How do you interpret a urinalysis?

How to Read and Interpret a Urinalysis

Urinalysis interpretation requires systematic evaluation of three components—physical examination, chemical dipstick testing, and microscopic examination—which must be interpreted together in the context of clinical symptoms, never in isolation. 1

Specimen Collection and Handling

• Obtain a midstream clean-catch specimen in cooperative adults, or use catheterization/suprapubic aspiration in infants, young children, or women unable to provide clean specimens to avoid contamination. 1, 2
• Process the specimen within 1 hour at room temperature or 4 hours if refrigerated, as urine is unstable and composition changes begin immediately after voiding. 2, 3
• High epithelial cell counts indicate contamination—if present, repeat collection with proper technique before making clinical decisions. 2

Physical Examination Parameters

• Assess color, clarity, volume, and specific gravity as the initial step. 4, 3
• Cloudy urine typically results from precipitated phosphate crystals in alkaline urine, though pyuria is also possible. 5
• Strong odor may indicate concentrated urine rather than infection—do not diagnose UTI based on odor alone. 5
• Specific gravity provides reliable assessment of hydration status (normal range 1.005-1.030). 5

Chemical Dipstick Testing: Systematic Approach

Leukocyte Esterase

• Sensitivity: 83-94% when UTI is clinically suspected; Specificity: 78%. 1
• A positive result indicates pyuria but requires clinical correlation with symptoms—never diagnose UTI on dipstick alone. 2
• Negative leukocyte esterase has excellent negative predictive value (82-91%) and effectively rules out UTI in most populations. 2
• False-positives occur with contaminated specimens, oxidizing agents, and certain medications. 2
• False-negatives occur with high urinary glucose, high specific gravity, or certain antibiotics. 2

Nitrite Test

• Sensitivity: 49-53% (poor); Specificity: 98-100% (excellent). 1
• A positive nitrite is highly specific for gram-negative bacteria (E. coli, Proteus, Klebsiella) but negative results do not rule out UTI. 1, 2
• Low sensitivity is particularly problematic in infants/children who void frequently, as bacteria need 4+ hours in bladder to convert nitrates to nitrites. 2

Combined Testing Strategy

• Leukocyte esterase OR nitrite positive: Sensitivity 88-93%, Specificity 72-79%. 1
• Both leukocyte esterase AND nitrite negative: Effectively rules out UTI with 90.5% negative predictive value. 2

Hematuria Detection

• Dipstick-positive hematuria (trace or greater) must be confirmed with microscopic examination—dipstick alone is insufficient. 1, 6
• Dipstick measures peroxidase activity and produces false-positives with hemoglobinuria, myoglobinuria, povidone-iodine, and certain medications. 6

Other Dipstick Parameters

• pH: Normal range 4.5-8.0; alkaline urine (pH >7.5) may indicate urease-producing organisms like Proteus. 2
• Protein: Positive results require evaluation with clinical context, renal function, and microscopic findings. 7
• Glucose, ketones, bilirubin, urobilinogen: Evaluate based on clinical suspicion of metabolic or hepatobiliary disease. 4, 3

Microscopic Examination: Critical Thresholds

White Blood Cells (Pyuria)

• ≥5 WBCs per high-power field (HPF) defines pyuria: Sensitivity 73-90%, Specificity 81-86%. 1
• ≥10 WBCs/HPF is the threshold used in most clinical guidelines for UTI diagnosis. 2
• Pyuria alone does NOT indicate infection—asymptomatic bacteriuria with pyuria is common (15-50% prevalence in elderly) and should NOT be treated. 2

Red Blood Cells (Hematuria)

• ≥3 RBCs/HPF defines microscopic hematuria. 1, 6
• Document microscopic hematuria in 2 of 3 properly collected specimens before initiating full evaluation. 1, 6
• Gross hematuria requires urgent evaluation due to 7.2 odds ratio for urologic cancer. 6

Bacteria

• Presence of bacteria on Gram stain of uncentrifuged urine correlates with ≥10⁵ CFU/mL (Sensitivity 91-96%, Specificity 96%). 2
• Mixed bacterial flora indicates contamination, not infection—repeat collection with proper technique. 2

