From the Guidelines
A urinary tract infection (UTI) is still possible even with negative nitrites on urinalysis. While the presence of nitrites is a strong indicator of a UTI, the absence of nitrites does not rule out the infection, as the sensitivity of the nitrite test is lower than its specificity 1. According to a meta-analysis, the presence of either nitrite or leukocyte esterase has a sensitivity of 88% for urinary tract infection, implying that about 12% of UTIs may be missed if relying solely on these tests 1. Some key points to consider in the diagnosis of UTI with negative nitrites on urinalysis include:
- The type of bacteria causing the UTI, as not all bacteria produce nitrate reductase, the enzyme that converts nitrates to nitrites 1
- The duration of bladder dwell time, which may affect the conversion of nitrates to nitrites 1
- Other urinalysis findings, such as positive leukocyte esterase, presence of white blood cells, or bacteria on microscopy, which can suggest a UTI despite negative nitrites 1
- Clinical symptoms, such as dysuria, frequency, urgency, and suprapubic pain, which remain important diagnostic factors In cases where symptoms strongly suggest a UTI, empiric treatment with antibiotics may be appropriate while awaiting urine culture results, which remain the gold standard for diagnosis 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.