RBC in urine

Red blood cells (RBC) iare reported semiquantitatively as number seen per high power field (HPF):

none seen; <5, 5-20, 20-100, or >100/HPF.

Interpretation: Up to 5 RBC/HPF generally are considered acceptable for "normal" urine.

Upper: RBC in fresh urine are red with a smooth texture. In dog urine, they are slightly biconcave (arrows). Lower: RBCs in stored urine can crenate taking on a spiky appearance (arrows). The colorless grainy round cells in amongst the RBC are WBC in this urine from a cat with cystitis.

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.

Identification: The appearance of red blood cells in urine depends largely on the concentration of the specimen and the length of time the red cells have been exposed.

In fresh urine, RBCs are round smooth cells and are slightly red-tinged (from hemoglobin). In fresh samples with specific gravity of 1.010-1.020, RBC may retain their normal disc shape, particularly in dogs. In more concentrated urines (>1.025), red cells lose their smooth texture, tend to shrink and appear as small, crenated cells (see image to the right). In more dilute samples, they tend to swell. At urine specific gravity <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.


Cornell University