Rehydration of air-dried smears with normal saline. Application in fluid cytology

Ninety fluid specimens (30 each of urine, ascitic and pleural fluid) were studied by preparing three comparable smears. One was air dried for Giemsa stain, one wet fixed in 95% ethanol and one dried on a hot plate at 37 degrees C, rehydrated in normal saline for 30 seconds and fixed in ethanol. The latter two were stained with Papanicolaou stain, and a comparison was made of the (1) retention of red blood cells, (2) retention of epithelial or mesothelial cells, and (3) cytologic preservation. The Giemsa-stained smear was used as a control for (1) and (2). Complete lysis of red blood cells was noted in the rehydration smears as compared with 70% red blood cell retention in the wet-fixed smears (P < .01). The rehydration smears retained 78% urothelial cells as compared with 55% in the wet-fixed smears (P < .01). For ascitic and pleural fluid the cell retention did not differ significantly. The wet-fixed smears scored better for overall cytologic preservation, but the difference was not significant. The rehydration smears showed a decrease in the chromaticity of staining, more flattened cell clusters and slight cell enlargement. The rehydration method was beneficial for urine and blood-stained body cavity fluids.