- MRD is defined as patients meeting the criteria for CR above, but with residual disease measured by a quantitative PCR, or by flow or by deep-sequencing of the IgH rearrangements . The assay from blood and/or bone marrow defines MRD by qPCR as a cycle threshold (CT) that is at least 1 CT value < than the lowest CT value from the background. Outside laboratory tests may suffice for this assessment at the discretion of the Principal Investigator.