Cells

Urine is a hostile environment for cells since they encounter abnormal osmotic pressures, pH changes, and exposure to toxic metabolites. For these reasons, post-collection delay of examination should be minimized. If delay is unavoidable, refrigeration will slow degeneration of cells.

For routine purposes, cells are examined as unstained wet-mounts of sedimented urine. Under some circumstances, air-dried smears are prepared and stained with hematologic stains for cytologic assessment. This is indicated if neoplasia (e.g. transitional cell carcinoma) is suspected.

Red blood cells and leukocytes are quantified as cells/HPF (High Power Field - 40x objective). Other cell types are usually subjectively listed as "few, moderate, or many" (based on low power).

Cells Information

RBC

Fat droplets

Classified as number per HPF: none seen, <5, 5-20, 20-100, or >100

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

Round, slightly red-tinged, smooth textured cells, which may be biconcave in fresh urine

May be spiky (crenated) in stored urine

May lyse in very alkaline or dilute (USG < 1.008) urine

Compared to fat droplets: RBC are more uniform and red-tinged versus fat droplets are more variable in shape, slightly greenish-tinged (or refractile), have a darker edge, are more globular shape (this can be visualized when you focus up and down) and usually float to the top of the coverslip (thus when fat droplets are in focus, the other urine constituents are out of focus - see lower panel on left)

WBC

Classified as number per HPF: none seen, <5, 5-20, 20-100, or >100

Normal: Up to 5 WBC/HPF generally are considered acceptable for "normal" urine - these are normally segmented neutrophils

Round, colorless cells with a grainy texture (see upper panel on left - bacterial rods are also visible in the background), may see nuclei of cells

May lyse in very alkaline or dilute (USG < 1.008) urine

Compared to RBC: WBC are more grainy and larger

Compared to transitional epithelial cells: WBC are smaller with rounder borders than epithelial cells which vary in size, are less grainy and usually have eccentric nuclei (when visible) (see arrowed cell on lower panel on left which is from the same urine as the upper panel)

Transitional epithelial cells From renal pelvis, ureters, urinary bladder and/or urethra

Variable size and shape (depends on origin): round or polygonal, pear-shaped, caudate (pelvis), tailed, spindle, may develop refractile, fatty inclusions with storage

Compared to WBC: WBC are smaller and more uniformly round

Compared to squamous epithelial cells: Transitional cells are smaller with rounder (not as angular) borders

Can be seen in normal urine (few in samples collected by mid-stream catch or cystocentesis, more in catheterized specimens due to catheter-induced sloughing) as single cells or small clusters, more may exfoliate with inflammation

Difficult to distinguish from neoplastic cells - this requires urine cytology

Squamous epithelial cells Largest cell in urine (image on the left was taken at lower magnification than the other images on this page)

Thin, flat cells, with angular border, anuclear or small central nuclues, present as single cells (shown on left) or in variably-sized clusters

Represent contamination (from skin, genital tract, prepuce in male dogs) in voided urine or may reflect squamous metaplasia of prostate (from exogenous estrogen or an estrogen-secreting Sertoli cell tumor) especially if in large numbers

Neoplasia May exfoliate into urine in animals with tumors of the genitourinary tract

Most common type is transitional cell carcinoma (TCC) - arises in urinary bladder, urethra (including prostatic urethra in dogs). Rarely, lymphomas and renal carcinomas can also be observed in urine sediments

Compared to normal transitional epithelial cells: Display cytologic criteria of malignancy such as variation in cell and nuclear size (see upper panel on left). Frequently exfoliate as variably sized irregular clusters.

Abnormal features may be difficult to discern in unstained urine sediments, particularly in stored samples where nuclei and cells swell with time. For instance, compare the cluster of neoplastic transitional epithelial cells (arrow in lower panel on left) to the normal transitional epithelial cells demonstrated in the table above. The cells look quite similar. In these cases, cytologic examination of a Wright's (or Diff-quik-stained) urine sediment is the preferred method of diagnosis

Common crystals

Illustrated below is a table of common crystals that can be seen in urine, along with the pH of the urine in which these crystals usually precipitate and some additional information about the crystals. Note, that this is not an exhaustive list and the pictures are not necessarily to scale (e.g. bilirubin crystals are usually quite small). For more detailed information and other images of the crystals, please refer to the urine crystal page in our routine urinalysis section.

