Introduction: Delayed graft function (DGF) after kidney transplantation occurs in about 12-26% of pediatric kidney transplants. Urine neutrophil gelatinase-associated lipocalin (uNGAL) has been studied in small cohorts and has shown that an elevated uNGAL post-transplant level is associated with the development of DGF. However, there have been no prospective studies in pediatric patients looking at uNGAL trends immediately post kidney transplantation.
Case Summary: Patient A is a highly sensitized 22-year-old with end-stage kidney disease (ESKD) from reflux nephropathy with neurogenic bladder s/p augmentation who underwent deceased donor (donation after cardiac death) kidney transplantation and right native nephrectomy.  Pre-transplant serum creatinine (sCr) was 2.8mg/dL. Day one post-transplant, uNGAL was 2399 ng/mL and sCr was 2.7 (Figure 1). On post-transplant day 2, uNGAL decreased to 2004 ng/mL but sCr increased to 3mg/dL. Urine output during this time was noted to be equivocal to pre-transplant daily volume. Post-transplant day 4 is when uNGAL decreased significantly to 545ng/mL, an approximate 75% decrease. SCr remained elevated on post-transplant day 7 at 3.4 ng/mL. Biopsy was performed that showed acute tubular injury and mild glomerulitis and peritubular capillaritis in the setting of concern for de novo donor specific antibodies. They were treated with rituximab and intravenous immunoglobulin. Serum creatinine did not decrease to below pre-transplant levels until post-operative day 14 – approximately 9 days after uNGAL had dropped to less than 500 ng/mL.

Patient B is a 15-year-old with ESKD of unknown etiology on peritoneal dialysis who underwent a living unrelated kidney transplant. Baseline sCr was 13.4 mg/dL. Immediately post-transplant while in the intensive care unit, ultrasound noted no arterial flow to the kidney resulting in return to the operating room. Perfusion was re-established and the allograft was reimplanted; however, with minimal urine output in the first 24 hours. UNGAL on post-transplant day 1 was elevated at 1717 ng/ml and creatinine remained 12.7 mg/dL (Figure 2). UNGAL increased on post-transplant day 2 to a maximum of 4038 ng/mL. They received hemodialysis on the same day with subsequent treatments as per Figure 2. UNGAL showed more than 50% reduction to 1554 ng/mL on post-operative day 6. Urine output did not significantly increase until day 8 post-transplant and sCr did not significantly decrease until day 16 post-transplant. In this patient, uNGAL decreased 2 days before urine output increased and 10 days before a significant decline in sCr.

Conclusions: In these patients, uNGAL decreased 9-10 days prior to serum creatinine and 2 days prior to an increase in urine output in Patient B. Urine NGAL may be an earlier marker of resolution of DGF. Further studies are warranted to determine the exact clinical utility in the use of uNGAL and the course of delayed graft function.