When is a reflex urine culture recommended for patients with symptoms suggestive of a urinary tract infection (UTI)?

Reflex Urine Culture Criteria

Reflex urine cultures should only be performed in patients with symptoms suggestive of a urinary tract infection (UTI), and should not be used for screening or surveillance in asymptomatic patients. 1, 2

Appropriate Criteria for Reflex Urine Culture

Symptomatic Patients

• Reflex urine cultures should be reserved for patients with acute onset of UTI-associated symptoms:
  • Dysuria
  • Increased urinary frequency
  • Urgency
  • Suprapubic pain
  • New or worsening urinary incontinence
  • Gross hematuria
  • Fever (in the absence of other sources)
  • Suspected bacteremia 1, 2

Laboratory Parameters

When urinalysis is performed in symptomatic patients, the following findings should trigger a reflex culture:

• Presence of pyuria (≥10 WBCs/high-power field)
• Positive leukocyte esterase test
• Positive nitrite test 1

Important Considerations

Avoid Testing in Asymptomatic Patients

• Asymptomatic bacteriuria is common (15-50% in non-catheterized long-term care facility residents and nearly 100% in those with chronic indwelling catheters) 1
• Screening urine cultures in asymptomatic patients should not be performed as they lead to unnecessary antibiotic use and promote antimicrobial resistance 1, 2

Special Populations

Catheterized Patients

• For patients with indwelling catheters and suspected UTI:
  • The catheter should be changed prior to specimen collection
  • Urine should be collected after allowing for accumulation while plugging the new catheter
  • Specimens should never be obtained from extension tubing or collection bag 1

Neurogenic Lower Urinary Tract Dysfunction (NLUTD) Patients

• Do not perform surveillance/screening urine cultures in asymptomatic NLUTD patients
• Only obtain urinalysis and urine culture in NLUTD patients with signs and symptoms suggestive of UTI 1

Benefits of Appropriate Reflex Culture Criteria

• Reduces laboratory workload by avoiding unnecessary cultures 3, 4
• Improves antimicrobial stewardship by reducing inappropriate antibiotic use 5
• Studies show significant decreases in urine culturing rates and reported rates of catheter-associated UTI following implementation of reflex protocols 4

Pitfalls to Avoid

• Relying solely on positive urine cultures without clinical correlation can lead to overtreatment of asymptomatic bacteriuria 1, 2
• The positive predictive value of reflex urine culture criteria varies (58% in one study), highlighting the importance of clinical correlation 6
• No single urinalysis parameter has both high sensitivity and high specificity for predicting bacteriuria 7
• The negative predictive value of pyuria is high (≥90%) in most patient populations except females aged ≥65 years and patients with indwelling catheters 7

Remember that diagnostic tests should only be performed if they have reasonable diagnostic yield, are low risk, reasonable in cost, and will improve patient management. If test results won't change the treatment strategy, there is little justification for ordering the test 1.