Intra-individual variation of miRNA expression levels in human plasma samples

Background: Circulating miRNAs as potential non-invasive biomarkers for disease risk assessment and cancer early diagnosis have attracted increasing interest. Little information, however, is available regarding the intra-individual variation of circulating miRNA levels.Methods: We measured expression levels of a panel of 800 miRNAs in repeated plasma samples from 51 healthy individuals that were collected 6 to 12months apart and evaluated the intra-individual variation by the intra-class correlation coefficient (ICC).Results: After background correction, a total of 185 miRNAs were detected in at least 10% of the plasma samples, with 69 and 28 miRNAs being detected in 50% and 90% of samples, respectively. The median ICC was 0.46 for these 185 miRNAs. Among them, 41% (75 miRNAs) had an ICC0.5, and 23% (42 miRNAs) had an ICC0.6. The ICC is higher for miRNAs with higher expression levels or higher detection rates, when compared to those with lower expression levels or lower detection rates.Conclusions: These results suggest that common circulating miRNAs are stable over a relatively long period and can serve as reliable biomarkers for epidemiological and clinical research.