Correlation of MRD levels assessed by quantitative PCR and flow cytometry. In 254 samples from 30 patients, quantification of CLL cells (expressed in logarithmic scale) measured by quantitative PCR and flow cytometry correlated well (r = 0.826, P < .001). The sensitivity achieved by each of these techniques are labeled with dotted lines. MRD⁺ samples (n = 49) by qPCR and negative by flow cytometry and those MRD^– samples (n = 8) by qPCR but positive by flow cytometry are depicted out of the dotted lines. MRD^– samples (n = 86) by the 2 techniques are shown below and to the right of the dotted lines.