Crystal pH Information

Ammonium biurate

Usually neutral to acidic: pH ≤ 7

Brown, spherical to irregular crystals ("thorny" apple)

Common in Dalmations, English bulldogs

In other breeds of dogs or cats suggests liver dysfunction and portosystemic shunting

May occur with amorphous urates or sodium urate (needles or prisms)

Amorphous

Phosphates: pH ≥ 7

Urates: pH ≤ 7

Small, irregularly shaped crystals

Can be of different composition (urates, xanthine, phosphate) depending on pH.

Can be seen in healthy animals

Mimic bacterial cocci - perform a gram stain to differentiate

Bilirubin

Acidic: pH < 7

Small needle-like to granular yellow or yellow-brown crystals

Indicates bilirubinuria due to conjugated (direct) bilirubin

Bilirubinuria can be normal in dogs but is abnormal in other species.

Calcium carbonate Usually alkaline: pH ≥ 7

Spherical to irregular (rhomboid, dumb-bell, ovoid) yellow to colorless crystals. Spherical forms have radial striations.

Normal in horses, guinea pigs

Not normally seen in dogs, cats or ruminants.

Calcium oxalate dihydrate

Usually neutral to acidic: pH ≤ 7

Colorless octahedrons, "envelopes"

Can be seen in healthy animals or in animals with calcium oxalate uroliths

But can be seen with hypercalciuria or hyperoxaluria (ex. ethylene glycol or oxalate rich plant ingestion)

Develop over time with storage of urine

Magnesium ammonium phosphate (struvite)

Usually neutral to alkaline: pH ≥ 7

Can be seen in healthy dogs, cats and ruminants.

Also common in bacterial-induced alkalinuria and with sterile struvite or mixed uroliths

Uncommon crystals

Illustrated below is a table of crystals that are seen quite infrequently in urine, along with the pH of the urine in which these crystals usually precipitate and some additional information about the crystals. Note, that this is not an exhaustive list and the pictures are not necessarily to scale. For more detailed information and other images of some of these crystals, please refer to the urine crystal page in our routine urinalysis section.

Crystal pH Information

Uric acid

Acidic: pH < 7

Yellow, red-brown or brown, rarely colorless hexagonal plates or needles (rare)

Variable: Rhomboid to diamond crystals, often with pointed ends, hexagonal flat crystals, rosettes, barrel shapes

Calcium oxalate monohydrate

Usually neutral or acidic: pH ≤ 7

Oval, spindle, dumb-bell and picket shaped forms

Oval, spindle or dumb-bell forms are infrequently seen in urine from healthy dogs and cats but can be seen in hypercalciuric conditions and ethylene glycol toxicity

Picket fence form (arrow) are commonly observed in ethylene glycol toxicity in dogs and cats, but can also be seen in animals with hypercalciuria due to other causes (e.g. lymphoma)

Calcium phosphate

Usually neutral or alkaline: pH ≥ 7

Colorless

Blunt-ended needles or prisms, often in rosettes, can be amorphous

Cystine Usually neutral to acidic: pH ≤ 7

Flat colorless hexagonal plates, which often aggregate

Indicative of cystinuria, a rare inborn error of amino acid metabolism affecting many breeds of dogs.

