Does the presence of trace blood and trace leukocytes (white blood cells) indicate a urinary tract infection (UTI)?

From the Guidelines

The presence of trace blood and trace leukocytes on a urinalysis does not necessarily indicate a urinary tract infection (UTI), and a definitive diagnosis typically requires significant leukocytes along with bacteria in the urine and accompanying symptoms. While these findings can suggest inflammation in the urinary tract, trace amounts can occur due to many factors including dehydration, vigorous exercise, contamination during collection, menstruation in women, kidney stones, or other urinary tract inflammation 1. According to a Class II meta-analysis of diagnostic tests for urinary tract infection, the sensitivity and specificity of leukocyte esterase or nitrite were 88% and 79%, respectively, and urine WBC counts (>10/mL) had a sensitivity and specificity of 74% and 86%, respectively 1.

Key Considerations

• A urine culture is necessary to confirm the presence of a UTI, as rapid diagnostic tests "cannot replace urine culture" 1.
• The presence of nitrite or leukocyte esterase on a urine dipstick has a sensitivity of 88% and a false positive rate of 7% for urinary tract infection 1.
• If symptoms are present along with trace findings, a healthcare provider might recommend a urine culture to confirm infection before prescribing antibiotics.
• Without symptoms, trace findings often don't require treatment, and increasing fluid intake and following up with a healthcare provider is recommended, especially if symptoms like pain with urination, increased frequency, fever, or visible blood in urine develop.

Diagnostic Approach

• Urinalysis can be performed on any specimen, including one collected from a bag applied to the perineum, but the specimen must be fresh to ensure sensitivity and specificity of the urinalysis 1.
• A negative urinalysis result from a bagged specimen may be useful for clinical decision-making, but a positive bagged urinalysis result should prompt a urine culture obtained by catheterization or suprapubic aspiration 1.

From the Research

Presence of Trace Blood and Leukocytes in Urinary Tract Infections

• The presence of trace blood and trace leukocytes (white blood cells) in urine can be an indicator of a urinary tract infection (UTI) 2, 3, 4, 5, 6.
• Studies have shown that the detection of leukocytes in urine is a reliable method for diagnosing UTIs, with sensitivity and specificity values ranging from 63.6% to 95.6% 3, 4.
• The presence of pyuria (leukocytes in urine) has been found to have a higher sensitivity and specificity for detecting UTIs compared to dipstick tests 4.
• Flow cytometry has been shown to be a rapid and reliable method for detecting UTIs, with high sensitivity and specificity values 3, 5.
• The combination of leukocyte esterase and nitrite tests has been found to be more useful than single tests for detecting UTIs 4.

Diagnostic Value of Leukocytes and Bacteria in UTIs

• The diagnostic value of leukocytes and bacteria in UTIs has been evaluated in several studies, with results showing strong agreement between urine flow cytometry and microscopic examination 3.
• The use of cutoff values for bacterial and leukocyte parameters in urine flow cytometry has been found to demonstrate good performance in detecting acquired symptomatic UTIs 3.
• The presence of leukocyturia (leukocytes in urine) in the absence of significant bacteriuria mandates further diagnostic evaluation 6.

Laboratory Diagnosis of UTIs

• Laboratory diagnosis of UTIs is typically based on the presence of clinical symptoms, nitrite strip test results, and semi-quantitative measurement of white blood cells in urine 2.
• Urine culture is considered the gold standard for diagnosing UTIs, but it is time-consuming and costly 2.
• Novel biomarkers, such as leukocyte esterase, C-reactive protein, and procalcitonin, have been identified as potential diagnostic markers for UTIs 2.