What causes milky urine?

Causes of Milky Urine

The most common cause of milky urine is chyluria, which results from an abnormal communication between the lymphatic system and urinary tract, allowing lymphatic fluid (chyle) to enter the urine. 1, 2, 3

Primary Causes of Milky Urine

1. Chyluria

• Definition: Presence of chyle (lymphatic fluid) in urine due to lymphatic-urinary fistula

• Etiologies:

  • Parasitic (most common globally):

    • Filariasis (Wuchereria bancrofti) - predominant in Asia, especially India, China, and Taiwan 2, 3
    • Other parasites: echinococcosis, cysticercosis 4

  • Non-parasitic (more common in Western countries):

    • Congenital lymphatic malformations
    • Retroperitoneal lymphatic dysplasia 5
    • Trauma or surgical injury to lymphatics
    • Aortic aneurysm
    • Pregnancy
    • Granulomatous diseases (tuberculosis, leprosy, fungal infections)
    • Malignancy 3, 4

• Diagnostic features:

  • Milky white urine (especially post-meal)
  • Positive urine ether test (clears with ether)
  • Elevated urine triglycerides (mean 37.2 ± 24.6 mg%) 2
  • Proteinuria (median 24-hour protein 4.96g) 2
  • Negative urine leukocyte test despite leukocyturia 5

2. Nephrotic Syndrome

• Proteinuria with lipiduria can cause milky appearance
• Minimal change disease has been reported as a cause 2
• Distinguished from chyluria by:
  • Negative urine ether test
  • Absence of triglycerides in urine
  • Presence of other nephrotic features (hypoalbuminemia, edema, hyperlipidemia)

3. Pyuria

• Urinary tract infection with significant white blood cells
• Usually appears cloudy rather than truly milky
• Positive leukocyte esterase test
• Bacteria present on microscopy or culture 6

4. Phosphaturia

• Precipitation of phosphate crystals in alkaline urine
• More common in patients with urinary tract infections caused by urea-splitting bacteria 6
• Clears with acidification of urine

Diagnostic Approach

Initial Evaluation:

1. Urinalysis with microscopy:

   • Check for protein, triglycerides, red blood cells, white blood cells, bacteria, and crystals 1
   • Urine ether test: milky appearance clears with ether in chyluria

2. Quantitative measurements:

   • 24-hour urine protein excretion
   • Urine triglyceride levels 2

3. Blood tests:

   • Complete blood count
   • Renal function tests
   • Serum albumin
   • Lipid profile
   • Rapid filarial antigen test (in endemic areas) 2

Advanced Imaging:

1. Ultrasonography: Initial imaging to rule out structural abnormalities 2

2. CT Urography: For patients with hematuria or suspected anatomical abnormalities 6, 1

3. MRI Abdomen: To identify dilated lymphatics 2

   • Patients with dilated lymphatics have significantly higher proteinuria (8.15 ± 2.55g vs 4.64 ± 0.70g) 2

4. Lymphangiography: Gold standard for identifying lymphatic-urinary fistula 4, 5

   • Bipedal lymphangiography
   • CT-lymphangiogram

5. Cystoscopy: Can identify which ureter is producing milky urine 4

Management Approach

1. Chyluria Management:

• Conservative measures:

  • Low-fat diet with medium-chain triglycerides
  • High protein diet to compensate for losses
  • Fat-soluble vitamin supplementation 7

• Medical management:

  • Antifilarial drugs for parasitic etiology (diethylcarbamazine)
  • Nutritional support for protein losses 7

• Sclerotherapy:

  • For cases not responding to medical management
  • Agents: 50% dextrose and 0.2% povidone iodine 2
  • Studies show non-filarial cases more frequently require sclerotherapy 2

• Surgical intervention:

  • Reserved for refractory cases
  • Renal pelvic instillation of sclerosing agents
  • Surgical ligation of lymphatic-urinary connections 7

2. Nephrotic Syndrome Management:

• Treat according to underlying cause
• Renal biopsy may be indicated 2

3. Urinary Tract Infection Management:

• Appropriate antibiotics based on culture and sensitivity
• For complicated UTIs with systemic symptoms:
  • Amoxicillin plus aminoglycoside
  • Second-generation cephalosporin plus aminoglycoside
  • IV third-generation cephalosporin 6

Clinical Pearls and Pitfalls

• Age consideration: Filarial chyluria typically presents at a younger age (mean 22.9 ± 4.5 years) compared to non-filarial causes (mean 31.5 ± 4.8 years) 2

• Geographical context: In Asia, particularly India, China, and Taiwan, parasitic causes predominate; in Western countries, non-parasitic etiologies are more common 3

• Nutritional concerns: Persistent chyluria can lead to significant protein loss, malnutrition, weight loss, and immunosuppression 7

• Referral indications:

  • Nephrology: For significant proteinuria (>1g/day) or declining renal function 1
  • Urology: For hematochyluria or when surgical intervention is considered 1

• Follow-up: Regular monitoring of renal function and 24-hour urine protein and triglyceride levels is essential 2