Triggered Urine Interleukin-6 Correlates to Severity of Symptoms in Nonfebrile Lower Urinary Tract Infections

Purpose: Objective diagnosis of symptomatic urinary tract infections in patients prone to asymptomatic bacteriuria is compromised by local host responses that are already present and the positive urine culture. We investigated interleukin-6 as a biomarker for nonfebrile urinary tract infection severity and diagnostic thresholds for interleukin-6 and 8, and neutrophils to differentiate between asymptomatic bacteriuria and urinary tract infection. Materials and Methods: Patients with residual urine and neurogenic bladders due to spinal lesions included in a long-term Escherichia coli 83972 asymptomatic bacteriuria inoculation trial were monitored for 2 years. Symptom scoring and urine sampling to estimate interleukin-6 and 8, and neutrophils were performed regularly monthly and at urinary tract infection episodes. Results: Patients were followed in the complete study for a mean of 19 months (range 10 to 27) and those with asymptomatic bacteriuria with E. coli 83972 were followed a mean of 11 months (range 4 to 19). A total of 37 nonfebrile urinary tract infection episodes with complete data on interleukin-6 and 8, neutrophils and symptom scoring were documented. Interleukin-6 was the only marker that persistently increased during urinary tract infection compared to asymptomatic bacteriuria in pooled and paired intra-individual comparisons (p < 0.05). Interleukin-6 above the threshold (greater than 25 ng/l) correlated to more severe urinary tract infection symptoms (p < 0.05). The sensitivity and specificity of all biomarkers were poor/moderate when differentiating asymptomatic bacteriuria vs all urinary tract infection episodes. However, in urinary tract infections with worse symptoms interleukin-6 and neutrophils demonstrated equal good/excellent outcomes. Conclusions: Triggered interleukin-6 correlated to urinary tract infection symptom severity and demonstrated a promising differential diagnostic capacity to discriminate urinary tract infection from asymptomatic bacteriuria. Future studies should explore interleukin-6 as a biomarker of urinary tract infection severity and assess the treatment indication in nonfebrile urinary tract infections.