Minimal residual disease (MRD) has become a crucial criterion for the risk stratification within modern protocols for the treatment of both childhood and adult acute lymphoblastic leukemia (ALL). According to the published data, levels of MRD in peripheral blood and bone marrow correlate well in T-ALL, whereas in B-cell precursor ALL the correlation is weak and MRD in blood is mostly more than one log lower than in the bone marrow.
Flow cytometry presumably reveals more positive results than "classical" microscopy.