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About the qRT-PCR test
This section provides an overview of the quantitative Reverse Transcriptase Polymerase Chain Reaction (qRT-PCR) test. It includes a description of the qRT-PCR International Standardisation (I.S.) project within the context of the recently updated (2013) ELNet Recommendations and NCCN Treatment Guidelines for the treatment and management of Ph+CML based on molecular testing by qRT-PCRI.S..
For simplicity the test is referred to as q-PCR throughout. We hope these pages will also serve as an exemplar in a healthcare environment where patients face a lifetime on therapy, enabling an in-depth understanding, not just of the disease and its current treatments, including those in development, but also test methodologies used to monitor responses to therapy. This primer has been developed following a suggestion from patient self-educators as a way to encourage a better understanding of q-PCR testing. The draft was further developed by Sandy Craine who is the author of the text on behalf of the CML Support Group.
So what is the test?
At diagnosis, virtually every white cell in a blood or marrow sample will be leukaemic (Ph+) so the test result should, in theory, be 100% Ph+. However, because there are higher levels of Ph+ cells present at diagnosis, q-PCR testing is not accurate, which is why Ph positivity varies between 50% and 100%. This test may be used to establish a baseline value of Ph+ cells at diagnosis.
After the start of therapy q-PCR is used at specific time points after cytogenetic/FISH tests. Once tests show that the Ph+ cell population has reduced to less than 10%, q-PCR testing can more accurately quantify the amount of residual disease left in the marrow.
The goal of TKI therapy is to reduce the abnormal BCR-ABL1 gene to a deep molecular level, preferably to at least 0.1% (MMR/MR3).
During the first 3, 6, 9 and 12 months of therapy Ph+ cells should reduce significantly. When the level of Ph+ cells falls below 1% q-PCR testing is extremely accurate and will be used to monitor the stability of a molecular response. Under ideal conditions, this test can detect 1 Ph+ cell in every 100,000 cells, although more commonly it detects 1 Ph+ cell in every 10,000.