How do you interpret a urine dipstick result?

How to Read and Interpret a Urine Dipstick

Urine dipstick testing is a rapid diagnostic tool that provides valuable information about multiple urinary parameters, with proper interpretation requiring understanding of each parameter's significance and limitations.

General Principles

• Use fresh urine sample (within 1 hour of collection at room temperature or 4 hours if refrigerated) 1
• Ensure proper technique when dipping the strip and timing the reading
• Automated readers are preferred over visual interpretation when available due to standardization 2
• Results should be interpreted in clinical context, not in isolation

Parameters and Interpretation

1. Leukocyte Esterase

• What it detects: Enzyme from white blood cells (WBCs)
• Interpretation:
  • Positive: Suggests pyuria (WBCs in urine)
  • Sensitivity: 83% (67-94%)
  • Specificity: 78% (64-92%) 1
  • More sensitive but less specific for UTI than nitrite test
  • False negatives: Early infection, certain antibiotics, high glucose, vitamin C

2. Nitrite

• What it detects: Conversion of dietary nitrates to nitrites by bacteria
• Interpretation:
  • Positive: Highly specific for bacteriuria (98% specificity)
  • Sensitivity: 53% (15-82%) 1
  • False negatives: Frequent voiding (requires 4+ hours in bladder), non-nitrate reducing organisms
  • A positive nitrite test effectively rules in UTI (99% specificity) 3

3. Combined Leukocyte Esterase and Nitrite

• Interpretation:
  • Either test positive: 93% sensitivity, 72% specificity 1
  • Both tests positive: 96% specificity 1
  • Either test negative: 95% negative predictive value for UTI 4

4. Blood/Hemoglobin

• What it detects: Intact RBCs or free hemoglobin
• Interpretation:
  • Positive: Suggests hematuria, hemoglobinuria, or myoglobinuria
  • Always confirm with microscopy 5
  • Causes: UTI, stones, trauma, malignancy, glomerular disease, exercise

5. Protein

• What it detects: Primarily albumin
• Interpretation:
  • Negative: <30 mg/dL
  • Trace: 30 mg/dL
  • 1+: 100 mg/dL
  • 2+: 300 mg/dL
  • 3+: 1000 mg/dL
  • 4+: >2000 mg/dL
  • If positive (≥1+), confirm with protein/creatinine ratio 1
  • Protein/creatinine ratio ≥30 mg/mmol (0.3 mg/mg) is abnormal 1

6. pH

• Normal range: 4.5-8.0
• Interpretation:
  • Alkaline (>7.5): May suggest urea-splitting organisms (Proteus)
  • Acidic (<5.5): May suggest acidifying diet, certain medications, metabolic acidosis

7. Specific Gravity

• Normal range: 1.005-1.030
• Interpretation:
  • High (>1.030): Dehydration, glycosuria
  • Low (<1.005): Diabetes insipidus, overhydration, renal tubular dysfunction

8. Glucose

• Normal: Negative
• Interpretation:
  • Positive: Suggests hyperglycemia (diabetes), renal tubular dysfunction
  • Appears when blood glucose exceeds renal threshold (~180 mg/dL)

9. Ketones

• Normal: Negative
• Interpretation:
  • Positive: Suggests ketosis (diabetic ketoacidosis, starvation, high-fat diets)

10. Bilirubin/Urobilinogen

• Normal: Negative/Normal
• Interpretation:
  • Positive bilirubin: Suggests liver disease or biliary obstruction
  • Elevated urobilinogen: Suggests hemolysis or liver disease

Clinical Application Algorithm

1. For suspected UTI:

   • If nitrite positive → High probability of UTI (consider treatment) 3
   • If nitrite negative but leukocyte esterase positive → Moderate probability (consider microscopy)
   • If both negative → Low probability of UTI (consider alternative diagnosis) 3

2. For proteinuria evaluation:

   • If dipstick positive (≥1+) → Perform protein/creatinine ratio 1
   • If protein/creatinine ratio ≥30 mg/mmol (0.3 mg/mg) → Abnormal proteinuria
   • Consider causes: UTI, exercise, fever, orthostatic proteinuria, kidney disease

3. For hematuria evaluation:

   • Always confirm with microscopy 5
   • Differentiate between:
     • RBCs (true hematuria)
     • Hemoglobinuria (intravascular hemolysis)
     • Myoglobinuria (muscle breakdown)

Common Pitfalls and Limitations

• False positives:

  • Leukocyte esterase: Contamination, certain medications
  • Nitrite: Contaminated specimen, prolonged storage
  • Protein: Highly concentrated urine, alkaline pH, gross hematuria
  • Blood: Menstrual contamination, vigorous exercise, contamination

• False negatives:

  • Leukocyte esterase: Vitamin C, high glucose, certain antibiotics
  • Nitrite: Frequent voiding, non-nitrate reducing organisms
  • Protein: Dilute urine, non-albumin proteins

• Technical considerations:

  • Ensure proper timing when reading results
  • Avoid contamination of dipstick
  • Store dipsticks properly (moisture affects results)
  • Calibrate automated readers regularly 2

Remember that dipstick testing is a screening tool and may require confirmation with microscopy and/or culture for definitive diagnosis, particularly for suspected UTI or when evaluating proteinuria or hematuria.