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Donor-derived cell-free DNA (dd-cfDNA) is proving its use as a marker of rejection in kidney transplantation. In October’s Clinical Chemistry, a team of researchers determined that absolute dd-cfDNA concentrations is a superior metric to fractional dd-cfDNA (a percentage metric) for surveying grafts in stable transplant patients over a prolonged period of time. “Absolute concentration is not affected by the decrease of total cell-free DNA; therefore is the preferred method,” senior author Michael Oellerich, MD, Hon MD, FAACC, FAMM, FFPath (RCPI), FRCPath, told CLN Stat.

Currently, dd-cfDNA’s main use is in clinical trials, although providers in the United States do use it and bill this service to Medicare. More than 50 studies have documented its clinical validity, with additional studies on the way, said Oellerich, a distinguished research professor of clinical chemistry with University Medical Center’s Goettingen’s Department of Clinical Pharmacology in Goettingen, Germany.

“Almost all published studies designed to establish clinically useful cut-off values to distinguish a healthy graft from one with injury have measured the dd-cfDNA (%) in the recipient’s plasma.

However, little is known about changes in host cfDNA, which represents the denominator in the percentage calculations, over time,” wrote Oellerich and colleagues.

In this prospective study, the investigators evaluated cfDNA dynamics in 303 clinically stable patients 1 to 5 years after they had kidney transplants, to see what variations in threshold values took place over time. They used droplet digital polymerase chain reaction to quantify the proportion of dd-cfDNA and concentrations of dd-cfDNA and total cfDNA in 929 plasma samples.

Dd-cfDNA fraction increased over time, due to a decrease in total cfDNA. In tandem with this finding, the investigators also observed increasing white-blood cell counts and decreasing tacrolimus concentrations. Compared with dd-cfDNA fraction, “the concentration of dd-cfDNA (cp/ml) was stable during the observation period, so that the threshold was not affected. The increase of dd-cfDNA fraction as opposed to absolute concentration can cause an increased number of false positive values,” summarized Oellerich. Based on these findings, absolute quantification emerges as the preferred method.

The investigators “call into question the singular focus on the proportion of dd-cfDNA as the relevant cfDNA readout of transplant health,” noted Iwijn De Vlaminck, PhD, in a related editorial.

But the study contained some limitations. “The authors examined only clinically stable transplant recipients and did not investigate the diagnostic performance of the relative versus absolute amount of dd-cfDNA,” according to De Vlaminck. He recommended that future studies compare dd-cfDNA metrics in all transplant settings that investigate cfDNA biomarkers, not just in kidney transplants.

“Diagnostic models that integrate the relative and absolute amount of dd-cfDNA also need to be considered,” added De Vlaminck.

Oellerich explored another angle to this topic in The Journal of Applied Laboratory Medicine. In this review, he and colleagues observed that dd-cfDNA could facilitate personalized immunosuppression, with the potential to reduce premature graft loss. Using a value proposition model, they evaluated dd-cfDNA’s potential benefits to stakeholders involved in organ transplantation, including doctors and adult organ transplant recipients, lab medicine and hospital management specialists, and insurers.

They determined that dd-cfDNA is a rapid, cost-effective, reproducible method to detect graft injuries, including rejection at an early actionable stage. It complements histology findings and helps exclude graft injuries, avoiding unnecessary biopsies. The method allows clinicians to detect under immunosuppression in patients at risk of de novo donor specific antibodies formation during immunosuppression minimization, said Oellerich. Overall, “the value proposition indicates that serial dd-cfDNA monitoring can facilitate personalized immunosuppression and thereby potentially decrease premature graft loss.”

On a broader scale, dd-cfDNA can shift emphasis from reaction to prevention, added Oellerich.