Chemical preservation of urine sediment for phase-contrast microscopic examination

A major difficulty in diagnostic urinary microscopy is the need to observe a freshly passed urine specimen. This study illustrates the use of glutaraldehyde (GA) and formaldehyde (FA) to preserve urinary sediment for diagnostic microscopy. GA and FA in whole urine cause a precipitate to form if there is a trace or more of proteinuria. This can be eliminated by centrifugation and fixation of urine sediment. Red blood cells (RBC) and casts are adequately preserved for diagnostic microscopy for at least 3 months. However, subtle changes in RBC morphology consisting of hexagonal distortion and wrinkling of cell margins are seen in some cells. White blood cells (WBC) are less reliably preserved. Diagnostic phase-contrast microscopy can be performed on urine sediment stored at room temperature for up to 3 months after fixation with GA or FA.