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Cells

Leukocytes may be seen under low- and high-power magnification (Figure 1). Men normally have fewer than two white blood cells (WBCs) per HPF; women normally have fewer than five WBCs per HPF.

Epithelial cells often are present in the urinary sediment. Squamous epithelial cells are large and irregularly shaped, with a small nucleus and fine granular cytoplasm; their presence suggests contamination. The presence of transitional epithelial cells is normal. These cells are smaller and rounder than squamous cells, and they have larger nuclei. The presence of renal tubule cells indicates significant renal pathology (Figure 2). Erythrocytes are best visualized under high-power magnification. Dysmorphic erythrocytes, which have odd shapes because of their passage through an abnormal glomerulus, suggest glomerular disease.

TABLE 6 Urinary Casts and Associated Pathologic Conditions
Type of cast	Composition	Associated conditions
Hyaline	Mucoproteins	Pyelonephritis, chronic renal disease May be a normal finding
Erythrocyte	Red blood cells	Glomerulonephritis May be a normal finding in patients who play contact sports
Leukocyte	White blood cells	Pyelonephritis, glomerulonephritis, interstitial nephritis, renal inflammatory processes
Epithelial	Renal tubule cells	Acute tubular necrosis, interstitial nephritis, eclampsia, nephritic syndrome, allograft rejection, heavy metal ingestion, renal disease
Granular	Various cell types	Advanced renal disease
Waxy	Various cell types	Advanced renal disease
Fatty	Lipid-laden renal tubule cells	Nephrotic syndrome, renal disease, hypothyroidism
Broad	Various cell types	End-stage renal disease
Information from reference 38.

Casts

Casts in the urinary sediment may be used to localize disease to a specific location in the genitourinary tract (Table 6).38 Casts, which are a coagulum of Tamm- Horsfall mucoprotein and the trapped contents of tubule lumen, originate from the distal convoluted tubule or collecting duct during periods of urinary concentration or stasis, or when urinary pH is very low. Their cylindrical shape reflects the tubule in which they were formed and is retained when the casts are washed away. The predominant cellular elements determine the type of cast: hyaline, erythrocyte, leukocyte, epithelial, granular, waxy, fatty, or broad (Figure 3).

Figure 4. Urinary crystals. (A) Calcium oxalate crystals (arrows; 100 X); (B) uric acid crystals (100 X); (C) triple phosphate crystals with amorphous phosphates (400 X); (D) cystine crystals (100 X).

Crystals

Crystals may be seen in the urinary sediment of healthy patients (Figure 4). Calcium oxalate crystals have a refractile square "envelope" shape that can vary in size. Uric acid crystals are yellow to orange-brown and may be diamond- or barrel-shaped. Triple phosphate crystals may be normal but often are associated with alkaline urine and UTI (typically associated with Proteus species). These crystals are colorless and have a characteristic "coffin lid" appearance. Cystine crystals are colorless, have a hexagonal shape, and are present in acidic urine, which is diagnostic of cystinuria.

Bacteriuria

Gram-negative streptococci and staphylococci can be distinguished by their characteristic appearance under high-powered magnification.

Gram staining can help guide antibiotic therapy, but it is not indicated in routine outpatient practice. Clean-catch specimens from female patients frequently are contaminated by vaginal flora. In these patients, five bacteria per HPF represents roughly 100,000 colony-forming units (CFU) per mL, the classic diagnostic criterion for asymptomatic bacteriuria and certainly compatible with a UTI. In symptomatic patients, a colony count as low as 100 CFU per mL suggests UTI, and antibiotics should be considered. The presence of bacteria in a properly collected male urine specimen is suggestive of infection, and a culture should be obtained.

The authors indicate that they do not have any conflicts of interest. Sources of funding: none reported.

Figures 1 through 4 reprinted from the National Institutes of Health Clinical Center Department of Laboratory Medicine, Bethesda, Md.

The Authors

JEFF A. SIMERVILLE, M.D., is a fifth-year resident in urology at Georgetown University Medical Center, Washington, D.C. He received his medical degree from Georgetown University School of Medicine.

WILLIAM C. MAXTED, M.D., is professor of urology at Georgetown University School of Medicine, where he received his medical degree and completed a residency in urology.

JOHN J. PAHIRA, M.D., is professor of urology at Georgetown University School of Medicine. He received his medical degree from Pennsylvania State University Milton S. Hershey Medical Center College of Medicine, Hershey, and a residency in urology at the Hospital of the University of Pennsylvania, Philadelphia.

Address correspondence to Jeff A. Simerville, M.D., 6641 Wakefield Dr., #411, Alexandria, VA 22307 (e-mail: jsimerville@cox.net). Reprints are not available from the authors.

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