Neutrophil infiltration of kidney grafts: incidence, associated factors and graft survival.

BACKGROUND: Neutrophil tubulointerstitial infiltration (NTI) of kidney grafts is commonly attributed to urinary tract infection ('ascending nephritis'). Without clinical evidence of urinary tract infection, it is an unexplained finding and was therefore explored in this retrospective study.

METHODS: NTI after kidney transplantation was examined in 1753 recipients with 6749 biopsies, including protocol biopsies (59.1%) to determine the unbiased natural prevalence of NTI. We determined associated factors for NTI by logistic regression and graft outcomes with NTI by Kaplan-Meier survival analyses.

RESULTS: NTI was diagnosed in 178 patients (10.2%), with 131 patients in the first transplant year and in 47 thereafter. Twenty-six patients (14.6%) had repeated findings of NTI, and 65 patients (36.5%) diffuse patterns of NTI. NTI was associated with inferior death-censored graft survival during long-term follow-up up to 21 years, especially with repeated and diffuse findings in the first transplant year. Common associated factors for NTI within and beyond the first year were urinary tract infections (22%) and female donor organs. Additionally, NTI during the first transplant year was associated with delayed graft function (1.5%), acute tubular injury (18.8%) and rejection (47.0%). After the first transplant year, female recipients, especially those of younger age, had NTI 2-fold more frequently, mainly coincident with urinary tract infection.

CONCLUSION: Diagnosis of NTI should prompt the search for urinary tract infection and rejection. The association of NTI with rejection encourages further study on neutrophils in kidney graft rejection. The predisposition of female donor organs to NTI is a new observation and should be explored further.