From the Guidelines
The diagnostic criteria for a urinary tract infection (UTI) based on urinalysis (UA) should prioritize clinical symptoms over UA findings, as the diagnostic value of UA for UTI is limited 1. When considering UA results, the presence of pyuria, bacteriuria, positive leukocyte esterase, and positive nitrites can be indicative of a UTI.
- A UTI is strongly suggested when both leukocyte esterase and nitrites are positive, with a high specificity of 96% if both tests are positive 1.
- Pyuria alone is sensitive but not specific for UTI, as it can occur in other conditions.
- Bacteriuria on microscopy correlates well with positive cultures (>100,000 colony-forming units/mL).
- Hematuria may be present but is less specific. The gold standard for diagnosis remains urine culture, but UA provides rapid results to guide initial treatment decisions.
- In symptomatic patients with dysuria, frequency, and urgency, even a partially positive UA may warrant empiric treatment while awaiting culture results 1.
- The absence of all UA abnormalities makes UTI unlikely but doesn't completely rule it out, especially in patients with dilute urine, recent antibiotic use, or infection with non-nitrite-producing organisms. Urine cultures are reasonable for complicated cases and/or recurrent UTIs, particularly in suspected pyelonephritis, to guide targeted therapy 1.
- In simple uncomplicated cystitis in healthy nonpregnant patients, routine cultures are not necessary 1.
From the Research
Diagnostic Criteria for Urinary Tract Infection (UTI) based on Urinalysis (UA)
The diagnostic criteria for UTI based on UA include:
- The presence of leukocytes (white blood cells) in the urine, which indicates an infection 2, 3, 4
- The presence of nitrite in the urine, which indicates the presence of bacteria 2, 5, 3
- The presence of pyuria (pus in the urine), which is a sign of infection 3, 4
- The presence of leukocyte esterase, which is an enzyme produced by white blood cells 5, 4, 6
Sensitivity and Specificity of Urinalysis Tests
The sensitivity and specificity of urinalysis tests for UTI are:
- Leukocyte esterase test: sensitivity 63.6% and specificity 44.2% 4
- Nitrite test: sensitivity 20.6% and specificity 93.5% 2
- Combined leukocyte esterase and nitrite test: sensitivity 66.7% and specificity not reported 4
- Pyuria: sensitivity 95.6% and specificity 60.9% 4
Urinalysis Parameters for Predicting UTI
The urinalysis parameters that can be used to predict UTI include: