Kidney I for NEET PG Pathology: AKI, CKD, Nephritic and Nephrotic Syndrome, Glomerulonephritis, IgA, RPGN, Lupus and Diabetic Nephropathy

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🎯 Exam priority: High. Expect: nephritic vs nephrotic, the biopsy hallmark of each glomerular disease (foot processes, spikes, humps, linear IgG, crescents, Kimmelstiel-Wilson), IgA vs post-infectious timing, lupus classes, AKI criteria and prerenal vs tubular indices, and the casts of CKD.

CBME mapping: PA 27.2–27.7. Tubules, infection, cysts, stones and tumours are in article 22; amyloid kidney in article 6; urine examination in article 16.

Nephritic vs nephrotic syndrome, glomerular diseases, AKI and CKD. Drawn by TrackNation.

Acute and Chronic Kidney Injury

• AKI: a fall in kidney function over days to weeks with azotaemia. KDIGO definition — creatinine up ≥ 0.3 mg/dL within 48 hours, or ≥ 1.5 times baseline within 7 days, or urine < 0.5 mL/kg/h for 6 hours. Causes are prerenal (poor perfusion), renal (intrinsic) or postrenal (obstruction). Prerenal AKI and acute tubular injury are the commonest in hospital.

• Tubular injury gives tubular cells and many brown granular casts; urinary eosinophils hint at allergic interstitial nephritis.

• CKD: eGFR < 60 mL/min/1.73 m² for ≥ 3 months is the most reliable evidence; small kidneys on ultrasound favour CKD. Commonest causes: diabetic nephropathy, then hypertensive nephrosclerosis. Broad and waxy casts mark advanced failure.

• CKD complications: normocytic normochromic anaemia (too little erythropoietin); less calcitriol → low calcium, phosphate retention, secondary hyperparathyroidism and renal osteodystrophy.

Nephrotic Syndrome

• Definition: protein > 3 g/day from a glomerular disorder, with oedema and hypoalbuminaemia. Lipiduria (oval fat bodies, fatty casts). Loss of antithrombin III → clots, especially renal vein thrombosis.

• Minimal change disease: 70–90% of nephrotic syndrome in children over 1 year; diffuse effacement of foot processes on electron microscopy; steroid responsive. Rare secondary causes: NSAIDs, Hodgkin lymphoma.

• FSGS: sclerosis begins in some (focal) glomeruli and in part of each tuft (segmental); commonest primary nephrotic syndrome in US adults. Secondary: heroin, HIV, obesity, sickle cell disease. HIV-associated nephropathy shows the collapsing variant.

• Membranous nephropathy: an adult disease; target antigen PLA2R on podocytes. Subepithelial deposits with spikes of basement membrane between them. Secondary to drugs, infections, autoimmunity, cancer.

• MPGN: thickened GBM with double contours; immune-complex or complement-mediated (C3 GN, dense deposit disease).

• Diabetic nephropathy: commonest cause of nephrotic syndrome in adults and of kidney failure worldwide. Early hyperfiltration; thick GBM; nodular glomerulosclerosis = Kimmelstiel-Wilson lesions; hyalinosis of both afferent and efferent arterioles.

Nephritic Syndrome and RPGN

• Definition: haematuria with dysmorphic red cells and often red cell casts, variable proteinuria.

• Post-infectious GN: commonest acute GN in children 3–15 years; nephritogenic group A streptococci (pharyngitis or impetigo strains) after a latency of 6–21 days. Cola-coloured urine, oedema, hypertension. Subepithelial humps on EM; low C3 that normalises within 6–8 weeks in 80%.

• IgA nephropathy: commonest GN worldwide. Poorly glycosylated IgA1 binds mesangial cells. Gross haematuria 1–2 days after a mucosal infection — a shorter latency than post-infectious GN.

• RPGN: nephritic syndrome with glomerular crescents and kidney failure in weeks to months. By immunofluorescence: anti-GBM (~20%, linear IgG; Goodpasture when the lung bleeds too — antibody against type IV collagen), immune complex (~50%; post-infectious, IgA, lupus and others) and pauci-immune (~30%, ANCA vasculitis such as granulomatosis with polyangiitis).

• Lupus nephritis: class I minimal, II mesangial, III focal (< 50% glomeruli), IV diffuse (> 50%, commonest), V membranous (nephrotic), VI sclerosing. Wire loops are an activity lesion.

• Hereditary: Alport syndrome (type IV collagen gene, mostly X-linked, with sensorineural deafness and eye changes); thin basement membrane disease (GBM 150–225 nm instead of 300–400 nm; isolated microscopic haematuria).

Traps the Examiner Sets

• Haematuria 1–2 days after a cold = IgA; 1–3 weeks after a sore throat or skin infection = post-infectious GN.

• Linear IgG = anti-GBM; immune-complex deposits = immune-complex GN; few or none = pauci-immune (ANCA).

• Spikes = membranous; humps = post-infectious; foot processes only = minimal change.

• FENa < 1% = prerenal; > 1% = tubular injury.

• Waxy and broad casts = advanced CKD; red cell casts = glomerulonephritis.

