OVERVIEW
Standard RT-PCR is reserved for patients not harbouring a transcript variant amenable to monitoring via QRT-PCR. Sensitivity of this assay has not been specifically determined and likely varies between transcript variants. RT-PCR is generally first initiated by the laboratory in response to a negative QRT-PCR test on a patient with demonstrated t(9;22). Subsequent to the formal identification of the transcript variant in question, follow-up monitoring is performed by this method. Invariably, results are reported qualitatively as either positive or negative for the presence of the transcript variant in question.
INDICATION
1. Laboratory initiated reflex test in patients with demonstrated t(9;22) positive disease (diagnosis either by FISH or karyotype) and a negative QRT-PCR test.
2. Follow-up test for monitoring of minimal residual disease (or measurable residual disease).
The following testing interval applies to follow-up testing. Specimens received by the laboratory outside of these intervals, without prior consultation, will be discarded.
- Patients treated with a TKI
- Every three months, indefinitely
- Patients who discontinue treatment for a limited time due to planned (or unplanned) events
- Every month, until resumption of therapy (to a maximum of one year)
- After one year, monitoring transitions to every three months indefinitely
- Post-transplant patients not being treated with a TKI
- Monitoring is at the discretion of the treating physician.
- For any scenario not covered above, please contact the laboratory in order to come to a mutually agreeable testing interval.
REFERRAL
Any treating physician.
TEST REQUIREMENTS
- Completed CGL Myeloid Testing requisition form [link]
- One of the following specimens (please see our Guidelines/Policies for Samples and Transport)
Preferred:
- 20mL Peripheral Blood in EDTA tubes (purple top)
Alternative:
- 5mL Bone marrow aspirate in EDTA tubes (purple top)
- Peripheral blood derived white blood cells fixed in methanol/acetic acid (residual cytogenetic specimen)
- Bone marrow specimen fixed in methanol/acetic acid (residual cytogenetic specimen)
Figure 1: Requisition entries for RT-PCR testing of CML patients. Note that RT-PCR is not a routinely orderable test at diagnosis.
TRANSPORT
Click here for guidelines on transporting specimens.
METHOD
Total RNA is extracted from the submitted specimen and converted to cDNA (random primed reverse transcription – RT) for subsequent PCR. Both the BCR::ABL1 and ABL1 RT-PCR products are visualized (and sized) via electrophoresis (TapeStation) and reported qualitatively (e.g. Positive, Negative, etc).
CLINICAL UTILITY
At diagnosis, RT-PCR positivity is equivalent to the identification of t(9;22) by FISH. Subsequent MRD monitoring will follow the breakpoint identified by this test.
TURN AROUND TIME
Results are reported within ten working days from receipt of specimen and completed requisition form.