Epithelial cells in urine

1.  Epithelial cells 

Microscopic appearance- The three major types of epithelial cells found in urine are squamous, transitional and renal tubular cells

Squamous epithelial cells - In urine, these cells are large, flat cells with abundant cytoplasm and small round nucleus. The distal one third of the urethra and female vagina is lined with squamous epithelial cells. 

Transitional or urethral epithelial cells-- These cells line the urinary tract from the proximal two thirds of the urethra up to the renal pelvis. They are round or pear shaped, their size varying from 40200 um. The nucleus is centrally located.

Renal tubular epithelial cells- These cells forma single layer epithelial lining from the proximal and distal convoluted tubules and the cells lining the collecting ducts up to the pelvis of the kidney. Identification in unstained preparation is difficult. The cells lining the convoluted tubules occur singly. 

They are oval cells measuring 14-60 um with characteristic coarsely granular cytoplasm with one or two dense nuclei. Epithelial cells from the collecting ducts measure 12-20um, are cuboidal in shape and contain a large nucleus which is usually eccentric.
 
 Some renal epithelial cells may contain fat bodies in their cytoplasm. Their presence is clinically significant and should be reported. These fat containing cells may be associated with fat globules of various sizes. Occasionally renal epithelial cells may also contain haemosiderin pigmentor inclusion bodies of viruses such ascytomegalovirus. 


The presence of the above structures in a wet preparation should be confirmed with appropriate staining (Sudan Black B for fat, Prussian blue for haemosiderin, Papnicolaou for inclusion bodies).

 Clinical significance:-  A small number of epithelial cells in urine is a normal finding due to sloughing of ageing cells. Increased number of  squamous epithelial cells in female urine is not significant and is due to contamination of urine by vaginal secretions. A presence of large clumps or sheets of transitional epithelial cells is either due to instrumentation such as catheterisation or due to urinary tract lesions or tumours.

The renal epithelial cells from proximal or distal convoluted tubules are seen in large numbers in acute tubular necrosis and toxicity due to certain drugs and metals. The increased number of collecting duct epithelial cells is seen in acute glomerulonephritis and malignancy.