The Clinical and Pathological Characteristics of Patients with Oxalate Nephropathy.

BACKGROUND: Oxalate nephropathy (ON) is characterized by deposition of calcium oxalate crystals in the kidney and is commonly underrecognized. Causes of ON include primary hyperoxaluria, enteric hyperoxaluria and ingestion of excess oxalate or its precursors.

METHODS: We report the clinical and pathological characteristics of one of the largest series of native kidney oxalate nephropathy to date, from January 2015 to March 2023 at the Cleveland Clinic.

RESULTS: We identified 60 native biopsies with oxalate deposits and excluded patients with clinically insignificant biopsies (n=12) or lack of data (n=17). 31 patients with native oxalate nephropathy were described. The mean age at diagnosis was 66.2 years (±12.1) and 58.1% were female. 87.1% had hypertension, 58.1% had diabetes, 42% had nephrolithiasis, and 77.4% had underlying CKD with a mean baseline creatinine of 1.8 mg/dL ±1.3.The mean creatinine at biopsy was 5.2 mg/dL ±1.7. Kidney biopsies showed abundant calcium oxalate crystal deposits, and 27 of 31 biopsies had additional diagnoses, the most common of which were acute tubular injury n=17 (54.8%) and diabetic glomerulosclerosis n=7 (22.6%). Severe and moderate interstitial fibrosis was present in 38.7% (n=12) and 51.6% (n=16) of biopsies respectively. 10 had a single etiology of ON, 10 had a multifactorial etiology (both enteric hyperoxaluria and high precursor intake) and 11 had an unclear etiology. Notably, only 7 patients had a history of gastric bypass.The mean duration of follow-up was 26.8 months and 26 patients had follow up data >1 year. Of these, 21 required dialysis and 5 were dialysis free at presentation. 5 of the 26 were deceased at 1 year, with 12 patients (38.7%) deceased at last follow up. 17 patients received targeted management while 9 patients did not receive targeted treatment and all 9 required hemodialysis. More patients (31.6%) had vitamin C intake post COVID pandemic (2020-2023) vs 16.7% prior to 2020.

CONCLUSION: Oxalate nephropathy presents as AKI or acute on CKD. The prognosis is poor with most patients requiring dialysis at presentation with high morbidity and mortality. Clinicians need to be aware of the risk factors associated with oxalate nephropathy to aid prompt diagnosis and management.