Drug-associated

Variable but usually acidic: pH < 7

Various forms (needles, radiating bundles, round with striations), yellow to colorless

Can be seen in animals on certain drugs: e.g. sulfonamides (mimic various forms of urates), ampicillin (slender needles to sheaves), contrast media, primidone

The image on the left is a sulfonamide crystal (often forms fan-shaped structures) from a dog that was treated with trimethoprim-sulfonamide and sulfasalazine for a chronic urinary tract infection

Tyrosine

Acidic: pH < 7

Fine colorless to brownish needles

Indicate severe liver disease or conditions causing aminoaciduria in humans, but very rare in animals

Unknown crystalsNeedles 

Needle-like bundles

Variable pH All the crystals shown on the left were seen in the urine from dogs. Their identity is uncertain

Variable shape

Not clearly identified as any of the known crystals

Solubility assessed with hydrochloric acid, acetic acid and sodium hydroxide - solubility characteristics do not match those of known crystals

Flat plates resembling cholesterol

Significance dependent on clinical signs and history

 

Infectious agents

Infectious agents of various classes can be observed in urine sediments. In most cases, their significance can be properly assessed only in light of the clinical signs, method of collection, post-collection interval, and other findings in the urinalysis. For instance, urine collected off the floor or some other receptacle could be contaminated by fecal material. Organisms seen in feces (bacteria,Trichuris eggs) may be then misidentified as urinary pathogens. Rarely, organisms that are abundant in peripheral blood may be seen in urine samples with severe blood contamination or hematuria. For example, there have been reports of microfilaria of Dirofilaria immitis being observed in urine of a dog with hematuria and severe microfilaremia due to heartworm infection.

Agent Information

Bacteria: Bacilli

Bacteria can be identified in unstained urine sediments when present in sufficient numbers by their characteristic rod shapes. This is more readily done for bacilli than cocci, which can mimic other structures.

Bacteria are not seen in normal urine (which is sterile). Their presence could indicate an infection (particularly if in large numbers, of a uniform type or accompanied by pyuria) or contamination (more likely in voided samples)

In the image on the left, bacteral rods (some in aggregates) are observed (arrows) in the background along with WBC (arrowhead) in urine from a cat with bacterial cystitis.

 

Bacteria: Cocci Bacterial cocci are readily identified when they form long chains (likely Streptococcus species) as shown in the image of urine at left. However, doublets and clusters must be distinguished from small amorphous crystals, cellular debris, and small fat droplets, all of which show brownian motion in urine.

The image in the lower panel at left shows aggregates of amorphous crystals (arrow).

A Gram-stained smear of urine sediment

Amorphous crystalscould be done to confirm the presence of cocci and distinguish them from non-bacterial structures.

Fungi: Candida Yeasts in unstained urine sediments are round to oval in shape, colorless, and may have obvious budding (upper panel). They often represent contaminants, and are especially suspect if the sample is voided and/or old.

In other circumstances, however, their significance should not be discounted. The pictures shown here, for example, are of fresh urine collected by cystocentesis from a dog that had been on long-term antibiotic and immunosuppressive therapy. The lower photo shows pseudohyphae formation by the yeasts, which were identified on culture as Candida albicans.

Fungi: Hyphae Fungal hyphae in urine sediment preps most commonly represent overgrowth of contaminants in samples where analysis was delayed. 

If seen in a fresh sample, especially one collected by cystocentesis, fungal infection of the kidneys and/or bladder should be suspected. 

Aspergillus terreus (shown at left) has been documented to cause systemic infection including colonization of the renal pelvis.

Parasites Capillaria plica and C. felis-cat are helminth parasite of the canine and feline urinary bladders, respectively. The ova are oval in shape and have bipolar plugs (see picture).

Capillaria eggs must be differentiated fromTrichuris (whipworm) eggs, the latter of which may be seen with fecal contamination of the urine. If the ova were seen in a well- handled urine collected by cystocentesis, fecal contamination could be ruled out. Additionally, the ova ofCapillaria (shown in left upper panel) are rougher in texture compared to the smooth, yellowish eggs of Trichuris (shown in left lower panel), Capillaria ova often have one straighter side and the bipolar plugs on Trichuris resemble screws of a light bulb (arrow).

Dioctophyma renale, the giant kidney worm, has large, yellow-brown, thick-walled ova with a characteristic wavy surface (not pictured). Eggs may be seen in urine if a

gravid female worm is present. Though endemic in areas of Canada, the infection is very rare in the United States.

