What does foam in the urine indicate and how is it treated?

Foam in Urine: Clinical Significance and Management

What Foamy Urine Indicates

Foamy urine is most commonly a sign of proteinuria, though approximately 80% of patients complaining of foamy urine do not have significant proteinuria. 1

Key Clinical Findings

• Among patients presenting with subjective foamy urine, only 20-22% have overt proteinuria (>300 mg/g creatinine), while an additional 10-12% may have microalbuminuria 1
• The presence of foam can also result from benign causes including concentrated urine from dehydration, rapid urination, or the presence of semen in the urine 2, 3
• False-positive impressions of proteinuria can occur with alkaline, dilute, or concentrated urine, as well as with gross hematuria or the presence of mucus 2

Risk Factors for Significant Proteinuria in Patients with Foamy Urine

When evaluating foamy urine, the following factors significantly increase the likelihood of true proteinuria: 1

• Elevated serum creatinine (strongest predictor)
• Elevated serum phosphate
• Diabetes mellitus
• Reduced estimated glomerular filtration rate (eGFR)
• Elevated blood urea nitrogen (BUN)
• Hyperglycemia

Diagnostic Approach

Initial Evaluation

Perform urinalysis with dipstick testing and microscopic examination as the first-line diagnostic test. 4, 3

• Dipstick urinalysis can detect proteinuria, but be aware of false-positives from concentrated urine, alkaline pH, or contamination 2, 3
• If dipstick is positive for protein, confirm with quantitative measurement 2

Quantitative Assessment

Use spot urine albumin-to-creatinine ratio (UACR) or protein-to-creatinine ratio rather than 24-hour urine collection. 4

• UACR is more convenient and potentially more accurate than 24-hour collections 4, 2
• First-morning urine specimen is preferred for UACR measurement 4
• Normal UACR is <30 mg/g creatinine 4

Additional Testing Based on Results

If proteinuria is confirmed (UACR ≥30 mg/g): 4

• Measure serum creatinine and calculate eGFR
• Check serum electrolytes, BUN, glucose, and lipid panel
• Assess for diabetes and hypertension
• Evaluate for signs of chronic kidney disease (CKD)

Treatment Approach

When Proteinuria is Absent or Minimal

If UACR is <30 mg/g and renal function is normal, reassure the patient that foamy urine is likely benign. 2, 1

• Address reversible causes: dehydration, concentrated urine, recent vigorous exercise 2
• No specific treatment is required for benign foamy urine 2

When Significant Proteinuria is Present

For albuminuria ≥300 mg/g, initiate renin-angiotensin system (RAS) blockade with ACE inhibitor or ARB to reduce proteinuria and slow CKD progression. 4

Specific Management Strategies:

• Target reduction: Aim to reduce urinary albumin by ≥30% to slow CKD progression 4
• Protein intake: Maintain dietary protein at 0.8 g/kg body weight per day for non-dialysis CKD stage G3 or higher 4
• Continue RAS blockade even with mild to moderate increases in serum creatinine (≤30%) if no volume depletion is present 4

Referral Indications

Refer to nephrology if: 4

• eGFR <30 mL/min/1.73 m²
• Continuously increasing albuminuria despite treatment
• Continuously decreasing eGFR
• Active urinary sediment (red/white blood cells, cellular casts)
• Rapidly increasing proteinuria or rapidly decreasing eGFR
• Nephrotic-range proteinuria (>3.5 g/day)

Common Pitfalls to Avoid

• Do not assume all foamy urine represents kidney disease – most cases are benign 1
• Do not rely solely on dipstick testing – confirm positive results with quantitative UACR 4, 2
• Do not delay evaluation in high-risk patients – those with diabetes, hypertension, elevated creatinine, or elevated phosphate require prompt assessment 1
• Do not overlook transient causes – fever, intense exercise, dehydration, and emotional stress can cause temporary proteinuria 2
• Do not use 24-hour urine collections routinely – spot UACR is more practical and equally reliable 4, 2