Supplementary Material for: Urinary Post-Translationally Modified Fetuin-A Protein is Associated with Increased Risk of Graft Failure in Kidney Transplant Recipients

Introduction: Urinary fetuin-A has been identified as a biomarker for acute kidney injury and is proposed as a biomarker for early detection of kidney function decline. We investigated whether fetuin-A could serve as a marker of graft failure in kidney transplant recipients (KTR). Methods: Data of KTR with a functioning graft ≥ 1 year that were enrolled in the TransplantLines Food and Nutrition Biobank and Cohort study were used. Graft failure was defined as the need of re-transplantation or (re-)initiation of dialysis). Urinary Fetuin-A was measured using an enzyme-linked immunosorbent assay kit that detected post-translationally modified fetuin-A in the urine (uPTM-FetA). In the main analyses, 24h uPTM-FetA excretion was used. In the sensitivity analyses, we excluded the outliers in 24h uPTM-FetA excretion, and we used uPTM-FetA concentration and uPTM-FetA concentration indexed for creatinine instead of 24h uPTM-FetA excretion. Results: A total of 627 KTR (age 53 ± 13 years, 42% females) were included at 5.3 [1.9-12.2] years after transplantation. Estimated glomerular filtration rate (eGFR) was 52 ± 20 mL/min/1.73 m2 and uPTM-FetA excretion was 34 [17-74] µg/24h. During a median follow-up of 5.3 [4.5-6.0] years after baseline measurements, 73 (12%) KTR developed graft failure. The association of 24h uPTM-FetA excretion with increased risk of graft failure was not constant over time, with increased risk only observed after 3 years from baseline measurements, independent of potential confounders including kidney function and 24h urinary protein excretion (hazard ratio per doubling of 24h uPTM-FetA excretion = 1.31; 95% confidence interval = 1.06-1.61). This finding was robust in the sensitivity analyses. Conclusions: Our findings suggest that uPTM-FetA can be used as a marker for early detection of graft failure in KTR. Further studies are needed to confirm our findings.