Background and purpose: Liquid biopsy is a kind of blood

urine and other non-solid biological tissue sampling analysis

mainly for malignant tumor diagnosis

monitoring and predicting its prognosis. In this research

we optimized the extraction of miRNA in urine

established a standardized means of liquid biopsy

screened and verified the miRNA markers in patients with bladder cancer. Methods: From Jan. 2014 to Sept. 2015

we used miRNA microarray in six patients with bladder cancer and six healthy controls. Samples of 78 cases of bladder cancer and 23 healthy controls were tested by real-time fluorescent quantitative polymerase chain reaction (RTFQ-PCR) to verify the relationship between miRNA markers in liquid biopsy and clinical pathological parameters. The diagnostic value of miRNA markers was also analyzed and compared. Results: We screened 10 miRNAs differential expression in urine. Combined with previous literature

we selected 20 miRNAs to verify their expression levels in bladder cancers and healthy controls. miR-509-5p/miR-124 ratio in the urine was found higher in patients with bladder cancer than in healthy controls (P0.000 1). With the rise of miR-509-5p/miR-124 ratio in urine

tumor stage and grade were also increased (P=0.003). When the cutoff was set at 0.41

the diagnostic sensitivity and specificity of miR-509-5p/miR-124 ratio were 73.1% and 82.6%

respectively. The AUC of miR-509-5p/miR-124 ratio to detect bladder cancer was 0.864

higher than that of urinary exfoliated cells (P=0.000 2). Conclusion: We optimized the extraction of miRNAs in urine

 established a standardized liquid biopsy of miRNA markers. The miR-509-5p/miR-124 ratio could be an ideal diagnostic marker for bladder cancer.