Washington--Results from a small study demonstrate that urinary interleukin-8 (IL-8) can be used as an early diagnostic tool for nosocomial urinary tract infections, Mexican infectious disease specialists said during a presentation at the 45th Interscience Conference on Antimicrobial Agents and Chemotherapy here. IL-8 appears to offer a faster alternative to quantitative cultures, according to the researchers.
"Our study suggests that the urinary IL-8 levels rise earlier than the presence of leukocytes in the urine or bacterial growth on culture plates, often within 2 hours of testing compared to 2 days for culture," said Jose Flores Figueroa, MD, a fellow in infectious disease, Hospital Central Norte de PEMEX, Mexico City. "In addition, the IL-8 test has high sensitivity and specificity values for UTI."
IL-8 vs. culture
A study, therefore, was carried out by Dr. Flores Figueroa and colleagues to determine the time of elevation of urinary IL-8 compared with quantitative cultures for the diagnosis of nosocomial UTI in urinary catheterized patients.
Sixteen hospitalized newly urinary catheterized patients were followed. Urinary quantitative cultures and measurement of urinary IL-8 were carried out immediately at the moment of urinary catheterization and every 24 hours thereafter up to the development of a UTI, defined as a leukocyte count >5 × 108/L or a pure or mixed culture of bacteria with >103 colony forming units (CF)/mL. The amounts of IL-8 were measured by enzyme-linked immunosorbent assay (ELISA), according to the instructions of the test's manufacturer (Pierce Endogen, Rockford, IL), performed on a microtiter plate with a monoclonal antibody directed against the corresponding cytokine. Differences at three time points were estimated by the Wilcoxon signed-rank test: the time for growth on quantitative culture, rise of urinary leukocytes, and elevation of urinary IL-8.
In 12 of 16 patients (86%), the urine culture yielded Escherichia coli. Candida albicans was reported in two patients (14%), Proteus mirabilis in one patient, and Pseudomonas aeruginosa in one patient.
Median IL-8 concentrations at the time of catheterization were 10 pg/mL (range, 0-23 pg/mL), compared with 2,340 pg/mL (range, 46-15,809 pg/mL) at the moment of UTI (p<.0001). Urinary IL-8 values were elevated in two patients from the first sample on day 0 and in 14 of 16 patients at the moment of UTI. The first sample at day 0, which in all patients was culture-and leukocyte-negative, was used as the non-UTI control. The peak of urinary IL-8 at different time points was used for calculating the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (LR+) and negative likelihood ratio (LR–).