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Quick Reference
  • WBCs (Leukocytes): 0-5 cells/hpf (normal)
  • RBCs (Erythrocytes): 0-2 cells/hpf (normal)
  • Epithelial Cells: Few squamous cells (normal)
  • Casts: Rare hyaline casts (may be normal)
  • Crystals: Varies by urine pH (may be normal)
  • Bacteria: None to rare (normal)
  • Primary Use: Diagnosis of UTI, kidney disease, glomerulonephritis, and urinary tract disorders
  • Sample Type: Fresh urine specimen, examined within 1-2 hours of collection
  • Key Point: RBC casts are pathognomonic for glomerulonephritis; dysmorphic RBCs suggest glomerular bleeding

Test Description

Urine microscopy is the microscopic examination of centrifuged urine sediment to identify and quantify cellular elements, casts, crystals, bacteria, and other formed elements. This is an essential component of a complete urinalysis and provides critical diagnostic information that cannot be obtained from dipstick testing alone.

Microscopic examination helps differentiate the causes of hematuria, identify the site of infection or inflammation within the urinary tract, diagnose glomerular disease, and detect kidney stones. The presence of specific elements like RBC casts, WBC casts, or crystals can provide definitive clues to the underlying pathology.

Elements Examined

  • White Blood Cells (WBCs): Indicate inflammation or infection in the urinary tract
  • Red Blood Cells (RBCs): Indicate bleeding from any level of the urinary tract or kidney
  • Epithelial Cells: Squamous (contamination), transitional (bladder/urethra), or renal tubular (kidney damage)
  • Casts: Cylindrical structures formed in renal tubules that indicate renal origin of pathology
  • Crystals: Crystallized substances that may indicate metabolic disorders or kidney stones
  • Bacteria and Yeast: Microorganisms indicating infection or contamination
Normal Ranges

Normal urine sediment may contain small numbers of cells and occasional hyaline casts. Findings are reported per high-power field (hpf) for cells and per low-power field (lpf) for casts.

Swipe to see more
Element Normal Range Clinical Significance
WBCs 0-5 cells/hpf >5/hpf abnormal (pyuria)
RBCs 0-2 cells/hpf >3/hpf abnormal (hematuria)
Squamous Epithelial Cells Few Many = contamination
Transitional Epithelial Cells Rare Bladder/urethra origin
Renal Tubular Cells None Indicates tubular damage
Hyaline Casts 0-2/lpf (rare) May be normal or benign
Other Casts None Always pathologic
Bacteria None to rare Many = UTI or contamination
Crystals Variable Depends on pH and type
Important Considerations:
  • Urine must be examined within 1-2 hours of collection; old specimens may have cell lysis or bacterial overgrowth
  • First morning void provides the most concentrated specimen and optimal detection of abnormalities
  • Centrifugation technique and high-power field size may vary between laboratories
  • Findings must be correlated with dipstick results and clinical context
Clinical Significance

White Blood Cells (Pyuria)

WBCs in urine indicate inflammation or infection in the urinary tract. The degree of pyuria and associated findings help localize the source.

Significance of WBC Counts:

  • >5 WBCs/hpf: Abnormal; suggests UTI or inflammation
  • >10 WBCs/hpf: Significant pyuria; highly suggestive of UTI when symptomatic
  • >50 WBCs/hpf: Severe pyuria; acute bacterial cystitis or pyelonephritis

Causes of Pyuria:

  • Urinary Tract Infection (UTI): Most common cause; typically accompanied by bacteriuria
  • Pyelonephritis: Upper UTI with WBC casts indicating renal origin
  • Interstitial Nephritis: Drug-induced (NSAIDs, antibiotics) with eosinophiluria and WBC casts
  • Sexually Transmitted Infections (STIs): Urethritis from Chlamydia, Gonorrhea
  • Sterile Pyuria: Pyuria without bacteriuria; consider tuberculosis, interstitial nephritis, or recent antibiotic use

Red Blood Cells (Hematuria)

Hematuria can originate from anywhere in the urinary tract. The morphology of RBCs and associated findings help differentiate glomerular from non-glomerular sources.

Significance of RBC Counts:

  • >3 RBCs/hpf: Abnormal; requires evaluation
  • Dysmorphic RBCs: Irregular, distorted RBCs indicating glomerular disease (passed through damaged glomeruli)
  • Isomorphic RBCs: Normal-appearing RBCs suggesting lower urinary tract bleeding

RBC Casts = Glomerulonephritis:

  • RBC Casts: Diagnostic for glomerulonephritis; indicate bleeding of renal glomerular origin
  • Causes: Post-streptococcal GN, IgA nephropathy, lupus nephritis, vasculitis, rapidly progressive GN

Other Causes of Hematuria:

  • Kidney Stones (Nephrolithiasis): Often accompanied by crystals and severe flank pain
  • Urinary Tract Infection: Hemorrhagic cystitis with pyuria and bacteriuria
  • Trauma: Blunt or penetrating kidney injury, Foley catheter trauma
  • Malignancy: Bladder cancer, renal cell carcinoma (painless hematuria in elderly)
  • Benign Prostatic Hyperplasia (BPH): In older men
  • Exercise-Induced: "Runner's hematuria" resolves with rest

Casts (Indicate Renal Origin)

Casts are cylindrical structures formed in the renal tubules and always indicate that the pathology originates from the kidney itself, not the lower urinary tract. Different types of casts indicate specific renal conditions.

