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Background: Macrophages are involved in kidney transplants. The aim of the study was to investigate if changes exist in the levels of glomerular macrophage index (GMI) between two consecutive kidney transplant biopsies, and if so to determine their potential impact on graft survival.

Methods: Two consecutive biopsies were performed on the same renal graft in 623 patients. GMI was categorized into three GMI classes: ≤1.8 Low, 1.9–4.5 Medium, and ≥4.6 High. This division yielded nine possible switches between the first and second biopsies (Low-Low, Low-Medium, etc.). Cox-regressions were used and hazard ratios (HR) with 95% confidence interval (CI) are presented.

Results: The worst graft survival was observed in the High-High group, and the best graft survival was observed in the Low-Low and High-Low groups. Compared to the High-High group, a reduction of risk was observed in nearly all other decreasing groups (reductions between 65% and 80% of graft loss). After adjustment for covariates, the risk for graft-loss was lower in the Low-Low (HR = 0.24, CI 0.13–0.46), Low-Medium (HR = 0.25, CI 0.11–0.55), Medium-Low (HR = 0.29, CI 0.11–0.77), and the High-Low GMI (HR = 0.31, CI 0.10–0.98) groups compared to the High-High group as the reference.

Conclusions: GMI may change dynamically, and the latest finding is of most prognostic importance. GMI should be considered in all evaluations of biopsy findings since high or increasing GMI levels are associated with shorter graft survival. Future studies need to consider therapeutic strategies to lower or maintain a low GMI. A high GMI besides a vague histological finding should be considered as a warning sign requiring more frequent clinical follow up.