Casts

The image below represents different casts seen in urine at the same magnification and lighting. Shown are hyaline, hyaline casts with adherent fat, granular and waxy casts.

Hyaline casts: These can be quite difficult to see in wet preparations of urine sediments with light microscopy, even with the condenser of the microscope racked down. They are much easier to visualize using phase contrast, however phase is usually not available on most microscopes. They become more visible with regular light microscopy if fat sticks to the protein matrix (Tamm-Horsfall mucoprotein) that makes up the hyaline cast (hyaline with fat) or particulate material from degenerating cells is present within the cast matrix (hyaline to finely granular cast).

Cellular casts: These have distinct cells within the protein matrix - if the cells are of epithelial origin (i.e., not WBCs or RBCs), they are called epithelial casts..

Granular casts: As cells within the protein cast matrix break down, the cast becomes coarsely then finely granular.

Waxy casts: Waxy casts are the final stage of cast degeneration (usually originating from cellular and granular casts). Compared to hyaline casts, they are readily observable because they have a smooth appearance, no internal texture, and are more refractile than the surrounding urine.

Of all these casts, hyaline (with or without adherent fat) and finely granular casts may be seen in urine from healthy animals. Cellular, coarsely granular and waxy casts always indicate renal pathology. For more information on the meaning of casts, view the routine urinalysis section.

Contaminants or other constituents

Extraneous contaminating materials of many types can make their way into urine specimens, especially those collected by free catch in the courtyard or the barns. Owners may sometimes collect specimens in containers that are less than clean, let alone sterile.

Striving for optimal collection and transport of specimens will help maximize useful results and minimize confusing findings. Specimens mailed to laboratories without refrigeration or preservatives are subject to microbial overgrowth, whether contaminants or pathogens. Refrigeration is perhaps the best all-around method for preserving a specimen. 

Cells Information

Fecal parasites

Fecal material, including eggs of intestinal parasites, sometimes contaminates voided urine samples.

For example, the images on the left show a urine sediment of a cat stained with Sedi-stain. In the upper panel is a low magnification view showing a packet of eggs. In the lower panel, higher magnification reveals the internal structure of the hexacanth embryos of Dipylidium caninum, a tapeworm.

 

Environmental fungi

Mold spores come in a variety of shapes, sizes and colors

Shown here is a brownish Alternaria spore surrounded by amorphous crystals and a few lipid droplets.Alternaria is a dematiaceous fungus that is ubiquitous in the environment

Fibers

Cotton, plant, and paper fibers may mimic parasite larvae or urinary casts

Microbial overgrowth 

Shown here is a dense mat of fungal hyphae in canine urine which wasseveral days in transit. Since fungal infection of the urinary tract in dogs is quite uncommon, the odds are that this represents overgrowth of contaminants.

Bacteria, whether pathogens or contaminants, can multiply when analysis is delayed. This often clouds interpretation of the sediment examination and culture results.

Mucus Mucus can be observed in some urine samples, particularly that collected from horses (hence it is a constituent and not a contaminant). Mucus is far more infrequent in urine samples from other species

Strands of mucus can mimic hyaline casts, particularly when viewed under regular light microscopy (upper

panel on left)

Compared to casts: Mucus is more irregular in shape and has irregular borders with tapered ends.

Pollen

Pollen grains are generally round to oval and some have a yellow to brown tint.

They are most likely to be confused for parasitic ova. A good knowledge of the actual appearance of the few true parasite eggs that can occur in urine is easier to achieve than specific recognition of all types of pollen and mold spores. Again, optimizing specimen collection and handling will reduce the chances of seeing potentially confusing structures.

Starch crystals (Biosorb)

Lubricant in surgical and examination gloves

Common contaminants in urine sediments and cytology smears.

Variable in size, round to polygonal in shape, colorless, refractile (due to their crystalline nature) and usually have a circular or Y-shaped "dot" in the center (arrow in image on left).