Are blood cultures recommended for patients with noninfective kidney stones?

Blood Cultures Are Not Recommended for Noninfective Kidney Stones

Blood cultures should not be obtained in patients with noninfective kidney stones as they provide no clinical benefit and may lead to unnecessary antibiotic use.

Rationale for Not Obtaining Blood Cultures

Clinical Indications for Blood Cultures

Blood cultures are specifically indicated when there is suspicion of bloodstream infection, which is not present in noninfective kidney stones. According to guidelines, blood cultures should be obtained when there are specific signs suggesting bacteremia:

• Fever, chills, or hypothermia
• Leukocytosis, left-shift of neutrophils, or neutropenia
• Signs of hemodynamic compromise
• Hypoalbuminemia or development of renal failure when infection is suspected 1

Evidence Against Routine Blood Cultures in Noninfective Stones

The European Society of Clinical Microbiology and Infectious Diseases (ESCMID) guidelines indicate that even in urinary tract infections with systemic symptoms, blood cultures have limited impact on treatment:

• In patients with pyelonephritis, relevant pathogens were found in only 0-2.4% of blood cultures that were not found in urine cultures
• These findings did not lead to changes in antibiotic treatment in any patients 1

When Blood Cultures ARE Indicated in Urolithiasis

Blood cultures should be considered in the following scenarios:

1. Obstructive pyelonephritis - Kidney stones causing obstruction with signs of infection (fever, pyuria, positive urine culture) 2

2. Infected stones - Stones formed due to urease-producing bacteria or secondarily infected stones 2, 3

3. Signs of sepsis - When a patient with kidney stones presents with:

   • Fever >38°C or <36°C
   • Heart rate >90 beats/minute
   • Respiratory rate >20 breaths/minute
   • White blood cell count >12,000/μL or <4,000/μL 1

Diagnostic Approach for Kidney Stones

Recommended Tests for Noninfective Kidney Stones

1. Urinalysis - To assess for hematuria (≥5 RBC/HPF) 4
2. Urine culture - Only if pyuria (>10 WBC/HPF) is present 4
3. Imaging - CT scan, ultrasound, or X-ray KUB to confirm stone presence and location

When to Consider Infection

Pyuria was found in 14.2% of patients with renal colic. Among patients with pyuria, 36.4% had positive urine cultures compared to only 3.3% of patients without pyuria 4. The risk of positive culture increases with:

• Increasing pyuria (60% positive cultures with >50 WBC/HPF)
• Increased leukocyte esterase on dipstick 4

Common Pitfalls to Avoid

1. Unnecessary "pan-culturing" - The Surviving Sepsis Campaign discourages "pan culture" of all potential sites when the source of infection is not clinically apparent, as this can lead to inappropriate antimicrobial use 1

2. Delaying treatment in true sepsis - If a patient with kidney stones shows signs of sepsis, blood cultures should be obtained quickly (within 45 minutes) but should not delay antimicrobial therapy 1

3. Misinterpreting contaminants - False-positive blood cultures can lead to unnecessary antibiotic use and prolonged hospitalization 1

4. Missing occult infection - In rare cases, infection stones may be caused by difficult-to-culture organisms like Ureaplasma urealyticum and Corynebacterium urealyticum 5

By following these evidence-based recommendations, clinicians can avoid unnecessary blood cultures in patients with noninfective kidney stones while ensuring appropriate diagnostic workup for those with suspected infection.