Interpretation of atypical patterns encountered when using a flow cytometry–based method to detect residual leukocytes in leukoreduced red blood cell components

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Abstract
Background Universal leukoreduction of blood components is becoming the standard of care. Flow cytometry methods are being used for quality control of the leukoreduction process. Methods We provide an atlas of atypical flow cytograms generated by a commercial LeucoCOUNT™ assay that was used to enumerate residual leukocytes in leukoreduced red blood cell components. Numeric results are derived from a flow cytogram generated by the assay. Results Three types of atypical flow cytogram patterns were observed during process validation or routine quality control of leukoreduced red blood cell components. (a) Fixation artifact: Fixation of control or test samples can alter the staining intensity compared with fresh cells. (b) “Rain” pattern: Flow cytometry methods count slightly damaged leukocytes not removed during leukoreduction. Slightly damaged leukocytes appear on a flow cytogram like “rain” falling from a well‐defined “cloud” of intact residual leukocytes. Discrepancies between automated flow cytometry results and subjective manual counting methods can occur. (c) Autofluorescence‐debris pattern: Cell debris and age‐related changes in the sample can cause shifts in the fluorescence staining pattern, resulting in erroneous test results. Conclusion Review of flow cytograms is essential for accurate reporting of flow cytometry–based methods for enumerating residual leukocytes in leukoreduced blood components. Cytometry (Clin. Cytometry) 50:254–260, 2002.