Transplanted organs release cell-free DNA into the bloodstream of the recipient. This graft-derived cell-free DNA (GcfDNA) is a sensitive biomarker for organ health, since higher GcfDNA levels are indicative of increased cell-death in the graft. This protocol describes a method to measure relative GcfDNA concentrations by ddPCR assays. The method uses a set of preselected SNP assays from which the informative SNPs for each recipient-donor combination are selected in a straightforward two-step procedure that requires only one blood draw. Sampling of donor tissue and separate genotyping is not required, rendering the technique applicable also to patients, whose transplantation was not recent. In these patients there will be mostly no access to donor DNA anymore.
Keywords: Rejection monitoring; Transplantation.