CELL (URINE)

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 >100Normal: 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

Source : © Cornell University