From the Guidelines
A urinary tract infection (UTI) is still possible even with negative nitrites on urinalysis. While positive nitrites strongly suggest a UTI, their absence doesn't rule one out, as the nitrite test has lower sensitivity or true-negative results 1. Approximately, the presence of either nitrite or leukocyte esterase has a sensitivity or true-positive rate of 88% for urinary tract infection, implying that a significant portion of UTIs may not be detected by the nitrite test alone 1. Other urinalysis findings like positive leukocyte esterase, presence of white blood cells, or bacteria on microscopy may still indicate infection.
- Clinical symptoms such as dysuria, frequency, urgency, and suprapubic pain remain important diagnostic factors.
- If symptoms are present despite negative nitrites, further evaluation may be warranted, including urine culture to identify the causative organism.
- Some UTIs may require empiric antibiotic treatment based on symptoms alone, typically with medications like nitrofurantoin, trimethoprim-sulfamethoxazole, or fosfomycin for uncomplicated cases, while awaiting culture results. The finding of clear urine on visual inspection had a negative predictive value of 97%, which can be useful in ruling out UTI, but not in confirming it 1.
From the Research
Urinary Tract Infection Diagnosis
- The diagnosis of urinary tract infections (UTIs) can be complex, and predicting the probability of UTIs through symptoms and test results is challenging 2.
- Dipstick urinalysis is a popular diagnostic tool, but results must be interpreted in the 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.
Negative Nitrites and UTI
- A negative dipstick urinalysis, including negative nitrites, does not rule out UTI, especially in patients with a high probability of UTI based on symptoms 2.
- The absence of urinary nitrite should not affect routine empiric antibiotic choice for presumptive UTI in young children, as the prevalence of enterococcal UTI is low 3.
- In cases where the probability of UTI is moderate or unclear, urine culture should be performed, as it is the gold standard for detection of UTI 2.
Antibiotic Choice and Nitrite Results
- Emergency physicians should not adjust antibiotic therapy for UTI based on nitrite results, as there is no statistically significant difference in the proportion of isolates sensitive to trimethoprim/sulfamethoxazole between nitrite-positive and nitrite-negative groups 4.
- First-line treatments for UTI include nitrofurantoin, fosfomycin, and trimethoprim-sulfamethoxazole, which have minimal collateral damage and resistance 2, 5.
- The choice of antibiotic should be based on individualized assessment of risk factors for resistance and regimen tolerability 5.