What are the key features to evaluate when examining a kidney pathology slide, including tubular and basement membrane changes, to accurately interpret the results and diagnose renal pathology?

From the Guidelines

To accurately interpret kidney pathology slides, it is essential to evaluate the glomeruli for hypercellularity, basement membrane thickening, or crescent formation, and assess the tubules for acute tubular necrosis, casts, or crystals, as well as the interstitium for inflammation or fibrosis, as recommended by the Mayo Clinic/Renal Pathology Society consensus report 1. When examining a kidney pathology slide, the following key features should be evaluated:

• Glomeruli:
  • Hypercellularity
  • Basement membrane thickening
  • Crescent formation
  • Mesangial expansion and capillary wall thickening
  • Intracapillary fibrin thrombi, hyaline thrombi, and wire loops
• Tubules and interstitium:
  • Acute tubular injury
  • Tubular basement abnormalities, such as IFTA (interstitial fibrosis and tubular atrophy)
  • Interstitial inflammation and fibrosis
• Vasculature:
  • Arterial hyalinosis
  • Fibrinoid necrosis Special stains, such as PAS, silver, and Congo red, and immunofluorescence, are crucial for distinguishing between different types of glomerulonephritis and other renal diseases 1. Electron microscopy is also essential for precise diagnosis, particularly in cases of membranous nephropathy, lupus nephritis, or minimal change disease 1. Always correlate microscopic findings with clinical information and laboratory data for accurate interpretation, as emphasized in the Mayo Clinic/Renal Pathology Society consensus report 1. The primary diagnosis should include the disease entity/pathogenic type, pattern of injury, and score/grade/class for disease entities, such as IgA nephropathy, lupus nephritis, and ANCA GN, as recommended by the consensus report 1. Secondary diagnoses should be reported separately and include coexisting lesions that do not form the primary diagnosis. Guidelines for the report format, light microscopy, immunofluorescence microscopy, electron microscopy, and ancillary studies are also provided in the consensus report 1.

From the Research

Key Features to Evaluate in Kidney Pathology Slides

When examining a kidney pathology slide, several key features should be evaluated to accurately interpret the results and diagnose renal pathology. These features include:

• Tubular changes:
  • Tubular injury, such as necrotic tubules or tubules with casts, can be identified using deep-learning models 2
  • Tubular atrophy, which can have various morphologic appearances, including "classic" atrophic tubules, "thyroidization", and "endocrine" tubules 3
• Basement membrane changes:
  • Glomerular basement membrane (GBM) thickening, which is considered one of the earliest detectable pathological features of diabetic nephropathy 4
  • Tubular basement membrane (TBM) changes, such as thickening or deposition of immunoglobulins, can be observed in diabetic nephropathy 5
• Other features:
  • Interstitial changes, such as the presence of interstitial collagens or isolated cells with epithelial characteristics 6, 3
  • Glomerular changes, such as mesangial matrix expansion or nodular lesions, can be observed in diabetic nephropathy 6

Evaluating Tubular and Basement Membrane Changes

To evaluate tubular and basement membrane changes, the following should be considered:

• The use of deep-learning models can assist in the histopathological diagnosis of acute kidney injury and identify tubular-specific injuries 2
• The thickness of the GBM can be estimated using direct measurements, and its relationship with renal outcomes in patients with diabetic nephropathy can be assessed 4
• The composition of the extracellular matrix in the glomeruli can be analyzed using immunohistochemical means to identify changes in the basement membrane components 6
• The presence of immunoglobulin deposition on the TBM can be observed using immunofluorescence studies, and its relationship with diabetic nephropathy can be evaluated 5