Red blood cells
White blood cells
A variety of cells can frequently be seen in the urine, including some red blood cells, white blood cells and epithelial cells originating from the kidneys or lower urogenital tract; such a finding is not considered to be pathologic.
| Red blood cells
Red blood cells occur in the urine in case of vascular lesion, renal disease, or lower urogenital tract disease. Red blood cells count determination is important in the diagnosis of renal disease as well as in the follow-up of treatment success. When a woman's urine sample is being examined, it is important to know if she is having menstruation, or is in the immediate pre- or postmenstruation period, thus to avoid possible misinterpretation of positive result due to urine sample contamination with menstrual blood. Red blood cells in the urine can be of renal or subrenal origin. Normal 'eumorphic' red blood cells are of subrenal origin and their source is in the draining part of urinary tract.
Renal dysmorphic red blood cells originate from kidney parenchyma (e.g., in glomerulonephritis) and exhibit morphologic changes (serration, spurs, deformities, fragments, etc.). The presence of more than 30% of dysmorphic red blood cells in the urine points to their renal origin.
Turbid urine or urine of a red-brown color are due to the presence of a large number of red blood cells in the urine. Red blood cells are round, thin, sharply contoured, biconcave, pale-yellow, non-nucleated and nongranular disks.
Red blood cells frequently change color and shape due to variability in substance concentration and pH.
| White blood cells
White blood cells enter the urinary tract through glomeruli or via ameboid migration among tubular cells. On light microscopy, a majority of white blood cells are identified as segmented neutrophils. Special urinary sediment staining methods are used to identify lymphocytes, plasma cells and eosinophils.
White blood cells are round cells of a varying size ( ~12 µ), their granular structure being markedly seen in acidic urine. In alkaline urine, white blood cells swell up and their contours become indistinct. The white blood cells nucleus can be round or split (segmented), and is frequently covered with granules, thus it may be difficult to see. The nucleus is centrally located. The cytoplasm is markedly inhomogeneous, while the granules within the cytoplasm may vibrate (Brownian movement).
Epithelial cells of various form and size are found in the urine. They all are nucleated cells, many of them granular. The size and form of epithelial cells primarily depend on the site of their origin and on urine pH. Although quite variegated, the appearance of epithelial cells is not indicative of the urinary tract segment they originate from. Morphologically, these cells are classified into three groups:
renal or tubular epithelial cells (round cells of renal epithelium),
squamous epithelial cells (cells of external genitalia), and
transitional epithelial cells (of round, pear-shaped or spindle-shaped).
Squamous epithelium is exclusively found in the urinary sediment of a healthy individual. A finding of round renal cells is most important for the diagnosis of renal disease.
| Squamous epithelial cells
Scalelike epithelial cells coat distal parts of the lower urinary tract and genital organs in women. These are largest epithelial cells that can be found in the urine. Squamous epithelial cells are the largest cells found in urinary sediment (40-60 µm). They are of a polygonal shape, with small, centrally located nuclei and large cytoplasm. One or more cell angles are rounded.
| Transitional epithelial cells
Transitional epithelial cells may be round, pear-shaped, or spindle-shaped (elongated cells, flagellate cells). They have round or oval nuclei that are relatively large and centered. The cytoplasmic edges of transitional epithelial cells are tight and transparent.
| Renal or tubular epithelial cells
Old or diseased tubular epithelial cells coating the nephron are continuously removed by the urine and replaced by new cells. In normal urine, less than 2 cells/HPF are found. The presence of more than 2 tubular epithelial cells per HPF indicates an active lesion of renal tubules.
Renal epithelial cells are small round cells with a high nuclear/cytoplasmic ratio and large, marked nuclei. They are finely granulated, and somewhat larger than white blood cells. The cell nucleus is round, frequently eccentrically located, of 20-30 µm in size (10-60 µm in diameter). In size, they are greater than white blood cells. In a preparation stained according to Sternheimer-Malbin, the nucleus is dark-red, and the cytoplasm is pink to light-blue.