When is a urinalysis considered negative?

When is a Urinalysis Considered Negative

A urinalysis is considered negative for urinary tract infection when both leukocyte esterase AND nitrite tests are negative, which effectively rules out UTI in most clinical situations with an excellent negative predictive value of 90.5% and makes the likelihood of infection less than 0.3%. 1, 2

Key Components of a Negative Urinalysis

A truly negative urinalysis requires the absence of all the following markers:

• Negative leukocyte esterase - indicates absence of white blood cells/pyuria 1
• Negative nitrite - indicates absence of nitrate-reducing bacteria 1
• Microscopy showing <5-10 WBCs per high-power field - confirms absence of pyuria 1, 3
• No bacteria on microscopy - rules out significant bacteriuria 2

Diagnostic Performance of Negative Results

The combination of negative leukocyte esterase and negative nitrite achieves:

• Negative predictive value of 90.5% for ruling out UTI 1
• Sensitivity of 93% when either test is positive (meaning only 7% of true UTIs are missed when both are negative) 1, 2
• Effectively excludes UTI with <0.3% probability when both markers are absent 2

The absence of pyuria (negative leukocyte esterase AND no microscopic WBCs) has excellent negative predictive value for ruling out UTI across most patient populations. 1

Clinical Application Algorithm

When you encounter a negative urinalysis:

1. If the patient has NO urinary symptoms (no dysuria, frequency, urgency, fever, or gross hematuria) → Stop here, do not pursue further testing or treatment 1

2. If the patient HAS specific urinary symptoms but negative UA → Consider:

   • Non-urinary sources of symptoms in most cases 1
   • Repeat specimen collection if contamination suspected (high epithelial cells) 1
   • Proceed to culture only if suspected pyelonephritis/urosepsis with systemic signs (fever >38.3°C, hypotension, rigors) 1

3. Special populations requiring culture despite negative UA:

   • Febrile infants <2 years - culture is mandatory as 20% of pyelonephritis cases lack pyuria initially 3, 2
   • Suspected pyelonephritis or urosepsis with systemic signs 1

Critical Pitfalls to Avoid

• Do NOT rule out UTI based on negative nitrite alone - nitrites have only 19-48% sensitivity, so a negative result means little 1, 3
• Do NOT ignore clinical context - the negative predictive value applies to properly collected, fresh specimens processed within 1-2 hours 1, 2
• Do NOT test asymptomatic patients - even if the UA were positive, asymptomatic bacteriuria should not be treated in most populations 1
• Do NOT accept bag-collected specimens as definitive in children - these have only 15% positive predictive value and require catheterized confirmation if positive 1, 2

Specimen Quality Considerations

A negative urinalysis is only reliable when:

• Properly collected - midstream clean-catch in cooperative adults, catheterization in women unable to provide clean specimens, catheterization or suprapubic aspiration in infants 1, 2
• Processed promptly - within 1 hour at room temperature or 4 hours if refrigerated 1, 2
• Low epithelial cell count - high epithelial cells suggest contamination and may require repeat collection 1

When Negative UA Still Requires Further Workup

Despite a negative urinalysis, proceed with urine culture in these specific scenarios:

• Febrile infants and children <2 years with suspected UTI (pyuria absent in 20% of culture-proven pyelonephritis) 3, 2
• Suspected pyelonephritis with fever, flank pain, and systemic symptoms 1
• Suspected urosepsis with hemodynamic instability 1
• Recent catheter obstruction with fever 1