*Purpose: Proteinuria is common in kidney transplant recipients (KTRs), and is associated with an increased risk of graft failure. A rise in serum creatinine (SCr) is the most common indication for kidney graft biopsies. But there is limited information about biopsy findings and outcomes when the indication for biopsy is isolated proteinuria with stable Scr in KTRs.

*Methods: We analyzed all KTRs who underwent biopsy for isolated proteinuria with stable SCr between 01/2016 and 06/2020. Protocol biopsies and biopsy for other indications (research, guided by DSA etc) were excluded. Patients were divided into two groups based on the biopsy findings, Active Rejection (AR) and Other. We defined new proteinuria as urine protein to SCr ratio (UPC) > 0.5 gm/gm and worsening proteinuria as UPC doubled and more than 1. Risk factors for the AR and graft survival were outcomes of interest.

*Results: A total of 130 KTRs fulfilled our selection criteria;38 (29%) were in the AR group and 92 in the Other group. Most baseline characteristics were similar between the groups, including indication for biopsy as worsening or new proteinuria. The mean interval from transplant to biopsy in the AR group was 9.1±6. compared to 7.4±6.3 years (p=0.17) in the Other group. SCr, eGFR, and UPC at the time of biopsy were also similar between the groups. Not surprisingly, microvascular inflammation, tubulitis, and sum chronicity scores were higher in the AR group. In multivariate analysis (MV) model 1, only higher HLA mismatch (HR: 1.30; 95% CI: 1.06-1.59; p=0.01) was associated with AR and in model 2, male gender (HR: 0.45; 95% CI 0.23-0.89; p=0.02) was associated with a lower risk for AR. The degree of proteinuria was not associated with AR in either model. At last follow-up, 18% of grafts failed in the AR group (11% death censored), and 17% in the Other group (9% death censored) without significant difference. This was further confirmed by the K-M analysis.

*Conclusions: 29% of the patients were diagnosed with AR exclusively based on the proteinuria. Likely due to the early diagnosis without a significant rise in SCr, outcomes were similar in the rejection group compared to the Other group. Routine monitoring for proteinuria in KTRs followed by a biopsy for worsening or new proteinuria may help to identify early rejection.

« Back to 2021 American Transplant Congress