What does a high White Blood Cell (WBC) count with no visible leukocytes in a urine analysis indicate?

From the Guidelines

A high white blood cell (WBC) count in a urinalysis with no visible leukocytes typically indicates pyuria with lysis of the white blood cells, suggesting a urinary tract infection (UTI). This finding is supported by the study published in the Annals of emergency medicine 1, which discusses the use of rapid diagnostic tests of the urine to help guide decisions regarding the need for urine cultures or empiric treatment pending culture results. The presence of leukocyte esterase, as indicated by a high WBC count, has higher sensitivity but lower specificity for UTI compared to the nitrite test. Key points to consider in this scenario include:

• The leukocyte esterase test has a sensitivity of 88% and a false positive rate of 7% for UTI 1.
• If the results of both nitrite and leukocyte esterase tests are positive, the specificity is 96%, indicating a high likelihood of UTI 1.
• The absence of visible leukocytes may be due to lysis of WBCs, which can occur within 1-2 hours at room temperature, in dilute or alkaline urine, or as a result of early antibiotic treatment. Considering these factors, treatment with antibiotic therapy should be considered if clinical symptoms of UTI are present, typically with nitrofurantoin 100mg twice daily for 5 days or trimethoprim-sulfamethoxazole twice daily for 3 days for uncomplicated cases. A urine culture should be obtained before starting antibiotics to identify the causative organism and confirm appropriate treatment.

From the Research

Urine Analysis Results

• A high White Blood Cell (WBC) count with no visible leukocytes in a urine analysis can be an indication of several factors, including the method of analysis used and the presence of certain medical conditions.
• According to a study published in 1976 2, the absence of pyuria (visible leukocytes) provides strong evidence against the presence of urinary tract infection, suggesting that a high WBC count without visible leukocytes may not necessarily indicate an infection.

Diagnostic Accuracy of Urinalysis

• A study from 2009 3 found that the presence of pyuria (>5 WBC/HPF) had a sensitivity of 82-89% and specificity of 53-55% in detecting urinary tract infections in hemodialysis patients, highlighting the limitations of urinalysis in certain populations.
• Another study from 2024 4 investigated the optimal urine WBC threshold in pediatric urinary tract infection and found that a threshold of 100/μL had a sensitivity of 82.2% and negative predictive value of 86.2%, but also resulted in a significant number of missed UTIs.

Interpretation of Urine Analysis Results

• A study published in 2001 5 noted that the method of analysis affects the interpretation of urinalysis results, with a hemocytometer yielding a value of > or = 10 WBC/mm3 significant for bacteriuria, while manual microscopy studies show > or = 8 WBC/high-power field reliably predicts a positive urine culture.
• A study from 2003 6 found that individuals with spinal cord injuries were frequently not accurate at predicting whether they had a UTI based on their symptoms, highlighting the importance of laboratory tests like urinalysis in diagnosing UTIs.

Possible Explanations

• The presence of a high WBC count without visible leukocytes may be due to the presence of certain medical conditions, such as inflammation or infection, that do not cause visible pyuria.
• The use of automated urinalysis may provide more sensitive detection of leukocytes and bacteria in the urine, but may also lead to false positives or false negatives 5.
• The accuracy of urinalysis results can be affected by various factors, including the method of analysis, the population being tested, and the presence of certain medical conditions 3, 4, 6.