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PCR / FISH results
hi kenny,
go to FAQ/Glossary page where you will find an explanation of the different tests such as cytogenetic; FISH and PCR.
PCR is a very accurate and sensitive test which can detect very low (molecular)levels of disease, even when there is none evident in the peripheral blood.
FISH tests around 200 cells and is not as sensitive as PCR , it also does have a percentage of false pos/neg results, that you must take in to acount.
normally when you have a CCR or complete cytogenetic response to glivec it means that your level of disease is not detectable by FISH....i.e ph+ cells cannot be seen under the microscope as they are at levels at around or under 1.5-2%.... therefore PCR is used to detect the levels of bcr/abl in your marrow.
it is very important to get this test done at a lab that conforms to the same standards of procedure as other labs.
PCR tests are sensitive to all sorts of things and can easily be contaminated.
so 3 tests will give you a more accurate picture or 'trend' than just one.
hope this is more helpful than confusing!....
best wishes,
sandy
Thanks for that Sandy - still confused as to why 15%+ by FISH does not roughly equate to 15%+ by PCR. The PCR just seems to be a more sensitive test. I think it may be something to do with the 'baseline comparator' ie for FISH it's normal cells and for PCR it's something else...
I got a 15% result back for PCR after 3.5 months - they messed up the FISH test for some reason so still waiting for that one.
Anyway - did I read somewhere that there was going to be a conference in Glasgow this year?
Regards,
Kenny
hi kenny....... quantative PCR measures the % of bcr/abl present in the marrow.
FISH is only sensitive to around 200 cells and marks PH+ cells with a flourescent dye which makes the abnormal cell visible to the naked eye... thus they can be seen down the microscope.
if your bcr/abl percentage is below 1.5% -2% by PCR then ph+ cells will not be visible in sample (peripheral blood and marrow sample)and your FISH test should be negative however this is not often the case as with FISH there is a considerable false pos/neg percentage to take into account... so the results from both tests do not generally coincide.
the housekeeping gene or 'baseline comparitor' used in pcr is the normal ABL gene..(as opposed to the abnormal bcr/abl gene).
so the two tests are not the same. PCR in some labs can test a very large number of cells, whereas FISH only tests up to 200 and is a lab culture.
if your last PCR shows 15% then you should wait for the next one to compare it with.... PCR is the MOST sensitive test available and is generally what those with CompleteCR or MajorCR rely on.
i also heard that Glasgow was the next venue for the UK conf. but i have also heard that it may well be Newcastle in the north east.
best wishes,
sandy
sandy C ;o)
Hi Kenny,
Let me try and explain it.
15% CML cells is always 15%.
You need to know the number of cells tested and the number of CML cells found in order to calculate the %.
A FISH test usually looks at 200 cells. If 30 of these cells are CML cells then you have 15% leukemic cells in your body.
A BMA usually looks at 25 cells. If 4 of these were CML cells then you would have 16% CML cells in your body.
Now for the PCR calculation. Big problem. They never tell you how many cells they look at nor do they tell you how many of these cells are CML cells. So you cannot do the calculation.
The reason they do the PCR test is because it is a very sensitive test and once you have attained 0 by FISH test you need some other test to see how well you are doing.
There are 2 types of PCR tests (qualitative and quantitative) that are done. The qualitative PCR test simply reports YES or NO. A % is not reported. This is a handy test if they tell you how many cells they looked at. Some labs look at 10,000 cells and other labs will look at 1,000,000 cells.
The quantitative PCR test reports in 2 ways. The first way will tell you how well you have done compared to where you were when you were first diagnosed with CML. Since they normally don't do a PCR when you are first diagnosed, they guess at what that starting number is. (This is yet a further comlication for us mortals.) The results are then reported as log reduction from the value at your initial diagnosis. An excellent result to have will be a 3 log reduction. This means that the number of CML cells in your body are 1000 times less than you had when first diagnosed. (The assumption is that you were 100% CML positive at diagnosis.
The second way that the PCR test is reported is as a %. This is the part that is very confusing. They don't tell you the number of cells that they looked at, nor do they tell you how many were CML cells so you can't do the calculation. In fact, it is not cells that they look at but parts of a cell. It is a ratio of the bcr-abl gene to a housekeeping gene ... blah blah blah.
All this is to tell you that 15% via a PCR test is not what us ordinary mortals think it is or should be.
Zavie
Zavie Miller (age 68)
Ottawa, Canada, dxd AUG/99
INF OCT/99 to FEB/00, CHF
Gleevec since MAR/27/01 (400 mg)
CCR SEP/01. #102 in Zero Club
2.8 log reduction Sep/05
3.0 log reduction Jan/06
> 4 log reduction Nov/06
zmiller@sympatico.ca