Date Published: April 16, 2019
Publisher: Public Library of Science
Author(s): Malou L. H. Snijders, Dennis A. Hesselink, Marian C. Clahsen-van Groningen, Joke I. Roodnat, Stanislaw Stepkowski.
Calcium oxalate (CaOx) deposition in the kidney may lead to loss of native renal function but little is known about the prevalence and role of CaOx deposition in transplanted kidneys.
In patients transplanted in 2014 and 2015, all for-cause renal allograft biopsies obtained within 3 months post-transplantation were retrospectively investigated for CaOx deposition. Additionally, all preimplantation renal biopsies obtained in 2000 and 2001 were studied.
In 2014 and 2015, 388 patients were transplanted, of whom 149 had at least one for-cause renal biopsy. Twenty-six (17%) patients had CaOx deposition. In the population with CaOx deposition: Patients had significantly more often been treated with dialysis before transplantation (89 vs. 64%; p = 0.011); delayed graft function occurred more frequently (42 vs. 23%; p = 0.038); and the eGFR at the time of first biopsy was significantly worse (21 vs. 29 ml/min/1.73m2; p = 0.037). In a multivariate logistic regression analysis, eGFR at the time of first biopsy (OR 0.958, 95%-Cl: 0.924–0.993, p = 0.019), dialysis before transplantation (OR 4.868, 95%-Cl: 1.128–21.003, p = 0.034) and the time of first biopsy after transplantation (OR 1.037, 95%-Cl: 1.013–1.062, p = 0.002) were independently associated with CaOx deposition. Graft survival censored for death was significantly worse in patients with CaOx deposition (p = 0.018). In only 1 of 106 preimplantation biopsies CaOx deposition was found (0.94%).
CaOx deposition appears to be primarily recipient-derived and is frequently observed in for-cause renal allograft biopsies obtained within 3 months post-transplantation. It is associated with inferior renal function at the time of biopsy and worse graft survival.
Oxalic acid is a small decarboxylate ion (C2O4) and is the end-product of many metabolic pathways. Oxalic acid is eliminated through free glomerular filtration and secretion by the proximal tubule . The plasma concentration of oxalic acid is determined by the balance between dietary intake, intestinal absorption, endogenous production and renal excretion . Normal plasma concentrations are below 5 μmol/l [3–4].
This study demonstrates that CaOx deposition is present in as many as 17% of the patients with a for-cause renal allograft biopsy within the first 3 months after transplantation and that these deposits are primarily recipient-derived. DGF was more common in patients with CaOx in their biopsies. In addition, the presence of CaOx was associated with a significantly lower eGFR at the time of biopsy in both univariate and multivariate analysis. As there was no significant difference in best eGFR before biopsy, this indicates that patients with CaOx deposition had a greater loss of renal function prior to biopsy.