Should a patient with a nitrite positive, leukocyte (white blood cell) negative urine test be treated for a urinary tract infection (UTI)?

Management of Nitrite Positive, Leukocyte Negative Urine Tests

A nitrite positive, leukocyte negative urine test should generally be treated for UTI, as a positive nitrite test has high specificity (92-100%) for bacteriuria, even in the absence of leukocytes. 1

Diagnostic Interpretation

The presence of nitrites in urine strongly indicates bacterial infection, particularly from gram-negative enteric bacteria that convert urinary nitrates to nitrites. According to clinical guidelines:

• Nitrite testing has high specificity (92-100%) but lower sensitivity (19-48%) 1
• The positive predictive value of nitrite testing is very high (96%) 2
• A positive nitrite test alone has a false positive rate of less than 4% 3

Significance of Negative Leukocyte Esterase

While pyuria (presence of white blood cells) typically accompanies UTI, its absence doesn't rule out infection:

• Up to 20% of febrile infants with documented pyelonephritis may not have pyuria on initial urinalysis 3
• Leukocyte esterase testing has higher sensitivity (72-97%) but lower specificity (41-86%) compared to nitrite testing 1

Treatment Decision Algorithm

1. Positive nitrite, negative leukocyte esterase:

   • Treat empirically for UTI
   • Collect urine culture before starting antibiotics
   • Consider patient symptoms and risk factors

2. Factors supporting treatment:

   • Presence of UTI symptoms (dysuria, frequency, urgency)
   • Risk factors for UTI complications
   • High specificity of nitrite test (low false positive rate)

3. Antibiotic selection:

   • First-line options include nitrofurantoin, trimethoprim-sulfamethoxazole, or fosfomycin 1
   • Adjust therapy based on culture results within 48-72 hours

Important Considerations

• Culture confirmation: A properly obtained urine specimen should be collected for culture before starting antibiotics 1
• Patient symptoms: The presence of symptoms increases the likelihood that a positive nitrite test represents true infection rather than contamination
• Risk of untreated UTI: Untreated UTIs can progress to pyelonephritis and potentially sepsis, with higher mortality rates than asymptomatic bacteriuria 1

Common Pitfalls

• Overreliance on leukocyte testing: Absence of leukocytes doesn't rule out UTI, as pyuria may be absent in up to 20% of confirmed infections 3
• Ignoring nitrite results: The high specificity of nitrite testing makes it a valuable indicator of bacteriuria, even when leukocyte esterase is negative
• Failing to obtain cultures: Treatment should ideally be preceded by urine culture collection to confirm the diagnosis and guide therapy 1

Special Populations

• Pediatric patients: In children under 2 years, only about 3% of nitrite-negative UTIs are caused by enterococci, so standard empiric antibiotic choices are appropriate regardless of nitrite status 4
• Elderly patients: Urine dipstick tests have lower specificity (20-70%) in elderly patients, requiring more careful interpretation 1

The high specificity and positive predictive value of nitrite testing support treating patients with positive nitrite results, even in the absence of leukocytes, while awaiting culture confirmation.