What are the causes and treatments of pyuria (presence of pus in the urine)?

Causes of Pyuria

Pyuria (presence of pus in urine) is primarily caused by urinary tract infections, but can also occur in non-infectious conditions and should not be treated unless accompanied by symptoms and significant bacteriuria. 1, 2

Definition and Significance

Pyuria is defined as the presence of increased numbers of polymorphonuclear leukocytes in the urine, indicating an inflammatory response in the urinary tract. Significant pyuria thresholds include:

• ≥10 WBCs/mm³ on enhanced urinalysis
• ≥5 WBCs/hpf on centrifuged specimen
• Positive leukocyte esterase on dipstick 1, 2

Infectious Causes of Pyuria

1. Urinary Tract Infections (UTIs)

• Bacterial cystitis: Inflammation of the bladder typically presenting with dysuria, urgency, and suprapubic pain 1
• Pyelonephritis: Kidney inflammation with systemic symptoms like fever and flank pain 1
• Complicated UTIs: Involving catheters, structural abnormalities, or immunosuppression 1

Common Uropathogens:

• Escherichia coli (most common, ~80% of cases) - strongly associated with pyuria 3
• Klebsiella species - may cause UTI with less pronounced pyuria 3
• Enterobacter species 4
• Proteus mirabilis and Proteus vulgaris 4
• Enterococcus species - often associated with less pyuria 3

2. Other Infectious Causes

• Chlamydia trachomatis infection (may present with pyuria without significant bacterial growth on standard cultures) 5
• Tuberculosis of the urinary tract
• Renal abscess

Non-Infectious Causes of Pyuria

1. Inflammatory Conditions

• Interstitial nephritis
• Interstitial cystitis/bladder pain syndrome
• Kawasaki disease 1

2. Structural/Mechanical Causes

• Kidney stones/urolithiasis
• Foreign bodies (including indwelling catheters) 6

3. Other Causes

• Chemical urethritis 1
• Streptococcal infections (non-urinary source) 1
• Genitourinary tumors
• Recent urologic procedures

Special Considerations

Asymptomatic Bacteriuria with Pyuria

• Common in certain populations (elderly, catheterized patients)
• Should not be treated with antibiotics unless in specific high-risk groups (pregnant women, patients undergoing urologic procedures) 1, 2
• Treatment of asymptomatic bacteriuria can lead to antimicrobial resistance and adverse drug effects 1

Catheter-Associated Pyuria

• Pyuria is less strongly correlated with infection in catheterized patients than in non-catheterized patients 6
• Most strongly associated with gram-negative infections; weaker association with gram-positive cocci or yeast infections 6
• Pyuria with WBC >10/μL has 90% specificity but only 37% sensitivity for catheter-associated UTI 6

Pediatric Considerations

• In children, pyuria without bacteriuria is insufficient for UTI diagnosis as it can occur in non-infectious conditions 1
• Bacteriuria without pyuria may indicate contamination or asymptomatic bacteriuria 1
• Absence of pyuria doesn't exclude UTI, particularly with Klebsiella and Enterococcus infections 3

Diagnostic Approach

1. Urinalysis:

   • Leukocyte esterase test (sensitivity ~83-94%)
   • Nitrite test (high specificity but lower sensitivity)
   • Microscopic examination for WBCs and bacteria 1

2. Urine Culture:

   • Gold standard for UTI diagnosis
   • Significant growth typically defined as ≥50,000 CFU/mL in catheterized specimens or ≥105 CFU/mL in voided specimens 1, 7
   • In symptomatic women, even growth as low as 102 CFU/mL could reflect infection 7

3. Correlation with Symptoms:

   • Pyuria alone should not trigger antibiotic treatment without symptoms 2
   • Non-specific symptoms in elderly (confusion, low-grade fever) should not be attributed to UTI based on pyuria alone 2

Treatment Considerations

Treatment should be directed at the underlying cause:

1. For UTIs:

   • First-line options: nitrofurantoin, fosfomycin, or trimethoprim-sulfamethoxazole (when local resistance <20%) 7
   • Duration: 3 days for uncomplicated cystitis; 7-14 days for pyelonephritis 8
   • Consider local resistance patterns when selecting empiric therapy 7

2. For Non-Infectious Causes:

   • Address underlying condition (remove foreign body, treat inflammatory disorder)
   • Symptomatic management as appropriate

3. When Not to Treat:

   • Asymptomatic bacteriuria/pyuria in most populations 1, 2
   • Pyuria without significant bacteriuria in asymptomatic individuals 2

Clinical Pitfalls to Avoid

1. Overdiagnosis and Overtreatment:

   • Treating pyuria without symptoms leads to unnecessary antibiotic use
   • Treating asymptomatic bacteriuria can increase antimicrobial resistance

2. Misinterpretation of Urinalysis:

   • Pyuria is not specific for UTI and occurs in many non-infectious conditions
   • Absence of pyuria doesn't rule out UTI, especially with certain pathogens

3. Inadequate Specimen Collection:

   • Contaminated specimens can lead to false-positive results
   • For catheterized patients, consider changing the catheter before specimen collection 2

4. Failure to Consider Alternative Diagnoses:

   • In patients with pyuria but negative cultures, consider atypical pathogens or non-infectious causes

By understanding the diverse causes of pyuria and their appropriate management, clinicians can avoid unnecessary antibiotic use while ensuring proper treatment for true infections.