RBCs remaining in supernatant and RBC morphology after urinary sediment preparation

Abstract

Several factors may cause errors in the urinary sediment test, including centrifuge operation and supernatant removal. Previously, we reported a discrepancy between red blood cell (RBC) counts from flow cytometric analyses of noncentrifuged urine samples and urinary sediments after centrifugal separation, which was identified by basic evaluation at the entrance of the automated urine particle analyzer. To investigate the cause of this discrepancy, we examined RBCs remaining in the su2pernatant and RBC morphology after urinary sediment preparation. A significant amount of RBCs was observed to remain in the supernatant after centrifugal separation, leading to the above discrepancy. In addition, we found that RBCs that were judged “mixed” or “dysmorphic” by flow cytometric analysis were more likely to remain in the supernatant compared with RBCs that were judged “isomorphic”.