International/European LeukemiaNet Working Group for FC in MDS has published consensus guidelines how the analysis should be performed and interpreted in the diagnostic work-up of MDS patients. For screening purposes, a mini-panel based on the so-called “Ogata score” can be applied including four parameters: percentage of CD34+ myeloid progenitor cells in bone marrow, frequency of B-cell related precursors within the CD34+ subset, CD45 expression on myeloid progenitors by comparison to lymphocytes, and orthogonal light scatter (side scatter, SSC) of granulocytes by comparison to lymphocytes. High scores (>2) are associated with high probability of MDS.
FCM percentages of CD34+ cells cannot replace the differential counts on smears. However, FCM may be informative if abnormal phenotypes of CD34+ cells are detected and some studies suggest that FCM CD34 counts may give better prognostic information than morphological counts.
Comprehensive immunophenotyping should include evaluation of aberrant features in progenitors, granulopoietic cells, monocytes and in erythropoietic compartment. Aberrant findings in at least three tested features comprising at least two cell compartments have been reported to be highly associated with MDS diagnosis. Multiple aberrant findings (especially in progenitors) conferred worse prognosis in several studies. Normalization of FCM results has been observed in patients responding to treatment.
Reporting FCM findings in MDS should be done in an integrated diagnostic report, together with morphological, cytogenetic and/or molecular findings. The report should include an interpretative comment stating whether the results are consistent with MDS, show limited number of changes seen in MDS or do not show MDS-related features.