Higher rate of central nervous system involvement by flow cytometry than morphology in acute lymphoblastic leukemia

Introduction: Central nervous system (CNS) involvement in acute lymphoblastic leukemia (ALL) is diagnosed traditionally by cytopathology (CP) of the cerebrospinal fluid (CSF). Role of flow cytometry (FC) to diagnose CNS involvement has not been extensively investigated. Methods: We aimed to detect CNS involvement in 42 ALL patients (33 B-ALL, nine T-ALL) at diagnosis by FC and comparing it with CP and to correlate it with known risk factors for CNS disease like Lactate dehydrogenase (LDH). A receiver operating characteristic curve was used to determine the cutoff of LDH to predict CSF involvement. For the analysis of categorical/quantitative variables, Fisher's exact test was used. For the analysis of continuous variables, Mann-Whitney test was used. A P value of <.05 was taken as significant. Results: CP and FC were positive in five (11.9%) and 11 patients (26.14%) respectively with FC detecting a significantly higher level of involvement (P=.001). All CP-positive cases were FC positive. A LDH value of >472U/L had a sensitivity of 61% and specificity of 62.5% for diagnosis of CSF involvement by FC. Conclusions: CSF FC detects CNS disease in ALL patients at diagnosis at a rate double than CP alone and is statistically associated with an elevated LDH level. It should be incorporated in the evaluation of CSF to detect CNS involvement.