You are here

The meaning of an undetectable PCR

Categories:

All,

I am keen to find out   if anyone has explored the meaning of a PCR of  undetectable .

August 2016 my PCR was 0.266 and the latest dated 2017 is 0.000 undetectable ;that is after being on high dose Glivec of 600mg daily.For a while we lost our molecular remission but have now regained  it in a very very deep manner.

It seems that there are limits to the degree to which the PCR test might detect the extent of the residual leukaemic cells in the bone marrow and that we will never be fully clear of the disease.There appear to be certain markers such as

log 3 reduction or 0.1 % or 1000 times smaller or 1 in a 1000,

log 4 reduction or 0.01% or 10,000 times smaller or 1 in 10,000

log 5 reduction is 0.001 or 100,000 times smaller  or 1 in 100,000

log 6 reduction is  I understand 0.000 or 1,000,000 times smaller or 1 in 1,000,000 but at this level Bcr/Abl transcripts are currently undetectable

So my query is are we only able to as far as log 5 with any reliability and so does log 6 exist

The other issue is that there will always be some residual levels of leukaemic cells in the bone marrow.The  meaning of  undetectable is 1 in 1 million residual cells.

One author suggested that there are 3 trillion cells in total in the bone marrow so in equivalence terms 1 in a million means that there are still one million residual cells in total in the marrow even if  a reading shows undetectable.

However it seems that if one maintains a score of undetectable one is unlikely to have a re -occurrence of the disease and unlikely ever to lose ones remission

Any comments?

John

 

l

Hi John,

My understanding is that MR5 is at about the dependable limits of current advanced kit. An old PCR machine in a lab might find a result "undetectable" which a modern one might find is only MR4. 

PCR has so many uses beyond what CML patients see it used for, so there's massive development ongoing. One development is ddPCR (droplet digital PCR) which seems to have the potential to be more sensitive to the qrtPCR (Quantitative Reverse Transcription PCR) that is currently the gold standard.

So I guess that, yes, we may in time see MR6 (and perhaps beyond?). In my opinion "undetectable" is only meaningful in the context of the quality of the test.

David.