Size and Concentration of Cell-Free DNA Measured Directly from Blood Plasma, without Prior DNA Extraction

Cell-free DNA in human blood plasma(cfDNA) is now widely usedand studied as a biomarker for several physiological and pathologicalsituations. In addition to genetic and epigenetic alterations thatprovide information about the presence and the nature of non-constitutiveDNA in the body, cfDNA concentration and size distribution may potentiallybe independent biomarkers suitable for monitoring at-risk patientsand therapy efficacy. Here, we describe a simple, in-line, method,which measures cfDNA concentration and size distribution from onlya few microliters of plasma without the need to extract and/or concentratethe DNA prior to the analysis. This method is based on a dual hydrodynamicand electrokinetic actuation, adapted for samples containing saltsand proteins such as biological fluids. The method provides analyticalperformances equivalent to those obtained after purification and concentrationof cfDNA, with a precision of similar to 1% for size features and of10-20% for the concentrations of the different size fractions.We show that concentration and size distribution of cfDNA analyzedfrom plasma can differentiate advanced lung cancer patients from healthycontrols. This simple and cost-effective method should facilitatefurther investigations into the potential clinical usefulness of cfDNAsize profiling.