How do I interpret a urinalysis?

How to Interpret a Urinalysis

A comprehensive urinalysis interpretation requires systematic evaluation of physical characteristics, chemical parameters, and microscopic examination to accurately diagnose urinary tract and systemic conditions. This approach ensures proper identification of abnormalities that may indicate significant underlying pathology.

Components of Urinalysis

Physical Characteristics

• Color: Normal urine ranges from pale yellow to amber; abnormal colors may indicate pathology (e.g., red/brown suggests hematuria, dark yellow indicates concentrated urine) 1
• Clarity: Cloudy urine often results from precipitated phosphate crystals in alkaline urine or pyuria 2
• Odor: Strong odor may indicate concentrated specimen rather than infection 2
• Volume: Helps assess hydration status and kidney function 3
• Specific gravity: Provides reliable assessment of hydration status (normal range 1.005-1.030) 2

Chemical Parameters (Dipstick)

• pH: Normal range 4.5-8.0; alkaline pH suggests UTI with urease-producing organisms 3
• Protein: Persistent proteinuria requires further workup; transient proteinuria may be benign 2
• Blood: Positive result requires microscopic confirmation; false positives can occur with hemoglobinuria, myoglobinuria, or certain medications 4
• Nitrite: High specificity (98%) but lower sensitivity (53%) for UTI; formed by bacterial metabolism of urinary nitrates 5
• Leukocyte esterase: Higher sensitivity (83%) but lower specificity (78%) for UTI 4
• Glucose: Suggests diabetes mellitus or renal tubular dysfunction 3
• Ketones: Indicates fat metabolism, seen in diabetic ketoacidosis, starvation, or high-fat diets 3
• Bilirubin/Urobilinogen: Abnormal values suggest liver disease or hemolysis 3

Microscopic Examination

• Red blood cells: ≥3 RBCs/HPF defines microscopic hematuria; requires evaluation 4
• White blood cells: >5 WBCs/HPF suggests inflammation or infection 3
• Epithelial cells: Squamous cells indicate contamination; renal tubular cells suggest kidney damage 3
• Casts: Hyaline casts may be normal; cellular casts indicate specific renal pathologies 3
• Crystals: May be normal or indicate metabolic disorders or medication effects 1
• Bacteria: Presence suggests infection; >105 CFU/mL is significant in properly collected specimens 4

Interpretation Algorithm

Step 1: Evaluate Collection Method

• Clean-catch midstream: Standard method for most patients 2
• Catheterization: More reliable, especially in pediatric patients 4
• Suprapubic aspiration: Gold standard for infants or when contamination is likely 4

Step 2: Assess Physical Characteristics

• Document color, clarity, and odor 1
• Measure specific gravity to assess concentration 2

Step 3: Interpret Dipstick Results

• Positive blood: Requires microscopic confirmation; don't rely solely on dipstick 4
• Positive nitrite + leukocyte esterase: 93% sensitivity for UTI 4
• Positive protein: Quantify with protein-to-creatinine ratio if persistent 2

Step 4: Examine Microscopic Findings

• Hematuria: ≥3 RBCs/HPF is abnormal; evaluate for glomerular vs. non-glomerular source 4
• Pyuria: >5 WBCs/HPF suggests inflammation or infection 3
• Bacteriuria: Presence of bacteria with pyuria strongly suggests UTI 4

Clinical Applications

Urinary Tract Infection

• Diagnostic criteria: Positive leukocyte esterase and/or nitrite, plus pyuria and/or bacteriuria 5
• Management: Uncomplicated UTIs with positive leukocyte esterase and nitrite can be treated without culture 2
• Special populations: In frail or comorbid older patients, UTI diagnosis requires both urinalysis abnormalities AND specific symptoms (dysuria, frequency, urgency, or costovertebral angle tenderness) 5

Hematuria

• Microscopic hematuria: ≥3 RBCs/HPF requires evaluation for urologic malignancy 4
• Gross hematuria: Requires urgent evaluation due to stronger association with cancer 5
• Risk assessment: Consider patient factors including age, sex, smoking history 4

Proteinuria

• Transient proteinuria: Often benign, may occur with fever, exercise 2
• Persistent proteinuria: Requires nephrology evaluation 2

Common Pitfalls to Avoid

• Relying solely on dipstick: Always confirm hematuria with microscopic examination 4
• Ignoring collection method: Bag specimens in children have high contamination rates 4
• Attributing hematuria to anticoagulants: Anticoagulation therapy is not a cause of hematuria and requires full evaluation 4
• Neglecting to repeat testing: After treating presumed benign causes, repeat urinalysis to confirm resolution 4
• Under-evaluating women: Women with hematuria require thorough evaluation, as they often receive incomplete diagnostic workups despite higher case-fatality rates for bladder cancer 4
• Misinterpreting timing: Urine is unstable; changes begin immediately after collection, so prompt examination (within 2 hours) is essential 2

Special Considerations

Pediatric Patients

• Collection method impacts interpretation; catheterization or suprapubic aspiration preferred 4
• UTI diagnosis requires both urinalysis abnormalities and positive culture (≥50,000 CFU/mL) 5

Elderly Patients

• Higher risk of urologic malignancy with microhematuria 4
• UTI diagnosis requires specific symptoms; avoid treating asymptomatic bacteriuria 5
• Antimicrobial treatment generally aligns with other age groups unless complicating factors present 5