Predictive value of urinary interleukin-6 for symptomatic urinary tract infections in a nursing home population

To study urinary interleukin-6, interleukin-8 and pyuria during episodes of asymptomatic bacteriuria and symptomatic urinary tract infection in the institutionalized elderly, and to investigate the role of interleukin-6 as a biomarker for differential diagnosis.

Levels of interleukin-6, interleukin-8 and pyuria were assessed in 35 older adults with asymptomatic bacteriuria and symptomatic urinary tract infection to define possible diagnostic thresholds. In a two-phase intervention study, the antibiotic treatment for urinary tract infection before and after introduction of urinary interleukin-6 as a biomarker was then assessed.

Asymptomatic bacteriuria patients had no or low levels of interleukin-6, and low levels of interleukin-8 and pyuria. Women had lower interleukin-6 and interleukin-8 than men (P = 0.05). Interleukin-6 was the only marker showing significant increases during urinary tract infection episodes in patients with both asymptomatic bacteriuria and urinary tract infection, in pooled (P = 0.042) and in paired intra-individual (P = 0.017) comparisons. In the intervention study lectures, the increased use of urine cultures and the introduction of interleukin-6 as a biomarker reduced antibiotic treatments by 20%. Antibiotic-treated urinary tract infection episodes had increased interleukin-6 as compared with urinary tract infection episodes not treated (P = 0.02), and as compared with asymptomatic bacteriuria patients (P < 0.0001). The sensitivity and specificity of interleukin-6 (cut-off 25 pg/mL) differentiating asymptomatic bacteriuria from urinary tract infection was 57% and 80%, respectively.

Urinary interleukin-6 shows promise as a biomarker to detect the transition from asymptomatic bacteriuria to symptomatic urinary tract infection in older adults. Further larger studies with robust methodology are warranted to determine whether development for near to patient testing would be worthwhile.