 Attaching barcodes to the ligated adapters prior to NGS during library preparation make absolute ddcfDNA quantification possible without the need for prior donor genotyping .This has been shown to provide additional clinical benefits if the absolute number of cfDNA copies is considered combined together with the fraction of ddcfDNA over cfDNA from the recipient to determine whether the allograft is being rejected or not.cfDNA allows a rapid, easy, non-invasive and repetitive method of sampling.