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Question about Pcr

Hi every one, it has been a long time and a long journey.

I come to you to ask one stupid question which makes me wondering about labo mistery.

I have totaly changed my way of thinking about cml now, that's life and I take it day by day. I am not really worried anymore.

My previous pcr showed an increase from 0.007 to 0.016 with 118749 copies.

My last one on august showed a decrease from 0.016 to 0.006 but with exactly the same amount of abl copies, number I have found on an old pcr on july 2018 too.

I have asked my labo which doesn't answer and my to onc who told me that this is totally normal and there is nothing to think about.

But I wanted to ask the cml community so I would like to know if this last pcr is valiable according that the result and calculation has been done by the head of the labo, in Lyon which is a top 10 in Europe.

I am curious to know if some of you have such pcr caracteristics, it is quite annoying. My last pcr is maybe not "true" or the previous one.

I have seen some papers on the web that abl cand be constant if it is the same patient in the same laboratory, but nothing more and I am not an expert.

I hope I have been enough precise, I begin to think that as cml become such a "usual" cancer for my hemato center and according to my onc, they don't really care and by facility took the same abl level. Or maybe it was to see if there was a true increase, I don't know.

Thanks in advance for your answer and sorry for my frenglish ;).

All of that is not only within the normal margin of error. 

You have gone from 7 in 100,000 to 16 in 100,100 then back to 6 in 100,000. It’s minuscule differences. Statistically insignificant. 

You’re doing great.

Thanks David for the quick answer!

That is true, it is tiny difference.

And what about the same abl copies between both pcr?

The number of ABL copies (or an other control gene) indicates the quality of the test. Ideally you want more than 100,000 for the most sensitivity - but you need a minimum of about 33,000 to test as deep as MR4.5.

Having the exact same number of ABL copies sounds fishy - perhaps a simple clerical error? One number copied and pasted into the next report? In either case, your PCRs are very low so there is no cause for any concern.


I habe noticed this beween my pcr of may and the last one on august.

More surprising again, I have noticed this number on july 0f 2018!

I have just phoned my labo that told me that yes it can arrive that there can be exactly the same number and there can't be any error because it is verified by 3 times and 3 or 4 different people.

Well, I am perplex anyway.

Croncretely, what is the consequence of taking exactly the same number and not the true by pasting it by error.

For example if abl 1 is lower or higher, does it have a big impact on calculation?

I have seen paper on the web on a french hemato center which told that they can take exactly the same number between two pcr if it is the same labo with the same patient.

I don't know, the only thing which I am fairly sure is that I am stable and I am not worried, just annoyed to see what happened and want to definitively understand pcr (despite the booklet)

The higher the number of ABL (or other control gene) the better the quality / resolution of the test. To detect down to MR5 you need 100,000 control gene assays. So the more, the better - it's that simple really.


Thanks David.

Finally, what can I conclude : is it a safe calculation?

Is the PCR correct or not, I am really confused.

If the abl 1 amount was higher, the pcr would be bader than 0.006%?

No. The PCR is a ratio. For example if there are 6 positive BCR-Abl assays our of 100,000 that is 0.006%. 3 in 50,000 would give the same result, as would 9 in 150,000 but it’s better to have the higher quality sample size. 

I used to receive my results with abl control and bcr-abl and the control was always different (sometimes 10x). I never understood the variations. Now my new test gives just the ratio directly.  

To use a fixed abl control to calculate the pcr is a weird approximation, especially if the blood sample has to travel far.

The control gene sample size changes due to the quality of the test. It’s not directly controllable by the lab.

Temperature, age of the sample and all sorts of factors play into it.

I don’t buy that two tests actually will have the same number of control assays. It’s statistically highly, highly unlikely. If three tests it’s virtually impossible. 

Ok, so that is inducing that my pcr is not valide if I understand. So I will have to wait for 3 months to see if all is ok.

I think wIth such a low PCR result you have nothing to worry about. It’s a bit unusuaL. If your results were 0.8% or something you would need to get to the bottom of it, but with your excellent and optimal results it is all OK..

I call another time the lab to know exactly what was going on and had the head who is camping on her arguments.

She told me a bit more, they took exactly the same amount of dna (not sure of the name) at the nearest nanoliter and surely lower and was formal to say that having the same abl 1 level was totally normal considering the stricly same quantity putted in a pcr machine.

Honestly, I will have a talk with my onc and ask to watch on this level. My hemato is the best I can have but people in the lab are not ok in the way of explaining

I think I have lost a precious time and would like to see in another lab but it is strictly impossible.