Differential Diagnosis: Greenish Urine

1. Medications (Most Common Cause)

2. Infections

• Pseudomonas aeruginosa UTI or bacteremia - the classic infectious cause. The bacterium produces pyocyanin (a blue-green pigment) and pyoverdin, giving urine a distinct green color. Often accompanied by cloudy urine and UTI symptoms.

3. Bile Pigments / Hepatobiliary Disease

• Obstructive jaundice (cholestasis) - bilirubin and especially biliverdin (oxidized bilirubin) accumulates and is excreted in urine. In severe chronic obstruction, urine can turn dark green. Shaking the specimen produces a characteristic yellow foam.
• Severe hepatocellular disease

4. Dietary / Dyes

• Food dyes (especially blue and green artificial dyes in drinks, candies, sweets)
• Asparagus - can add a greenish tinge
• Chlorophyll supplements or products (e.g., Clorets gum with actizol)
• Traditional Chinese medicine (some preparations, e.g., Wilisan pills, contain methylene blue)

5. Rare Inherited / Metabolic Conditions

6. Structural / Anatomical

• Vesicoenteric fistula - bowel contents (including bile) mix with urine, producing green discoloration

Clinical Approach

In the vast majority of cases, green urine is drug-induced and benign, resolving spontaneously once the offending agent is stopped. Infection and biliary causes require prompt evaluation.

Workup to Rule Out Hepatobiliary Disease vs. Pseudomonas UTI

Part 1 - Ruling Out Hepatobiliary Disease

Step 1 - Urine Dipstick

• Urine bilirubin - detects conjugated (direct) bilirubin only. Unconjugated bilirubin is albumin-bound and does not pass into urine. A positive urine bilirubin immediately points to hepatobiliary pathology (cholestasis, hepatocellular disease, or biliary obstruction).
• A simple bedside clue: shaking the urine specimen produces yellow foam (vs. white foam in concentrated normal urine).

Step 2 - Serum Liver Function Tests

Step 3 - Fractionated Bilirubin Interpretation

• Predominantly conjugated hyperbilirubinemia narrows to: extrahepatic cholestasis (bile duct stones, strictures), intrahepatic cholestasis (viral hepatitis, alcoholic hepatitis, PBC, drugs/toxins, sepsis), or defective canalicular transport.
• Predominantly unconjugated points away from cholestasis toward hemolysis or conjugation defects. - Yamada's Textbook of Gastroenterology, 7e

Step 4 - Abdominal Imaging

• Abdominal ultrasound is the first-line imaging test - it identifies bile duct dilation (>7 mm = abnormal), gallstones, biliary strictures, and liver parenchymal changes. Note: the bile duct may NOT be dilated early in acute obstruction. - Harrison's Principles of Internal Medicine, 22e
• If ultrasound is inconclusive: MRCP (best non-invasive biliary imaging) or CT abdomen for suspected malignancy/mass.
• ERCP is reserved for cases where therapeutic intervention (stone removal, stenting) is anticipated.

Part 2 - Ruling Out Pseudomonas UTI

Step 1 - Urinalysis with Microscopy

A positive nitrite test makes UTI very likely (specificity 98%), but nitrite testing has insufficient sensitivity alone (53%) and is typically negative in Pseudomonas. - Tintinalli's Emergency Medicine

Step 2 - Urine Culture and Sensitivity (Gold Standard)

• Culture results must always be interpreted in the context of pyuria - a positive culture without pyuria may represent colonization rather than true infection.
• Sensitivity testing from the culture will also guide antibiotic choice, important because Pseudomonas has intrinsic resistance to many antibiotics. - Tintinalli's Emergency Medicine

Step 3 - Blood Cultures (if systemically unwell)

• If the patient has fever, rigors, hypotension, or other signs of sepsis, add blood cultures to rule out Pseudomonas bacteremia - this is a clinical emergency.

Summary: Quick Differentiation at the Bedside