The Clinical and Pathological Characteristics of Patients with Oxalate Nephropathy.

Key Points: Oxalate nephropathy is an underrecognized cause of CKD and ESKD. We present one of the largest native oxalate nephropathy cohorts to date from a tertiary care institution in the United States. Oxalate nephropathy has multiple etiologies and given its clinical course and poor prognosis, attention must be paid to screening for risk factors to guide prompt diagnosis and management.

Background: Oxalate nephropathy (ON) is characterized by deposition of calcium oxalate crystals in the kidney and is commonly under-recognized. 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 ON 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 (=12) or lack of data (=17). Thirty-one patients with native ON 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 =17 (54.8%) and diabetic glomerulosclerosis =7 (22.6%). Severe and moderate interstitial fibrosis was present in 38.7% (=12) and 51.6% (=16) of biopsies, respectively. Ten had a single etiology of ON, ten had a multifactorial etiology (both enteric hyperoxaluria and high precursor intake), and 11 had an unclear etiology. Notably, only seven 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 five were dialysis-free at presentation. Five of the 26 were deceased at 1 year, with 12 patients (38.7%) deceased at last follow-up. Seventeen patients received targeted management, while nine patients did not receive targeted treatment, and all nine required hemodialysis. More patients (31.6%) had vitamin C intake after the coronavirus disease 2019 pandemic (2020–2023) versus 16.7% before 2020.

Conclusions: ON 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 ON to aid prompt diagnosis and management.

Podcast: This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/K360/2024_01_26_KID0000000000000340.mp3