Urinary Exosomal microRNA-21 as a Marker for Scrub Typhus-Associated Acute Kidney Injury

Background: Urinary microRNA (miRNA)-21 is a biomarker for acute kidney injury (AKI). We conducted this study to determine if a urinary exosomal analysis for this biomarker could serve as a novel diagnostic approach for detecting kidney disease. Materials and Methods: We investigated the clinical significance of urinary exosomal miRNA-21 levels for AKI in scrub typhus patients. We collected 138 urine samples from scrub typhus patients at the time of admission. Urinary exosomal miRNA-21 was assessed in 25 age- and sex-matched scrub typhus patients with and without AKI. Results: The total leukocyte count was higher in AKI patients than in non-AKI patients (10.40 x 10(3)/mL vs. 6.40 x 10(3)/mL, p < 0.01). Urinary exosomal miRNA-21 levels were higher in the AKI group than in the non-AKI group (20.1 +/- 1.2 vs. 17.8 +/- 1.8 Delta Ct value of miRNA-21, p < 0.01). Additionally, the miRNA-21 levels correlated directly with the total leukocyte counts and inversely with the estimated glomerular filtration rate. A receiver operating characteristic curve analysis demonstrated good discriminative power for the diagnosis of scrub typhus-associated AKI, with an area under the curve value of 0.907. Conclusion: Urinary exosomal miRNA-21 could be a surrogate marker for scrub typhus-associated AKI diagnosis.