The appearance of red blood cells (RBC) in urine
depends largely on the concentration of the specimen and the length of time the
red cells have been exposed.
Fresh red cells tend to have a red or yellow color (lower panel). Prolonged exposure results in a pale or colorless appearance as hemoglobin may be lost from the cells (upper panel). In fresh samples with S.G. of 1.010-1.020, RBC may retain the normal disc shape (upper panel). In more concentrated urines (>1.025), red cells tend to shrink and appear as small, crenated cells (lower panel). In more dilute samples, they tend to swell. At urine S.G. <1.008 and/or highly alkaline pH, red cell lysis is likely. Lysed red cells appear as very faint "ghosts", or may be virtually invisible. Red blood cells up to 5/HPF are commonly accepted as normal. Increased red cells in urine is termed hematuria, which can be due to hemorrhage, inflammation, necrosis, trauma, or neoplasia somewhere along the urinary tract (or urogenital tract in voided specimens). The method of collection must be considered in interpreting hematuria to aid in localizing the source, and because catheterization, cystocentesis, and manual compression can induce hemorrhage. |
Last Updated: January 16, 1996