Memory Hooks & Shortcuts

Shortcuts to lock in this article's numbers and lists. Each one only re-packages facts proven above.

• 🧠 IgA comes In A day (1–2 days); strep takes three weeks — IgA vs PIGN latency

• 🧠 Spikes for Membranous, Humps for Post-strep, Foot processes for Minimal change — EM hallmarks

• 🧠 Linear = Lung + kidney (anti-GBM) — Goodpasture

• 🧠 Kimmelstiel-Wilson = Kandy (diabetes) nodules — diabetic nephropathy

• 🧠 Waxy = Way past it (advanced CKD) — casts

• 🧠 Prerenal Preserves sodium (FENa < 1%) — AKI indices

Rapid-Revision Cards

• AKI (KDIGO)

  Cr ↑ ≥ 0.3 mg/dL in 48 h, or ≥ 1.5× in 7 d, or urine < 0.5 mL/kg/h × 6 h.

• Prerenal indices

  Urine Na < 10, FENa < 1%, BUN/Cr > 20.

• Tubular injury

  FENa > 1%; brown granular casts.

• CKD

  eGFR < 60 for ≥ 3 months; small kidneys.

• CKD casts

  Broad and waxy.

• CKD anaemia

  Normocytic; low erythropoietin.

• CKD calcium

  Low calcitriol → hypocalcaemia.

• Nephrotic

  > 3 g/day, oedema, low albumin, lipiduria.

• Nephrotic clot

  Renal vein thrombosis; AT-III loss.

• Minimal change

  Children; foot-process effacement; steroids; Hodgkin.

• FSGS

  Adults (US); heroin, HIV, obesity, sickle.

• HIVAN

  Collapsing FSGS.

• Membranous

  Adults; PLA2R; subepithelial spikes.

• MPGN

  Double-contour GBM.

• Diabetic kidney

  Kimmelstiel-Wilson nodules; afferent + efferent hyalinosis.

• Nephritic

  Haematuria, dysmorphic RBCs, RBC casts.

• PIGN

  6–21 days after strep; humps; low C3.

• IgA nephropathy

  Commonest GN; haematuria 1–2 days after URTI.

• RPGN

  Crescents; anti-GBM 20%, IC 50%, pauci 30%.

• Anti-GBM

  Linear IgG; type IV collagen; lung + kidney.

• Lupus nephritis

  Class IV diffuse commonest; V membranous.

• Alport

  Type IV collagen; X-linked; deafness.

• Thin GBM

  150–225 nm; benign haematuria.

Sources

Facts in this article were checked against these documents.

• MSD Manual Professional: Acute Kidney Injury; Chronic Kidney Disease — Merck & Co. (MSD Manuals), reviewed 2026 (link)

• MSD Manual Professional: Glomerular Disorders (nephritic and nephrotic overviews, PIGN, IgA nephropathy, RPGN, minimal change disease, FSGS, membranous nephropathy, MPGN, diabetic nephropathy, lupus nephritis, Alport syndrome, thin basement membrane disease, HIV-associated nephropathy) — Merck & Co. (MSD Manuals), reviewed 2025–26 (link)

• MSD Manual Professional: Anti-Glomerular Basement Membrane Disease — Merck & Co. (MSD Manuals), reviewed 2025 (link)

• Competency Based Undergraduate Curriculum, Pathology (PA 27) — National Medical Commission, 2024

Test Yourself: Practice Questions

Thirty-two questions in NEET PG style, most of them clinical vignettes.

Practice Questions (NEET PG pattern)

Original questions written in the style of the exam: +4 for a correct answer, −1 for a wrong one. Every answer was checked against the sources listed above. NEET PG papers are not published by NBEMS, so these are not past-paper questions.

Q1. A hospital patient's creatinine rises from 1.0 to 1.4 mg/dL within 48 hours. By KDIGO criteria this is

• (a) normal variation

• (b) chronic kidney disease

• (c) nephrotic syndrome

• (d) acute kidney injury

Q2. An oliguric patient after severe diarrhoea has urine sodium 8 mmol/L, FENa 0.5% and BUN/creatinine ratio 25. The AKI is most likely

• (a) acute tubular injury

• (b) postrenal obstruction

• (c) prerenal

• (d) acute interstitial nephritis

Q3. Urine sediment shows tubular epithelial cells and many brown granular casts in an oliguric patient after prolonged hypotension. This points to

• (a) IgA nephropathy

• (b) prerenal azotaemia

• (c) minimal change disease

• (d) acute tubular injury

Q4. The most reliable evidence that kidney disease is chronic rather than acute is

• (a) eGFR below 60 for at least 3 months

• (b) oliguria

• (c) a single high creatinine

• (d) red cell casts

Q5. Urine from a patient with advanced renal failure shows broad, highly refractile casts. They are

• (a) white cell casts

• (b) waxy casts

• (c) red cell casts

• (d) hyaline casts only

Q6. A patient with stage 4 CKD has haematocrit 25%, normal MCV and normal MCHC. The main cause is

