What is the initial workup for a patient presenting with dark urine?

Initial Workup for Dark Urine

The initial workup for dark urine should include a complete urinalysis with microscopic examination, urine culture, complete blood count, and renal function tests to differentiate between hematuria, hemoglobinuria, and myoglobinuria. 1

Initial Assessment and Differentiation

1. Confirm true hematuria vs. other causes of dark urine:

   • Distinguish between hematuria (≥3 RBCs per high-power field), hemoglobinuria, and myoglobinuria 1
   • Perform dipstick test and microscopic examination:
     • Positive blood on dipstick with RBCs on microscopy = hematuria
     • Positive blood on dipstick without RBCs = hemoglobinuria or myoglobinuria
     • Positive blood on dipstick with brownish granular casts = myoglobinuria 2

2. Rule out benign causes:

   • Recent vigorous exercise
   • Menstruation in women
   • Recent trauma or procedures
   • Current urinary tract infection (confirm with urine culture)
   • Medication or food-related discoloration 1
   • Note: Antiplatelet or anticoagulant therapy is NOT considered a satisfactory explanation for hematuria 1

Laboratory Evaluation

• Complete urinalysis with microscopic examination
• Urine culture to rule out infection
• Complete blood count to assess for systemic disease
• Renal function tests (BUN, creatinine) 1
• If hemoglobinuria is suspected: LDH, haptoglobin, bilirubin 2
• If myoglobinuria is suspected: CK levels 3

Risk Stratification

Categorize patients into risk groups based on:

High-risk factors:

• Age (women ≥50 years, men ≥40 years)
• Smoking history >30 pack-years
• Gross hematuria or >25 RBC/HPF
• History of pelvic radiation
• Chronic urinary infections
• Occupational exposures (dyes, chemicals) 1

Additional concerning features:

• Irritative voiding symptoms
• Current or past tobacco use
• Chemical exposures 4

Imaging Studies Based on Risk

1. High-risk patients:

   • Multi-phasic CT urography (without and with IV contrast) is the imaging procedure of choice 4
   • Includes sufficient phases to evaluate renal parenchyma and excretory phase for upper tract urothelium 4

2. Special circumstances:

   • Renal insufficiency or contrast allergy: MR urography or ultrasound 1
   • Young, low-risk patients: Renal ultrasound may be sufficient 1

Cystoscopic Evaluation

• Perform cystoscopy in all patients aged 35 years and older with asymptomatic microhematuria (AMH) 4
• May be performed at physician's discretion in patients younger than 35 years 4
• Must be performed regardless of age in patients with risk factors for urinary tract malignancies 4

Follow-up Recommendations

• If AMH persists after negative urologic workup, conduct yearly urinalyses 4
• If a patient with persistent AMH has two consecutive negative annual urinalyses, no further evaluation for AMH is necessary 4
• For persistent or recurrent AMH after initial negative workup, consider repeat evaluation within 3-5 years 4

Common Pitfalls to Avoid

1. Assuming a benign cause without complete evaluation in high-risk patients 1
2. Inadequate imaging (using ultrasound alone in high-risk patients) 1
3. Dismissing microscopic hematuria in patients with overactive bladder symptoms 1
4. Confusing hemoglobinuria with hematuria, leading to unnecessary urologic workup 2
5. Delays in evaluation (>9 months) in patients with hematuria can be associated with decreased survival if malignancy is present 1

Remember that dark urine can be caused by various conditions beyond hematuria, including hemoglobinuria (from hemolysis), myoglobinuria (from rhabdomyolysis), medications, foods, and metabolic disorders 5, 6. Proper differentiation at the initial assessment is crucial for directing appropriate further workup.