Hyaline Casts:

  • Appearance: Clear, transparent casts composed of Tamm-Horsfall protein
  • Significance: May be normal (0-2/lpf), especially after dehydration or vigorous exercise
  • Increased in: Dehydration, concentrated urine, fever, exercise, diuretic use

RBC Casts:

  • Appearance: Reddish-brown casts containing embedded red blood cells
  • Significance: Pathognomonic (diagnostic) for glomerulonephritis
  • Causes: Post-streptococcal GN, IgA nephropathy, lupus nephritis, vasculitis, rapidly progressive GN

WBC Casts:

  • Appearance: Casts containing embedded white blood cells
  • Significance: Indicate renal parenchymal infection or inflammation
  • Causes: Pyelonephritis (most common), acute interstitial nephritis, lupus nephritis

Granular Casts:

  • Appearance: Coarse or fine granular texture from degraded cells
  • Significance: Non-specific indicator of renal tubular injury
  • Causes: Acute tubular necrosis (ATN), chronic kidney disease (CKD), glomerulonephritis

Waxy Casts:

  • Appearance: Broad, waxy, homogeneous appearance with blunt ends
  • Significance: Indicate chronic, severe kidney disease
  • Causes: Advanced chronic kidney disease, end-stage renal disease (ESRD)

Broad Casts:

  • Appearance: Wide casts formed in dilated, damaged tubules
  • Significance: "Renal failure casts" indicating severe chronic kidney disease or acute kidney injury
  • Association: End-stage renal disease, severe oliguria

Fatty Casts:

  • Appearance: Contain lipid droplets or oval fat bodies; appear refractile under polarized light ("Maltese cross")
  • Significance: Indicate nephrotic syndrome with massive proteinuria
  • Causes: Minimal change disease, focal segmental glomerulosclerosis (FSGS), membranous nephropathy, diabetic nephropathy

Crystals

Crystals in urine may be normal or pathologic depending on the type, urine pH, and clinical context. Some crystals are associated with kidney stone formation or specific toxicities.

Uric Acid Crystals:

  • Appearance: Yellow-brown, diamond or rhomboid shaped
  • pH: Acidic urine (pH <5.5)
  • Causes: Gout, tumor lysis syndrome, high purine diet, uric acid kidney stones

Calcium Oxalate Crystals:

  • Appearance: Envelope-shaped (monohydrate) or dumbbell-shaped (dihydrate)
  • pH: Acidic to neutral urine
  • Significance: May be normal, but can indicate hyperoxaluria or ethylene glycol poisoning (antifreeze ingestion)
  • Causes: Calcium oxalate kidney stones, ethylene glycol toxicity (with metabolic acidosis)

Triple Phosphate (Struvite) Crystals:

  • Appearance: "Coffin lid" shaped
  • pH: Alkaline urine (pH >7.0)
  • Causes: UTI with urease-producing bacteria (Proteus, Klebsiella, Pseudomonas), staghorn calculi

Cystine Crystals:

  • Appearance: Hexagonal, flat plates (benzene ring shape)
  • pH: Acidic urine
  • Causes: Cystinuria (genetic disorder causing cystine kidney stones)

Epithelial Cells

Different types of epithelial cells indicate the source of cellular shedding within the urinary tract.

Squamous Epithelial Cells:

  • Source: Distal urethra, vagina, or external genitalia
  • Significance: Usually indicate contamination from poor collection technique; large numbers invalidate urinalysis

Transitional Epithelial Cells:

  • Source: Bladder, ureters, renal pelvis
  • Significance: May indicate lower urinary tract irritation, inflammation, or (rarely) transitional cell carcinoma

Renal Tubular Epithelial Cells:

  • Source: Renal tubules
  • Significance: Indicate tubular damage
  • Causes: Acute tubular necrosis (ATN), acute interstitial nephritis, transplant rejection, toxic injury
Interfering Factors

Pre-Analytical Factors

  • Delayed Examination: Urine older than 2 hours causes cell lysis, bacterial overgrowth, and cast dissolution
  • Improper Storage: Room temperature causes cellular degradation; refrigeration can cause crystal precipitation
  • Contamination: Vaginal secretions, menstrual blood, or skin flora from poor collection technique
  • Dilute Urine: Low specific gravity may reduce cast and cell counts
  • Hypotonic Urine: Can cause RBC lysis leading to falsely low RBC count

Factors Causing False Positive Results

Increased WBCs (Non-Infectious)

