Advances in the diagnosis and treatment of acute myeloid leukemia (AML) have resulted in high overall rates of complete remission (CR) in a high percentage of patients. CR is currently defined by a combination of clinical and microscopic data and is heavily dependent on the enumeration of blasts in post-induction bone marrow. Studies have shown that this method is less than optimal for prediction of relapse. Minimal residual disease (MRD), refers to the presence of leukemic cells at levels too low to detect by conventional methods and correlates better with prediction of relapse.
High sensitivity flow cytometry can reliably detect MRD in AML with a sensitivity of approximately 0.1 - 0.01%. Several studies have shown that high sensitivity flow MRD detection is strongly correlated with survival and risk of relapse. High sensitivity flow can be used in virtually all AML patients regardless of age or cytogenetic and molecular findings. Many AML patients have abnormal expression of antigens, termed leukemia-associated immunophenotypes, which are useful for diagnosis of residual disease. AML blasts can also be identified by their deviation from the normal antigen expression patters seen in bone marrow, commonly know as difference from normal. The importance of MRD status lies in its ability to provide an objective assessment of treatment response to guide subsequent treatment decisions. Consequently, it is best used after treatment and obtaining a morphological remission.