The MRDx Test utilizes quantitative, real-time reverse transcription polymerase chain reaction (RT-qPCR) for BCR-ABL and ABL quantitation. The rapid, one-step protocol allows for both reverse transcription and quantitative PCR reactions to be performed in the same well. This provide the advantage of increase sensitivity while limiting experimental variables and also reducing time and cost. The MRDx BCR-ABL Test uses BCR-ABL and ABL standard curves to determine BCR-ABL and ABL copy numbers. The assay has been harmonized to the WHO primary standards for determination of Major Molecular Response (MMR) levels based on the International Scale (IS). Major Molecular Response (MMR) or MR3, defined as greater than or equal to a 3-log reduction in the ration of BCR-ABL/ABL from a standardized baseline value, reflects a patient's response to treatment. In addition, the MRDx BCR-ABL Test includes MR4.5 to enable quantification to 0.0032% IS, which is greater than a 4-log reduction, important for treatment discontinuation and for monitoring of treatment-free remission.