Relationship between the number of CLL cells detected in peripheral blood and the degree of bone marrow infiltration in patients with CLL who received stem cell transplants. Paired peripheral blood and bone marrow were analyzed in 103 samples by qPCR (A) and in 109 samples by flow cytometry (B). A good correlation was observed between peripheral blood and bone marrow levels assessed by qPCR and flow cytometry, with correlation coefficients of 0.786 and 0.856, respectively (P < .001). Samples with an MRD amount differing more than one logarithm between both sites are depicted out of the dashed lines.