What are the differential diagnoses for dark-colored urine?

Differential Diagnosis for Dark-Colored Urine

Start with urinalysis with dipstick and microscopy immediately to narrow the differential diagnosis, as this single test can distinguish between the most common pathologic causes including hepatobiliary disease, hemoglobinuria, myoglobinuria, and glomerular pathology. 1

Initial Clinical Assessment

Before ordering tests, evaluate these key clinical features:

• Assess hydration status first - concentrated urine from dehydration is the most common benign cause, identifiable by elevated urine specific gravity (>1.020) and history of inadequate fluid intake 2, 1

• Complete medication review including prescription drugs, over-the-counter supplements, and herbal products, as medications are the second most common benign cause of dark urine 1, 3

• Screen for red flag symptoms that indicate urgent pathology:

  • Fever, jaundice, or right upper quadrant pain → hepatobiliary disease 2
  • Muscle pain, weakness, or tenderness → rhabdomyolysis with myoglobinuria 2
  • Altered mental status or hemodynamic instability → requires urgent evaluation 2

Laboratory-Based Diagnostic Algorithm

Step 1: Urinalysis Interpretation

If bilirubin-positive on dipstick:

• Indicates hepatobiliary disease requiring liver function tests and hepatobiliary imaging 2, 1
• This finding mandates urgent evaluation if accompanied by fever, jaundice, or right upper quadrant pain 2

If blood-positive on dipstick WITHOUT RBCs on microscopy:

• Suggests hemoglobinuria or myoglobinuria 2, 1
• Check creatine kinase to distinguish: elevated CK indicates myoglobinuria from rhabdomyolysis 1
• If muscle symptoms present (pain, weakness, tenderness), treat as rhabdomyolysis urgently 2

If proteinuria with red blood cell casts and dysmorphic RBCs (>80%):

• Indicates glomerular pathology requiring nephrology referral 1
• This pattern suggests glomerulonephritis and warrants urgent specialist evaluation 1

If elevated specific gravity (>1.020) with otherwise normal dipstick:

• Confirms concentrated urine from dehydration 1
• Recommend increased fluid intake and reassess 2

Imaging Strategy

• Renal ultrasound is the initial imaging modality to assess kidney size, echogenicity, rule out hydronephrosis, and differentiate acute from chronic kidney disease 1

• CT urography (without and with IV contrast) provides comprehensive evaluation if concern exists for obstruction, mass, or structural pathology 1

Mandatory Nephrology Referral Criteria

Refer immediately if any of the following are present:

• Proteinuria >1,000 mg/24 hours or significant albuminuria 1
• Red cell casts or >80% dysmorphic RBCs suggesting glomerulonephritis 1
• Acute-on-chronic kidney disease with active sediment 1
• eGFR <30 mL/min/1.73 m² or rapid decline in kidney function 1

Common Pitfalls to Avoid

• Do not dismiss dark urine as benign without urinalysis - while medications and dehydration are common, life-threatening conditions like infection and poisonings can also manifest as urine discoloration 3, 4

• Do not rely on patient-reported color alone - gross examination by the clinician combined with dipstick testing is essential, as patient descriptions can be unreliable 5, 6

• Do not overlook occupational and environmental exposures to chemicals or toxins that can cause urine discoloration 1