Normal BCR-ABL1 Test Result
A normal BCR-ABL1 test result is undetectable BCR-ABL1 transcripts, reported as "BCR-ABL1 not detected" or "negative." This indicates the absence of the Philadelphia chromosome-associated fusion gene that characterizes chronic myeloid leukemia (CML).
Understanding BCR-ABL1 Testing Context
The BCR-ABL1 test detects the fusion gene resulting from the reciprocal translocation t(9;22)(q34;q11.2), which is the hallmark of CML 1. In healthy individuals without CML or Philadelphia chromosome-positive acute lymphoblastic leukemia, this fusion gene should be completely absent 1.
Reporting Standards for Normal Results
- In individuals without CML: The result should simply state "BCR-ABL1 not detected" or "negative" 1
- No quantitative value is assigned when the fusion transcript is absent in screening scenarios 1
Important Distinction: Monitoring vs. Screening
The detailed molecular response (MR) classifications you may encounter—such as MR4, MR4.5, or MR5—apply only to CML patients undergoing treatment monitoring, not to normal screening results 2:
- MR4: ≤0.01% BCR-ABL1 on International Scale (IS) with adequate reference gene transcripts 2
- MR4.5: ≤0.0032% BCR-ABL1 IS or undetectable disease with ≥32,000 ABL1 transcripts 2
- MR5: ≤0.001% BCR-ABL1 IS or undetectable disease with ≥100,000 ABL1 transcripts 2
These classifications represent deep molecular responses in treated CML patients, not normal baseline values 2.
Technical Considerations
- Reference gene requirements (minimum 10,000 ABL1 or 24,000 GUSB transcripts per replicate) apply only when assessing molecular response depth in CML patients 2
- Limit of detection: Modern qRT-PCR assays can detect as few as 3 BCR-ABL1 copies with 95% confidence, but this sensitivity is relevant only for monitoring residual disease 2
Clinical Pitfall
Do not confuse "undetectable BCR-ABL1" in a treated CML patient (indicating deep molecular response) with a normal screening result in someone without CML. The former requires specific reference gene thresholds and International Scale standardization 2, while the latter is simply a negative test 1.