Calcium Oxalate Microdeposition in Failing Kidney Grafts L. Memeo, I. Pecorella, A. Ciardi, G. Salvati, I. De Nuccio, U. Di Tondo, and R. Cortesini R ECENT studies have shown that renal cell injury and death are central to the process of urolithiasis. 1,2 The development of acute or chronic renal failure in kidney transplanted patients is usually associated with diffuse epi- thelial tubular cell damage. The present study was per- formed to evaluate the actual incidence of microscopical calcium oxalate deposition in failed renal allografts. MATERIALS AND METHODS Forty allograft nephrectomies (28 males and 12 females, mean age of 33.2 years), performed between 1986 and 1999, were selected. Twenty patients had been grafted from cadaveric donors; of the remaining cases, 15 had received a kidney from a living related donor. Except for six patients who received steroid-azathioprine immunosuppression, all recipients were treated with cyclosporine A and low doses of steroids. None had primary or acquired hyperoxaluria as the cause of original end-stage renal disease, and none had a history of kidney stones or urinary infection. Kidney failure occurred after a time period ranging from 2 days to 11 years posttransplant and was secondary to acute rejection in 17 cases, chronic rejection in 15, ischemic necrosis in five, acute or chronic pielonephritis in two, and allergic microangiopathy in one. No blood chemistry evaluations for oxalemia were performed. Clinical data are summarized in Table 1. Multiple sections cut from formalin-fixed, paraffin-embedded blocks and stained with haematoxylin-eosin (H&E) were examined using partially crossed polarizing screens. The presence of calcium oxalate crystals in different segments of the nephron or in the interstitium was recorded. Birefringent deposits with characteristic green iridescence, presenting as large plate-like or diamond- shaped crystals, or any shape, provided that the crystals displaced tissue structures, were studied. Confirmation of the crystal nature was obtained using Yasue’s method, a histochemical stain consid- ered to be specific for calcium oxalate, 3 while usual stains for calcium (alizarin red and von Kossa’s method) were negative. Silver nitrate–rubeanic acid with 5% acetic acid pretreatment (Yasue’s method) stains only calcium oxalate, since calcium phosphate and calcium carbonate are dissolved with the acetic acid. 3 A thyroid with multiple deposits of calcium oxalate and hydroxyapatite crystals was used as a positive control for the histochemical stains. RESULTS Overall, 35 of 40 nephrectomies contained microscopical deposits of oxalate, which were identified in 34 cases by their characteristic birefringency at light microscopy using a polarized filter, and in 27 cases by positive staining with Yasue’s silver reaction (Table 1). One of the latter cases had been classified as negative using polarization micros- copy. Crystals appeared to involve mainly the lumina of distal tubules (Fig 1A, C), or were located, but not always confined, to the cell cytoplasm of the tubular lining epithe- lium (Fig 1B). In some instances, the crystals appeared to have outgrown into the renal interstitium from partially destroyed tubules. In two cases, they were observed along the inner surface of the Bowman’s capsule (Fig 1D) or within mesangial cells. Calcium hydroxyapatite concretions were stained posi- tively with alizarin red and von Kossa’s method in seven instances, six of which had also proved to contain calcium oxalates (Table 1). With regard to the clinical parameters examined, oxalates were detected in nine of the 12 female and 26 of the 28 male patients (mean age 31.7 years). Fourteen of the kidneys were explanted for acute irreversible rejection, 14 for chronic rejection, four for ischemic necrosis, two for pielo- nephritis, and one for allergic microangiopathy. All five negative cases were cadaveric kidney transplant recipients (mean age 43.4 years), who were explanted from 2 days to 11 years postoperatively for acute rejection (three cases), or chronic rejection or ischemic necrosis of the graft (one case each). One of them had been treated with azathioprine immunosuppression. DISCUSSION The presence of occasional oxalate crystals is not an uncommon finding in native kidneys damaged by various diseases. Factors influencing urinary stone formation in kidney-transplanted patients have been recognised and include urinary tract infection, hypercalcemia-induced hy- percalciuria, or surgical complications. 4 However, in a large American series of 892 renal transplants, the incidence of symptomatic upper urinary tract calculi has been as low as 1.1%. 5 The incidence of asymptomatic microscopical cal- cium oxalate deposits in kidney-transplanted patients has not been thoroughly investigated. Olsen et al 6 compared From the Dipartimento di Medicina Sperimentale e Patologia (L.M., I.P., A.C., G.S., I.D-N., U.D-T.), and II Patologia Chirurgica STO (R.C.), Universita ` degli Studi “La Sapienza,” Rome, Italy. Address reprint requests to Dr I. Pecorella, Universita ` degli Studi “La Sapienza,” Dipartimento di Medicina Sperimentale e Patologia, Viale Regina Elena 324, 00161 Rome, Italy. 0041-1345/01/$–see front matter © 2001 by Elsevier Science Inc. PII S0041-1345(00)02470-2 655 Avenue of the Americas, New York, NY 10010 1262 Transplantation Proceedings, 33, 1262–1265 (2001)