware that the sensitivity reporting had changed! However, he verified it for me when my PCR results came back that afternoon. Happy to report that I'm still negative even at the new reporting level!

[M.A.]

What great news Pat. So glad to hear you have retained PCRU for 18 months on 50mg. I hope you are enjoying your retirement

[hannibellemo]

Thanks, M.A. I highly recommend retirement, although I could make some suggestions for change. I think we should be happy and carefree when we are young so we have both the time AND energy, and then go to work when we are middle aged and are no longer quite so energetic.  

[kat73]

Great news, Pat - you are my "role model," for 50 mg, no more pleural effusions, and . . . PCRU!

 

I agree, and I wish I could go to college NOW instead of when I was 18.  All that time for reading and 3 square meals a day provided by somebody else.  I would most certainly go to class this time around.