The Spectrum of Biopsy-Proven Kidney Diseases, Causes, and Renal Outcomes in Acute Kidney Injury Patients.

INTRODUCTION: Acute kidney injury (AKI) is a group of highly heterogeneous, complicated clinical syndromes. Although kidney biopsy plays an irreplaceable role in evaluating complex AKI, a few studies have focused on the clinicopathology of AKI biopsies. This study analyzed the pathological disease spectrum, causes, and renal outcomes of biopsied AKI patients. METHODS: We retrospectively included 2,027 AKI patients who underwent kidney biopsies at a national clinical research center of kidney diseases from 2013 through 2018. To compare the biopsied AKI cases without and with coexisting glomerulopathy, patients were classified into acute tubular/tubulointerstitial nephropathy-associated AKI (ATIN-AKI) and glomerular disease-associated AKI (GD-AKI) groups. RESULTS: Of 2,027 biopsied AKI patients, 65.1% were male, with a median age of 43 years. A total of 1,590 (78.4%) patients had coexisting GD, while only 437 (21.6%) patients had ATIN alone. The AKI patients with GD mainly (53.5%) manifested as stage 1 AKI, while most ATIN-AKI patients (74.8%) had stage 3 AKI. In the ATIN-AKI group, 256 (58.6%) patients had acute interstitial nephritis (AIN), and 77 (17.6%) had acute tubular injury (ATI). ATIN-AKI was mainly caused by drugs in 85.5% of AIN and 63.6% of ATI cases, respectively. In AKI patients with coexisting GD, the leading pathological diagnoses in over 80% of patients were IgA nephropathy (IgAN, 22.5%), minimal change disease (MCD, 17.5%), focal segmental glomerulosclerosis (FSGS, 15.3%), lupus nephritis (LN, 11.9%), membranous nephropathy (MN, 10.2%), and ANCA-associated vasculitis (AAV, 4.7%). A total of 775 patients were followed up within 3 months after renal biopsy; ATIN-AKI patients achieved statistically higher complete renal recovery than the GD-AKI patients (83.5% vs. 70.5%, p < 0.001). CONCLUSIONS: Most biopsied AKI patients have coexisting GD, while ATIN alone is seen less frequently. ATIN-AKI is mainly caused by drugs. In GD-AKI patients, IgAN, MCD, FSGS, LN, MN, and AAV are the leading diagnoses. Compared to AKI patients without GD, patients with GD suffer from worse renal function recovery.

Secondary Oxalate Nephropathy: Causes and Clinicopathological Characteristics of a Case Series.

INTRODUCTION: Secondary oxalate nephropathy (OxN) is associated with a variety of causes and has not been well characterized in Chinese population. To investigate the etiology, clinicopathological features, and outcomes of secondary OxN, we report a case series from a single center in China. METHODS: A retrospective analysis of 68 patients diagnosed with secondary OxN by renal biopsy from January 2013 to February 2019 in Jinling Hospital was performed. RESULTS: Secondary OxN accounted for 0.23% of the renal biopsies and 2.31% of patients who received renal biopsies due to acute kidney injury (AKI). A total of 49 men and 19 women with an average age of 51.6 ± 11.8 years were enrolled. The most common cause was iatrogenic medication, followed by oxalate-rich diet and industry exposure. Stage 1, 2, and 3 AKI and AKI on chronic kidney disease (ACKD) were found in 4.4, 8.8, 69.1, and 17.6% of the patients, respectively. The peak serum creatinine during hospitalization was 8.62 ± 4.67 mg/dL. The median urinary oxalate excretion was 51.5 (23.2-147.1) mg/24 h. Kidney biopsy showed extensive calcium oxalate crystal deposits with acute tubulointerstitial nephritis. Thirty-four patients (50.0%) required renal replacement therapy. At the end of a follow-up that lasted 8.7 (0.1-72.1) months, 81.0% of patients achieved renal function recovery in 50 (14-432) days. Patients with renal function recovery had a lower rate of ACKD, a higher level of hemoglobin, a lower level of urine lysozyme, and a lower degree of interstitial fibrosis/tubular atrophy, interstitial inflammation, and global glomerulosclerosis than those in the nonrecovery group. CONCLUSIONS: In this case series of secondary OxN, the most common cause was iatrogenic medication, and it presented with AKI or ACKD. Half of the patients required renal replacement therapy, and in most of them, the renal function was reversible. Renal biopsy played an important role in diagnosis and prognosis evaluation.