Epithelial Cells, Crystals, and Casts

• High epithelial cell counts indicate contamination—repeat specimen collection. 2
• Crystals: Interpret based on urine pH and clinical context (e.g., calcium oxalate, uric acid, struvite). 4
• Casts: Presence indicates renal parenchymal disease; type of cast (RBC, WBC, granular, hyaline) guides differential diagnosis. 4

Clinical Application: UTI Diagnosis Algorithm

Step 1: Assess for Specific Urinary Symptoms

• Required symptoms: Dysuria, frequency, urgency, fever, or gross hematuria. 2
• Do NOT diagnose UTI based on non-specific symptoms alone (confusion, falls, cloudy/smelly urine) in elderly patients. 2
• If asymptomatic: Do NOT order urinalysis or culture—asymptomatic bacteriuria should not be screened for or treated. 2

Step 2: Interpret Urinalysis Results in Context

If BOTH leukocyte esterase AND nitrite are NEGATIVE:

• UTI is effectively ruled out—no further testing needed. 2

If EITHER leukocyte esterase OR nitrite is POSITIVE + symptoms present:

• In healthy, non-pregnant adults with uncomplicated cystitis: Treat empirically without culture. 2
• In febrile infants <2 years, suspected pyelonephritis, recurrent UTIs, or complicated cases: Obtain urine culture before starting antibiotics. 2

If pyuria present WITHOUT symptoms:

• Do NOT treat—this represents asymptomatic bacteriuria. 2

Step 3: Culture Interpretation

• Diagnostic threshold for UTI: ≥50,000 CFU/mL of single uropathogen from catheterized/suprapubic specimen in pediatric patients. 1
• Mixed genital flora indicates contamination—repeat collection, do NOT treat. 6

Clinical Application: Hematuria Evaluation Algorithm

Step 1: Confirm Microscopic Hematuria

• Dipstick-positive must be confirmed with microscopy showing ≥3 RBCs/HPF. 1, 6
• Document in 2 of 3 properly collected specimens before proceeding to evaluation. 1

Step 2: Risk Stratification

High-risk patients require full urologic evaluation after single positive UA: 1, 6

• Age >40 years
• Smoking history
• History of gross hematuria
• Occupational exposure to chemicals/dyes
• History of urologic disorders

Low-risk patients:

• Confirm persistence on repeat testing before urologic referral. 1

Special Population Considerations

Pediatric Patients (2-24 months with fever)

• Require urine culture even with negative dipstick (10-50% of UTIs have false-negative urinalysis). 2
• Preferred collection: Catheterization or suprapubic aspiration—bag specimens have only 15% positive predictive value. 1, 2
• Diagnostic criteria: Pyuria and/or bacteriuria on urinalysis AND ≥50,000 CFU/mL of single uropathogen on culture. 1

Elderly/Long-Term Care Patients

• Do NOT screen for or treat asymptomatic bacteriuria (prevalence 15-50% in this population). 2
• Evaluate only with acute onset of specific urinary symptoms: Dysuria, frequency, urgency, fever, or costovertebral angle tenderness. 1, 2
• Do NOT diagnose UTI based on: Confusion, falls, delirium, cloudy/smelly urine alone. 2

Catheterized Patients

• Do NOT screen for or treat asymptomatic bacteriuria—reserve testing for symptomatic patients with fever, hypotension, or specific urinary symptoms. 2

Critical Pitfalls to Avoid

• Never diagnose UTI on urinalysis alone without symptoms—this leads to overtreatment of asymptomatic bacteriuria and antimicrobial resistance. 2
• Never rely solely on dipstick without microscopic confirmation for hematuria evaluation. 1, 6
• Never treat contaminated specimens (high epithelial cells, mixed flora)—repeat collection instead. 2
• Never attribute hematuria solely to anticoagulation without further investigation in high-risk patients. 6
• Discontinue phenazopyridine (Azo dyes) at least 48-72 hours before urinalysis—it causes false-positive and false-negative results across multiple parameters. 6
• Never delay urine culture collection in febrile infants, suspected pyelonephritis, or recurrent UTIs—always obtain before starting antibiotics. 2