The goal of this observational cross-sectional study is to develop a clinical diagnostic system for intrinsic acute kidney disease (AKD) to help clincians make non-invasive diagnosis when a kidney biopsy is not available. The main questions it aims to answer are:

1. Can a clinical model comprised of common clinical indexes help diagnose AKD ?
2. Can a combinition of several urinary biomarkers help diagnose AKD ? The study will be conducted in retrospective cohorts of patients with AKD undergoing kidney biopsy. The gold standard of the study is histological diagnosis of AKD. The model will be developed in a derivation cohort from one center, and will be further externally validated in a multicent cohort. The urinary biomarkers will only be tested in the derivation cohort.

Acute kidney disease is a frequent syndrome characterized by a sudden loss of kidney function. AKD caused by intrinsic kidney diseases are usually more severe than other causes. The treatment of intrinsic AKD mostly depends on a definite pathological diagnosis, requiring invasive kidney biopsy which is not available in all AKD cases. The goal of this study is to develop a clinical diagnostic system comprised of clinical model and urinary biomarkers for intrinsic AKD to help clincians make non-invasive diagnosis.

Inclusion Criteria:

• Adult patients with AKD undergoing kidney biopsy between Jan. 1, 2020 and Dec. 31, 2024.

Exclusion Criteria:

• Patients were excluede if they

  1. underwent a biopsy to evaluate renal allograft rejection;
  2. had a history of hematopoietic stem cell transplantation;
  3. were diagnosed with hematological malignancy or end-stage tumor with kidney metastasis;
  4. were tested antineutrophil cytoplasmic autoantibody (ANCA) or double-strand DNA (dsDNA) or anti-glomerular basement membrane (GBM) antibody positive before biopsy.

Adult patients with AKD undergoing kidney biopsy between Jan. 1, 2020 and Apr. 30, 2024.