From the Guidelines
If a urine dipstick test is completely normal, it is not necessary to send the sample for formal culture in most cases, as a normal dipstick has a high negative predictive value for urinary tract infection (UTI). This approach is supported by the European Association of Urology guidelines on urological infections, which state that urine analysis leads to only a minimal increase in diagnostic accuracy in patients presenting with typical symptoms of uncomplicated cystitis 1. However, there are specific situations where culture may still be warranted despite a normal dipstick, such as in patients with recurrent UTIs, pregnant women, immunocompromised individuals, those with urological abnormalities, patients with persistent symptoms despite a negative dipstick, or in cases where there is clinical suspicion for complicated UTI.
Key Considerations
- A normal urine dipstick test has a high negative predictive value for UTI, making it unlikely that a UTI is present if the dipstick is negative 1.
- Urine culture remains the gold standard for diagnosing UTIs, as it can detect bacterial growth even when dipstick parameters are normal.
- Culture provides antimicrobial susceptibility data, which guides appropriate antibiotic selection, particularly important in complicated cases or when antibiotic resistance is a concern.
- The Infectious Diseases Society of America recommends that urinalysis and urine cultures should not be performed for asymptomatic residents, and that the diagnostic laboratory evaluation of suspected UTI should be reserved for those with acute onset of UTI-associated symptoms and signs 1.
Specific Situations Where Culture May Be Warranted
- Patients with recurrent UTIs
- Pregnant women
- Immunocompromised individuals
- Those with urological abnormalities
- Patients with persistent symptoms despite a negative dipstick
- Cases where there is clinical suspicion for complicated UTI
- Suspected acute pyelonephritis
- Symptoms that do not resolve or recur within 4 weeks after completion of treatment
- Women who present with atypical symptoms 1.
From the Research
Urine Culture Necessity
- A formal urine culture may not be necessary if the urine dipstick test results are normal, but it depends on the patient's symptoms and pretest probability of urinary tract infection (UTI) 2.
- In patients with a high probability of UTI based on symptoms, negative dipstick urinalysis does not rule out UTI, and urine culture should be performed 2.
- Urine culture is the gold standard for detection of UTI, but asymptomatic bacteriuria is common, particularly in older women, and should not be treated with antibiotics 2.
Dipstick Urinalysis vs. Urine Culture
- Dipstick urinalysis is popular for its availability and usefulness, but results must be interpreted in context of the patient's pretest probability based on symptoms and characteristics 2.
- Nitrites are likely more sensitive and specific than other dipstick components for UTI, particularly in the elderly 2.
- Positive dipstick testing is likely specific for asymptomatic bacteriuria in pregnancy, but urine culture is still the test of choice 2.
- A study found that urine dipstick test had a sensitivity of 0.79 and specificity of 0.39, while urinalysis had a sensitivity of 0.95 and specificity of 0.21 3.
Clinical Presentation and Performance of Urine Dipstick
- Distinguishing symptomatic UTI from asymptomatic bacteriuria is problematic, as older adults are less likely to present with localized urinary symptoms 4.
- A study found that positive urine dipstick test for leukocytes and/or nitrites had high sensitivity (92%), but low specificity (50%) in the diagnosis of UTI in geriatric population 4.
- Negative predictive value of urine dipstick test was high (91%), suggesting that negative dipstick tests can suggest an absence of UTI 4.