1: Cellular Elements
- Page ID
- 69936
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1.1 Red Blood Cells (RBC)
Morphology: Normal RBC vary from 6-9 micrometers in size. They are round and biconcave. In hypertonic urine the cells appear crenated; shrunken with small spikes. In hypotonic urine the cells will increase in size and appear colorless. Dysmorphic RBC can arise from glomerular diseases and will appear misshaped, fragmented and/or have protrusions. “Ghost cells” is a term used to describe RBCs that have lysed leaving behind their outer membrane.
Disease correlation and clinical significance: Pathological causes of RBCs in urine include, glomerular membrane damage/disease, urinary tract infections, kidney stones, and trauma to kidneys. Non-pathological causes to RBCs are typically due to menstrual contamination.
Helpful Hints: RBC, yeast and oil droplets look similar and need to be differentiated. To distinguish between RBC and yeast, acetic acid (1:1) can be added to urine sediment. RBC will lyse in the presence of acetic acid but yeast will remain intact. To distinguish RBC from oil droplets, use lipid stains such as Oil Red O or Sudan III.
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1.2 White Blood Cells (WBC)
Morphology: WBCs are 10-14 micrometers in size. The most common WBC seen in urine is a neutrophil. Thus, most WBCs in the urine will appear granular, except for lymphocytes and monocytes.
Disease correlation and clinical significance: Pathological causes of WBCs in urine include urinary tract infections, inflammation and glomerular diseases. Presence of eosinophils in urine are associated with interstitial nephritis.
Helpful Hints: When distinguishing WBC from RBC, WBCs look more granular and “fuzzy” compared to RBCs. Also note the size difference, WBCs are typically larger than RBCs.
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1.3 Squamous Epithelial Cells
Morphology: Squamous cells are the largest of the cells at 50-100 micrometers. The cell has an irregular shape and consists of a nucleus the size of a large RBC. The edges of the cell membrane are often folded, irregular or wrinkled in appearance. Squamous epithelial cells originate from the lower urethra and outer mucosa of the genitalia.
Disease correlation and clinical significance: No pathological significance.
Helpful Hints: When squamous cells are folded they can resemble a cast. To differentiate between a cast and a squamous cell look for the nucleus, a cast does not have a nucleus.
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1.4 Transitional Epithelial Cells
Morphology: The size of a transitional epithelial cell is smaller than a squamous cell but larger than a RTE cell and WBC. They typically have a centralized nucleus and can come in various shapes such as oval, pear, spherical and caudate. The boarder of a transitional epithelial cell membrane is more defined and has higher contrast than the boarder of a squamous cell. Transitional epithelial cells originate from the upper urethra, bladder, ureter and renal pelvis.
Disease correlation and clinical significance: Pathological causes of transitional epithelial cells in urine include, infection, kidney stones, inflammation, and bladder cancer. Non-pathological causes for transitional epithelial cells in urine are typically due to catheterization.
Helpful Hints: To distinguish from squamous cells, look for the rounded, more defined cell membrane and smaller size.
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1.5 Renal Tubule Epithelial Cells (RTE)
Morphology: Renal tubule epithelial cells (RTE) are smaller than squamous and transitional epithelial cells but typically larger than WBCs. They come in various shapes including, round, oval, cuboidal and oblong. Many forms have an eccentric nucleus, with less cytoplasm than a transitional or squamous epithelial cell. RTE cells originate from the tubules within the nephron; proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting duct.
Disease correlation and clinical significance: Pathogenic causes of RTE cells in the urine include damage to renal tubules, ischemic events in the nephron and viral infections.
Helpful Hints: Use size, amount of cytoplasm, and position of nucleus to help differentiate an RTE from a transitional epithelial cell and squamous epithelial cell. Typically, RTE cells are the smallest of the epithelial cells, have less cytoplasm and have an eccentric nucleus. Some RTE cells have a flat edge on their outer membrane which can help to distinguish them from transitional cells.
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1.6 Oval Fat Bodies
Morphology: Oval fat bodies are RTE cells that contain fat droplets. Due to the cells containing fat, oval fat bodies may demonstrate Maltese cross formation under a polarizing microscope. The fat droplets cause oval fat bodies to be highly refractile.
Disease correlation and clinical significance: Pathogenic causes of oval fat bodies in urine include nephrotic syndrome and renal tubule damage.
Helpful Hints: A specimen that contains oval fat bodies will typically contain free floating fat droplets. If oval fat bodies are suspected use lipid stains or polarizing microscopy to confirm.
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1.6.A Fat Droplets
Fat droplets are not a cellular elements but can be seen in conjugation with Oval Fat Bodies. Fat droplets are lipids composed of either triglycerides, neutral fats or cholesterol, or a combination of these lipids. Pathologic causes for fat droplets in urine includes nephrotic syndrome and glomerular damage. Fat droplets appear round, vary in size and are highly refractile. Fat droplets look similar to RBCs, to differentiate use lipid stains such as Oil Red O or Sudan III.
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