Kidney oxalate crystal deposition in adult patients: A relatively common finding
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AIMS: We aim to describe the clinical and histological findings in patients with the finding of any tubular oxalate deposits in kidney biopsy specimens.

BACKGROUND: The prevalence, manifestation, and outcome of secondary oxalate nephropathy have not been extensively studied.

MATERIALS AND METHODS: In this retrospective cohort study, we analyzed the clinical and histological findings in all patients with the finding of any tubular oxalate deposits in kidney biopsy specimens between July 1, 2017, and December 31, 2018, at Northwell Health Pathology Department (Manhasset, NY, USA).

RESULTS: The prevalence of oxalate deposition on a kidney biopsy was 4.07% (25/615), and in 88% of cases was a major finding. Prior to biopsy, oxalate was anticipated in only 1 case. The etiology of oxalosis was clarified retrospectively in 14 cases, most commonly due to GI surgery (n = 10) and increased oxalate intake (n = 4). In 11 cases, etiology remained unknown, although at least 3 cases were exposed to antibiotics associated with secondary oxalosis. There was no significant clinical/pathological or survival difference between known vs. unknown cause groups. The overall 3-month renal survival rate was 76.0 ± 8.5%. Multivariate Cox regression showed that creatinine at the time of biopsy (HR: 1.79, 95% CI: 0.71 - 4.51), background histological chronicity change (HR: 1.82, 95% CI: 0.70 - 4.72) and oxalate density (HR: 2.27, 95% CI: 0.49 - 10.55) are associated with end-stage kidney disease.

CONCLUSION: Oxalate deposition is common but rarely anticipated biopsy finding. Nephrologists need to consider surgical history and other secondary causes of oxalosis as causes of acute kidney injury and chronic kidney disease.