SINGLE-CRYSTAL X-RAY DIFFRACTION (SC-XRD) AND SCANNING ELECTRON MICROSCOPY - ENERGY DISPERSIVE X-RAY ANALYSIS (SEM-EDX) FOR THE IDENTIFICATION OF CALCIUM OXALATE DEPOSITION IN A RENAL BIOPSY

Oxalate nephropathy is a rare entity with poor renal prognosis. When history of kidney stones and/or classical risk factors for secondary hyperoxaluria (such as bariatric surgery) are present, the diagnosis is easy. Sometimes the clinical onset is confusing and the diagnosis can be delayed, even if a renal biopsy is performed. We present the case of a 69-year-old man with history of type 2 diabetes and chronic kidney disease who presented with worsening renal function (creatinine 2 to 4 mg/dl), hyperkalemia and metabolic acidosis. Urine analysis showed mild proteinuria (200mg/day) and no crystals. Kidneys had normal volume and no stones were seen by ultrasonography. A renal biopsy showed mild nodular diabetic glomerulopathy and acute tubular injury with intratubular deposition of birefringent crystals (Figure 1A). Differential diagnosis included oxalate nephropathy and, less likely 2,8- dihydroxyadenine and urate crystals. Since conventional spectrometry could not be performed on single crystals due to their small size, we decided to investigate the crystals with the typical structural and compositional characterization techniques used in the field of Material Science, SC-XRD and SEM-EDX.