How do you interpret urinalysis results?

Urinalysis Interpretation

Proper urinalysis interpretation requires assessment of physical characteristics, biochemical parameters, and microscopic sediment evaluation, with interpretation based on the collection method and clinical context to maximize diagnostic accuracy. 1, 2

Components of Urinalysis Interpretation

Physical Characteristics

• Color: Normal urine ranges from pale yellow to amber; abnormal colors may indicate:

  • Red/pink: Hematuria, hemoglobinuria, myoglobinuria
  • Dark brown/tea-colored: Bilirubin, severe dehydration
  • Cloudy: Possible infection, crystals, or cellular debris

• Clarity: Should be clear; cloudiness suggests infection, crystals, cells, or protein

• Volume: Varies based on hydration status and renal function

Biochemical Parameters (Dipstick)

Test	Interpretation	Sensitivity/Specificity
Leukocyte esterase	Indicates pyuria (WBCs in urine)	Sensitivity: 83% (67-94%) Specificity: 78% (64-92%) [1]
Nitrite	Positive when bacteria convert nitrates to nitrites	Sensitivity: 53% (15-82%) Specificity: 98% (90-100%) [1]
Combined (either positive)	Higher sensitivity for UTI	Sensitivity: 93% (90-100%) Specificity: 72% (58-91%) [1]
Blood	Indicates hematuria or hemoglobinuria	Requires microscopic confirmation
Protein	Abnormal when >30 mg/dL	Evaluate with clinical context [3]
Glucose	Abnormal when present	Consider diabetes, pregnancy, or renal tubular dysfunction
Ketones	Abnormal when present	Consider diabetic ketoacidosis, starvation
pH	Normal range: 4.5-8.0	Acidic: metabolic acidosis, ketosis Alkaline: UTI with urea-splitting organisms
Specific gravity	Normal range: 1.005-1.030	Evaluates concentrating ability
Bilirubin/Urobilinogen	Abnormal when present	Indicates liver disease or hemolysis

Microscopic Examination

• Red Blood Cells (RBCs):

  • Normal: 0-3 RBCs per high power field (HPF)

  • 3 RBCs/HPF indicates hematuria 4

  • Requires evaluation, especially in adults over 35 years

• White Blood Cells (WBCs):

  • Normal: 0-5 WBCs/HPF
  • Pyuria defined as ≥10 WBCs/mm³ on enhanced urinalysis or ≥5 WBCs/HPF on centrifuged specimen 1
  • Pyuria + symptoms strongly suggests UTI

• Bacteria:

  • Presence of any bacteria on Gram stain of uncentrifuged urine has 93% sensitivity and 4% false-positive rate 4
  • Centrifugation before Gram staining can decrease specificity 4

• Epithelial Cells:

  • Squamous cells suggest contamination
  • Renal tubular cells may indicate renal tubular damage

• Casts:

  • Hyaline casts: May be normal
  • RBC casts: Glomerular disease
  • WBC casts: Pyelonephritis
  • Granular/waxy casts: Acute tubular necrosis or chronic kidney disease

• Crystals:

  • Identification helps diagnose stone disease
  • Some crystals normal in concentrated urine

Clinical Correlation and Interpretation

UTI Diagnosis

• Diagnostic criteria: Symptoms + pyuria + bacteriuria 1
• Recommended threshold: ≥50,000 CFU/mL + pyuria + symptoms 1
• In symptomatic patients, even growth as low as 10² CFU/mL could reflect infection 5
• Positive leukocyte esterase with symptoms indicates treatment for UTI 1

Specimen Collection and Handling

• Process urine within 2 hours or refrigerate to prevent false results 1
• Proper collection technique is critical to prevent false positive results 1
• Collection method affects interpretation:
  • Clean-catch: >10⁵ CFU/mL of single organism suggests UTI
  • Catheterized: 10³-10⁵ CFU/mL threshold
  • Suprapubic aspiration: >10² CFU/mL or any growth 4

Special Considerations

• Asymptomatic bacteriuria:

  • Common, especially in older women
  • Should not be treated except in pregnancy or before urologic procedures 1

• Hematuria evaluation:

  • Always combine dipstick with microscopic examination 3
  • Gross hematuria has stronger association with cancer and serious conditions 4
  • Consider referral for urologic evaluation, especially with risk factors 4

• Pyuria without bacteriuria:

  • Consider sexually transmitted infections, kidney stones, interstitial cystitis
  • Common in older adults with lower urinary tract symptoms 5

Common Pitfalls to Avoid

1. False negative dipstick results: In patients with high probability of UTI based on symptoms, negative dipstick does not rule out UTI 5

2. Over-reliance on colony count: Interpret in context of symptoms and pyuria 1

3. Treating contaminated specimens: Multiple organisms usually indicate contamination 4

4. Delayed processing: Can lead to bacterial overgrowth and false positives 1

5. Missing intermittent hematuria: Consider repeated testing (up to 3 times) 4

6. Treating asymptomatic bacteriuria: Avoid except in pregnancy or before urologic procedures 1

7. Ignoring sex disparities: Women have lower rates of referral despite higher case-fatality rates for bladder cancer 4

8. PCR inhibition: Can lead to false negative results in molecular testing; proper specimen handling is critical 1