  • Vaginal Contamination: Vaginal leukocytes, especially during vaginitis or menstruation
  • Recent Sexual Activity: Semen contains WBCs
  • Medications: Drug-induced interstitial nephritis (NSAIDs, antibiotics, PPIs)

Increased RBCs (Non-Pathologic)

  • Menstrual Contamination: Collect midstream "clean catch" to avoid menstrual blood
  • Vigorous Exercise: "Runner's hematuria" resolves with rest
  • Foley Catheter Trauma: Traumatic catheterization

Factors Causing False Negative Results

  • Alkaline Urine: RBC lysis in alkaline pH may cause false negative microscopy but positive dipstick for blood
  • Dilute Urine: Low cell and cast concentrations may be missed
  • Delayed Processing: Cell lysis reduces cell counts

Medications Affecting Results

  • Cause Pyuria: NSAIDs, penicillins, cephalosporins, sulfonamides, rifampin, PPIs (interstitial nephritis)
  • Cause Hematuria: Anticoagulants (warfarin, DOACs), cyclophosphamide (hemorrhagic cystitis)
  • Cause Crystalluria: Acyclovir, indinavir, sulfadiazine, methotrexate
Clinical Pearls
Clinical Pearl
"RBC casts = glomerulonephritis": RBC casts are pathognomonic (diagnostic) for glomerulonephritis. They indicate bleeding from damaged glomeruli and are never normal. Immediate nephrology referral is warranted.
Clinical Pearl
WBC Casts Indicate Pyelonephritis: WBC casts differentiate upper UTI (pyelonephritis) from lower UTI (cystitis). Presence of WBC casts confirms renal parenchymal infection requiring more aggressive antibiotic therapy.
Clinical Pearl
Hyaline Casts Can Be Normal: Small numbers of hyaline casts (0-2/lpf) may be seen in normal urine, especially after exercise, dehydration, or in concentrated urine. They are not always pathologic.
Clinical Pearl
Broad Casts = End-Stage Renal Disease: Broad, waxy casts ("renal failure casts") indicate severely dilated and damaged tubules. They are associated with advanced chronic kidney disease or acute kidney injury with poor prognosis.
Calcium Oxalate Crystals in Ethylene Glycol Poisoning: Presence of calcium oxalate crystals with metabolic acidosis, elevated osmolar gap, and acute kidney injury suggests ethylene glycol (antifreeze) poisoning. This is a medical emergency requiring fomepizole or hemodialysis.
Clinical Pearl
Dysmorphic RBCs Suggest Glomerular Disease: Dysmorphic (distorted, irregular) RBCs with acanthocytes ("Mickey Mouse ears") indicate glomerular bleeding. Isomorphic (normal-appearing) RBCs suggest lower urinary tract bleeding.
Sterile Pyuria (WBCs Without Bacteria): Consider tuberculosis (TB), interstitial nephritis, recent antibiotic use, or sexually transmitted infections (Chlamydia, Gonorrhea). Send urine culture for TB and STI testing as appropriate.
Clinical Pearl
Triple Phosphate Crystals + UTI = Urease-Producing Bacteria: Struvite (triple phosphate) crystals in alkaline urine with UTI indicate urease-producing organisms (Proteus, Klebsiella). These bacteria can form staghorn calculi requiring surgical intervention.
Clinical Pearl
Fatty Casts and Oval Fat Bodies = Nephrotic Syndrome: Lipid-containing casts with "Maltese cross" appearance under polarized light indicate massive proteinuria and nephrotic syndrome. Expect hypoalbuminemia and edema.
Many Squamous Epithelial Cells = Contaminated Specimen: Large numbers of squamous cells indicate poor collection technique with contamination from skin or genital secretions. The specimen should be recollected using proper "clean catch" midstream technique.
Renal Tubular Epithelial Cells = Acute Tubular Necrosis: Presence of renal tubular cells suggests tubular injury. Common in ATN from ischemia, nephrotoxic drugs (aminoglycosides, contrast), or pigment nephropathy (rhabdomyolysis).
Clinical Pearl
Examine Urine Fresh: Urine microscopy should be performed within 1-2 hours of collection. Delayed examination causes cell lysis, bacterial overgrowth, and cast dissolution leading to false negative results.
References
  1. Kratz, A., Ferraro, M., Sluss, P. M., & Lewandrowski, K. B. (2004). Laboratory reference values. New England Journal of Medicine, 351, 1548-1564.
  2. Lee, M. (Ed.). (2009). Basic skills in interpreting laboratory data. Ashp.
  3. Farinde, A. (2021). Lab values, normal adult: Laboratory reference ranges in healthy adults. Medscape. https://emedicine.medscape.com/article/2172316-overview?form=fpf
  4. Nickson, C. (n.d.). Critical Care Compendium. Life in the Fast Lane • LITFL. https://litfl.com/ccc-critical-care-compendium/
  5. Farkas, Josh MD. (2015). Table of Contents - EMCrit Project. EMCrit Project. https://emcrit.org/ibcc/toc/
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