6 replies to this topic

[BPilgrim]

Hi all.  Question for anybody with knowledge about this...

The lab that currently does my PCR testing has a quant limit of .0069 on the IS.

There is another lab I've leanred of with a more sensitive limit of .0032 on the IS.

Is the .0037 difference between their quant limits significant enough that I should consider the .0032 lab?  Or is the difference negligible at those lower ends of the scale?

Thanks.

[PhilB]

One goes down to a 4.2 log reduction, the other to a 4.5 log.  There's then the question of do each have a level of detectable, but not quantifiable before they declare PCRU so you can't necessarily say which would make you PCRU first.

At those levels you are doing so well that it really isn't worth worrying about.  The only question therefore is how much would you worry about it anyway.

Phil

[BPilgrim]

I am in that situation of getting a "weak positive" result that detected bcr/abl but cannot quantify it.  I asked the lab how they considered me to have lost my PCRU of 8 years for the "weak positive", yet cannot give me an amount of bcr/abl cells they detected.  They simply said they 'detected something, but not enough to quantify it.'  I'd like to know if it was .00001% or .0068%, but I guess I'll never know. I thought maybe the other lab's more sensitive test would give me a better chance of tracking the CML, but maybe not since the log reduction sensitivity is minimal and gets hazy at those low levels.

Anyway, I try not to worry.  I'm not always successful.

[Trey]

The labs chose a point in the PCR at which they say "enough already -- past this point the data is garbage".   Some labs accept more garbage than others.  Accepting more garbage does not tell you that there is an actual problem.  Your current lab is likely good enough, since -4.5 log is a generally accepted cut-off for PCRs.  Wait for another PCR to see if there is an issue.

As a factoid of little value, many PCR labs have fine print that says their PCRs are for research use only, and not for use in patient diagnostics.  That should tell you something.

[BPilgrim]

Thanks, Trey.  I'll post when I get my next PCR results.

[BPilgrim]

I said I would post my October PCR result following my curious "weak positive" result in September...

I am back to 'undetectable', which is a relief.  This is now the second time I have returned to 'undetectable' following a "weak positive" result one month prior.

I still wish I knew for sure what causes this 'jumping around' in results.

Be well, everyone.

[CallMeLucky]

"I still wish I knew for sure what causes this 'jumping around' in results."

The tests are just not that good.  Aside from the variation in the machinery itself, there is a human element to it.  Its nerve racking because we hang it on so much, but the reality is that the tests are approximations.  Very sensitive approximations, but still approximations.