Hyperoxaluria: The Diet before the Riot

Introduction: Oxalate nephropathy is a rare condition involving the accumulation of oxalate crystals within the nephrons. Primary hyperoxaluria involves enzymatic defects in the metabolism of glyoxylate, while secondary hyperoxaluria includes dietary and malabsorption related etiologies. Our case highlights the early diagnosis of oxalate nephropathy secondary to excessive intake of nuts and vitamin C. Case Description: A Caucasian male in his 80s presented to the hospital with an AKI on CKD stage 4 in the setting of a new antibiotic prescription. Creatinine had increased to 4.2mg/dL from a baseline of 2.2mg/dL, with no etiology identified on urinalysis or renal ultrasound. Renal biopsy revealed an acute tubular injury with intraluminal calcium oxalate crystals deposits, confirming a diagnosis of oxalate nephropathy (Fig. 1). A detailed history revealed excessive dietary intake of oxalate-rich foods, including nuts, and daily ingestion of 2g of vitamin C. The patient was counselled on adjusting his diet and stopping vitamin C supplementation which led his creatinine to return close to baseline 2-months post-discharge. Discussion: Dietary oxalate varies in individuals ranging from 44-351mg/day with there being a non-linear association between dietary and urinary oxalate content. The addition of 1000mg of vitamin C has also been shown to increase urinary oxalate up to 13mg/day. Consuming excessive amounts of oxalate can result in urinary levels above the threshold of 44mg/day for association with calcium oxalate stones. Our case emphasizes the possibility of excessive consumption of almonds, walnuts, peanuts, pine nuts and vitamin C as etiologies. The patient consumed approximately 30g of these nuts several times a day, which approximates 242mg of oxalate per serving. Additionally, our patient consumed 2000mg of Vitamin C daily. These factors played an integral part in the development of his AKI, highlighting the importance of collecting a thorough dietary history and keeping a low threshold to performing a kidney biopsy to prevent progression into ESKD.