Technical Aspects Related to the Analysis of Circulating microRNAs

Specific and sensitive noninvasive biofluid-based biomarkers are always needed in the laboratory diagnosis of diseases. Biomarkers are applied not only for diagnostic purposes but for stratifying a disease and for assessing the therapy response or disease progression. MicroRNAs (miRNAs) are short noncoding RNA molecules regulating gene expression posttranscriptionally. They are frequently dysregulated in many physiological and pathophysiological conditions. miRNAs are present in the circulation and in other biofluids that are common matrices for clinical laboratory testing that has raised the possibility that miRNAs may serve as novel biomarkers. Their excellent stability also supports the possibility that miRNAs once will be routinely used biomarkers in clinical practice. From an analytical point of view, there are many factors (starting material, sample storage and processing, different RNA extraction and detection methods, intra- and interassay variability, and assay interferences) to consider if a miRNA as biomarker is aimed to be introduced as a clinical laboratory test. Despite several pre-analytical and analytical factors that still need standardization, a significant number of studies have been published about the potential role of circulating miRNAs as biomarkers. Due to the lack of standardization of methods, there are a lot of discrepancies among results. In this chapter, we aimed to summarize the current findings about circulating miRNAs focusing on the analytical points related to miRNAs measurements from biofluids.