<p>Acute myeloid leukemia (AML) is an aggressive hematologic malignancy where chemoresistance, particularly to daunorubicin (DNR), frequently leads to treatment failure and relapse. Current resistance prediction methods are often slow and inaccessible in clinical settings, delaying crucial treatment adjustments. There is an urgent need for rapid, reliable, and clinically accessible diagnostic tools to identify DNR resistance early, enabling personalized therapeutic strategies and improving patient outcomes. To address this problem, we developed a rapid flow cytometric assay to detect reduced intracellular DNR accumulation, a marker of drug resistance. This was complemented by FTIR spectroscopy, confocal microscopy, and proteomic profiling to validate findings and explore underlying mechanisms in drug-resistant and sensitive cells. The flow cytometry method demonstrated that the novel Sensitivity Index (S-index) accurately predicts DNR resistance after short drug exposure and correlates strongly with IC₅₀ values. Complementary FTIR and confocal microscopy revealed distinct biochemical and structural differences between resistant and sensitive cells. Proteomic analysis suggests that increased drug metabolism contributes to DNR resistance, supporting the flow cytometry data. In summary, our findings demonstrate that flow cytometry provides a reliable and clinically accessible tool for targeted diagnostics, crucial for optimizing patient-specific treatment strategies based on rapid assessment of daunorubicin resistance in AML.</p>