The association of calcium oxalate deposition in kidney allografts with graft and patient survival

Abstract

Background: Whether calcium oxalate (CaOx) deposition in kidney allografts following transplantation (Tx) adversely affects patient outcomes is uncertain, as are its associated risk factors.

Methods: We performed a retrospective cohort study of patients who had kidney allograft biopsies performed within 3 months of Tx at Brigham and Women's Hospital and examined the association of CaOx deposition with the composite outcome of death or graft failure within 5 years.

Results: Biopsies from 67 of 346 patients (19.4%) had CaOx deposition. In a multivariable logistic regression model, higher serum creatinine [odds ratio (OR) = 1.28 per mg/dL, 95% confidence interval (CI) 1.15-1.43], longer time on dialysis (OR = 1.11 per additional year, 95% CI 1.01-1.23) and diabetes (OR = 2.26, 95% CI 1.09-4.66) were found to be independently associated with CaOx deposition. CaOx deposition was strongly associated with delayed graft function (DGF; OR = 11.31, 95% CI 5.97-21.40), and with increased hazard of the composite outcome after adjusting for black recipient race, donor type, time on dialysis before Tx, diabetes and borderline or acute rejection (hazard ratio 1.90, 95% CI 1.13-3.20).

Conclusions: CaOx deposition is common in allografts with poor function and portends worse outcomes up to 5 years after Tx. The extent to which CaOx deposition may contribute to versus result from DGF, however, cannot be determined based on our retrospective and observational data. Future studies should examine whether reducing plasma and urine oxalate prevents CaOx deposition in the newly transplanted kidney and whether this has an effect on clinical outcomes.

Keywords: biopsy; calcium oxalate; graft survival; kidney transplantation; renal insufficiency.

FIGURE 1

CaOx deposition in a kidney allograft with delayed graft function at 20 days post-transplant. Left panel: this hematoxylin and eosin-stained section of kidney cortex reveals preserved kidney parenchyma with moderate distention of all tubules. Several tubules contain transparent crystals best visualized when the sections are examined under polarized light (right panel). Oxalate crystals are dissolved and disappear under the staining conditions of routinely used special stains, including PAS, Masson’s trichrome and Jones’ silver methenamine stains. (H&E; final magnification: 58×, bar = 250 µm).

FIGURE 2

Time to death or graft failure after kidney Tx among recipients with versus without CaOx deposition on early allograft biopsies.