Renal Biopsy Interpretation Primer

Educational module for kidney biopsy interpretation and diagnostic reasoning

IgA Nephropathy

Nephritic Syndrome

Light Microscopy (LM)

Mesangial proliferation, IgA deposits

Immunofluorescence (IF)

IgA (dominant), C3

Electron Microscopy (EM)

Mesangial electron-dense deposits

Clinical Presentation

Hematuria (gross or microscopic), proteinuria, normal complement

💡 Diagnostic Pearl

Most common primary GN worldwide; IgA-dominant on IF is diagnostic

Post-Streptococcal GN

Nephritic Syndrome

Light Microscopy (LM)

Endocapillary proliferation, 'starry sky' appearance

Immunofluorescence (IF)

IgG, C3 (C3 dominant), C1q

Electron Microscopy (EM)

Subepithelial 'humps' (pathognomonic)

Clinical Presentation

Hematuria, RBC casts, hypertension, low C3, normal C4

💡 Diagnostic Pearl

Subepithelial humps on EM are pathognomonic; C3 returns to normal in weeks

ANCA-Associated GN

Nephritic Syndrome

Light Microscopy (LM)

Necrotizing GN with crescent formation, minimal immune deposits

Immunofluorescence (IF)

ANCA (MPO or PR3), minimal Ig

Electron Microscopy (EM)

Sparse or absent deposits (pauci-immune)

Clinical Presentation

Rapidly progressive GN, systemic vasculitis, positive ANCA

💡 Diagnostic Pearl

Pauci-immune pattern on IF; ANCA serology confirms diagnosis

Anti-GBM Disease

Nephritic Syndrome

Light Microscopy (LM)

Necrotizing GN with crescent formation

Immunofluorescence (IF)

IgG linear along GBM (pathognomonic)

Electron Microscopy (EM)

Electron-dense deposits along GBM

Clinical Presentation

Rapidly progressive GN, possible pulmonary hemorrhage (Goodpasture)

💡 Diagnostic Pearl

Linear IgG on IF is diagnostic; anti-GBM serology confirms

Membranous Nephropathy

Nephrotic Syndrome

Light Microscopy (LM)

Thickened GBM, 'spike and dome' appearance

Immunofluorescence (IF)

IgG, C3 (IgG dominant)

Electron Microscopy (EM)

Subepithelial electron-dense deposits, 'spike and dome'

Clinical Presentation

Heavy proteinuria, nephrotic syndrome, normal complement, normal creatinine

💡 Diagnostic Pearl

Spikes and domes on EM are diagnostic; check PLA2R and THSD7A antibodies

Focal Segmental Glomerulosclerosis (FSGS)

Nephrotic Syndrome

Light Microscopy (LM)

Focal segmental sclerosis, hyalinosis

Immunofluorescence (IF)

IgM, C3 (non-specific)

Electron Microscopy (EM)

Foot process effacement

Clinical Presentation

Heavy proteinuria, nephrotic syndrome, hematuria, hypertension

💡 Diagnostic Pearl

Podocyte injury; check for secondary causes (HIV, heroin, obesity)

Minimal Change Disease

Nephrotic Syndrome

Light Microscopy (LM)

Normal glomeruli on light microscopy

Immunofluorescence (IF)

Negative or trace (non-specific)

Electron Microscopy (EM)

Foot process effacement (only finding)

Clinical Presentation

Pure nephrotic syndrome, normal creatinine, normal complement, selective proteinuria

💡 Diagnostic Pearl

EM shows foot process effacement; most common cause of nephrotic syndrome in children

Membranoproliferative GN (MPGN)

Nephritic Syndrome

Light Microscopy (LM)

Mesangial proliferation, GBM duplication ('tram-track')

Immunofluorescence (IF)

C3 (dominant), IgG, IgM

Electron Microscopy (EM)

Subendothelial deposits, GBM duplication

Clinical Presentation

Hematuria, proteinuria, low C3, normal C4

💡 Diagnostic Pearl

C3-dominant pattern; check for C3 nephrotic factor, hepatitis C

Lupus Nephritis

Nephritic Syndrome

Light Microscopy (LM)

Variable (Class I-VI); 'wire loop' lesions, hyaline thrombi

Immunofluorescence (IF)

IgG, IgA, IgM, C1q, C3 ('full house')

Electron Microscopy (EM)

Subendothelial and subepithelial deposits

Clinical Presentation

Hematuria, proteinuria, low C3/C4, positive ANA/anti-dsDNA

💡 Diagnostic Pearl

'Full house' IF pattern is highly specific; classify by WHO class

Acute Tubular Necrosis (ATN)

Tubulointerstitial Syndrome

Light Microscopy (LM)

Tubular epithelial cell necrosis, loss of brush border

Immunofluorescence (IF)

Negative or non-specific

Electron Microscopy (EM)

Mitochondrial swelling, loss of brush border

Clinical Presentation

Acute rise in creatinine, FENa >2%, muddy brown casts

💡 Diagnostic Pearl

Most common cause of intrinsic AKI; usually reversible

Acute Interstitial Nephritis (AIN)

Tubulointerstitial Syndrome

Light Microscopy (LM)

Interstitial edema, infiltration with lymphocytes

Immunofluorescence (IF)

IgG, IgM (variable)

Electron Microscopy (EM)

No specific findings

Clinical Presentation

Drug-induced (NSAIDs, antibiotics), fever, rash, eosinophiluria

💡 Diagnostic Pearl

Classic triad: fever, rash, eosinophiluria; discontinue offending drug

Thrombotic Microangiopathy (TMA)

Vascular Syndrome

Light Microscopy (LM)

Arteriolar necrosis, fibrinoid necrosis, RBC fragmentation

Immunofluorescence (IF)

Fibrin deposits

Electron Microscopy (EM)

Endothelial swelling, RBC fragmentation

Clinical Presentation

Microangiopathic hemolytic anemia, thrombocytopenia, AKI (HUS/TTP triad)

💡 Diagnostic Pearl

Check ADAMTS13 (deficient in TTP); Shiga toxin in HUS

Hypertensive Nephrosclerosis

Vascular Syndrome

Light Microscopy (LM)

Arteriolar hyalinosis, glomerular sclerosis

Immunofluorescence (IF)

Negative or non-specific

Electron Microscopy (EM)

Arteriolar hyalinosis

Clinical Presentation

Chronic HTN, proteinuria <1 g/day, normal complement

💡 Diagnostic Pearl

Diagnosis of exclusion; requires clinical correlation with HTN history

Amyloid Nephropathy

Nephrotic Syndrome

Light Microscopy (LM)

Amorphous deposits in glomeruli (Congo red positive, apple-green birefringence)

Immunofluorescence (IF)

Amyloid (light chain restricted)

Electron Microscopy (EM)

Fibrils (7-10 nm diameter)

Clinical Presentation

Heavy proteinuria, nephrotic syndrome, systemic amyloidosis

💡 Diagnostic Pearl

Congo red stain with apple-green birefringence is diagnostic

Educational Disclaimer: This tool is for educational purposes only. Kidney biopsy interpretation requires expert pathology review. Always correlate biopsy findings with clinical presentation, serologies, and imaging. This primer is not a substitute for professional pathology interpretation.

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