• (a) iron deficiency always

• (b) haemolysis

• (c) deficient erythropoietin production

• (d) B12 deficiency

Q7. Hypocalcaemia in CKD is mainly due to

• (a) excess vitamin D

• (b) reduced renal production of calcitriol

• (c) low phosphate

• (d) excess PTH

Q8. The two commonest causes of CKD, in order, are

• (a) lupus, then IgA

• (b) polycystic kidney, then stones

• (c) TB, then amyloid

• (d) diabetic nephropathy, then hypertensive nephrosclerosis

Q9. A 4-year-old has oedema, urine protein over 3 g/day, a non-nephritic sediment and normal kidney function. Electron microscopy shows diffuse effacement of podocyte foot processes. The diagnosis is

• (a) post-infectious GN

• (b) membranous nephropathy

• (c) Alport syndrome

• (d) minimal change disease

Q10. A patient with Hodgkin lymphoma develops nephrotic syndrome. The glomerular lesion classically associated is

• (a) anti-GBM disease

• (b) membranous nephropathy

• (c) IgA nephropathy

• (d) minimal change disease

Q11. Nephrotic syndrome is defined by proteinuria above

• (a) 1 g/day

• (b) 30 mg/g creatinine

• (c) 150 mg/day

• (d) 3 g/day with oedema and hypoalbuminaemia

Q12. The thrombotic complication especially typical of nephrotic syndrome is

• (a) renal vein thrombosis

• (b) papillary necrosis

• (c) pyelonephritis

• (d) renal stone

Q13. Urine microscopy in nephrotic syndrome shows tubular cells packed with lipid. These are

• (a) clue cells

• (b) red cell casts

• (c) waxy casts

• (d) oval fat bodies

Q14. Biopsy from an adult with nephrotic syndrome shows subepithelial deposits with spikes of basement membrane between them; serum anti-PLA2R antibody is positive. The diagnosis is

• (a) FSGS

• (b) membranous nephropathy

• (c) MPGN

• (d) minimal change disease

Q15. A patient with HIV infection and heavy proteinuria has a biopsy showing collapsing glomerulopathy. This is a variant of

• (a) IgA nephropathy

• (b) focal segmental glomerulosclerosis

• (c) membranous nephropathy

• (d) MPGN

Q16. Secondary FSGS is associated with all of the following EXCEPT

• (a) IgA vasculitis as the main cause

• (b) obesity

• (c) sickle cell disease

• (d) heroin use

Q17. A silver stain of a glomerulus shows a thickened basement membrane with a double contour ('tram track'). The pattern is

• (a) diabetic nephropathy

• (b) thin basement membrane disease

• (c) minimal change disease

• (d) membranoproliferative glomerulonephritis

Q18. Kidney biopsy from a long-standing diabetic shows rounded nodules of mesangial matrix and hyalinosis of both afferent and efferent arterioles. The nodules are

• (a) crescents

• (b) wire loops

• (c) humps

• (d) Kimmelstiel-Wilson lesions

Q19. The commonest cause of kidney failure worldwide is

• (a) polycystic kidney disease

• (b) IgA nephropathy

• (c) diabetic nephropathy

• (d) lupus nephritis

Q20. Two weeks after a streptococcal sore throat, a 7-year-old passes cola-coloured urine and has oedema and hypertension. Which finding is expected?

• (a) normal complement with IgA deposits

• (b) linear IgG on immunofluorescence

• (c) positive anti-PLA2R

• (d) low serum C3

Q21. Electron microscopy in post-streptococcal glomerulonephritis typically shows

• (a) spikes

• (b) foot-process effacement only

• (c) linear deposits

• (d) hump-shaped subepithelial immune complex deposits

Q22. A man has recurrent gross haematuria; the latest episode began one day after an upper respiratory infection. The likely diagnosis is

• (a) post-streptococcal GN

• (b) minimal change disease

• (c) membranous nephropathy

• (d) IgA nephropathy

Q23. The commonest form of glomerulonephritis worldwide is

• (a) post-streptococcal GN

• (b) IgA nephropathy

• (c) anti-GBM disease

• (d) lupus nephritis

Q24. Rapidly progressive glomerulonephritis is defined histologically by

• (a) foot-process effacement

• (b) Kimmelstiel-Wilson nodules

• (c) thin basement membrane

• (d) glomerular crescents

Q25. A smoker has haemoptysis and rapidly rising creatinine. Immunofluorescence of the kidney shows linear IgG along the GBM. The antibody targets

• (a) neutrophil proteinase 3

• (b) PLA2R

• (c) double-stranded DNA

• (d) type IV collagen of basement membranes

Q26. RPGN with crescents but few or no immune deposits on immunofluorescence is usually due to

• (a) post-streptococcal GN

• (b) ANCA-associated vasculitis

• (c) anti-GBM antibody

• (d) lupus

Q27. The commonest class of lupus nephritis, with proliferation in more than half the glomeruli, is

• (a) class VI (sclerosing)

• (b) class I (minimal mesangial)

• (c) class IV (diffuse)

• (d) class II (mesangial)

Q28. A boy has haematuria, progressive kidney disease and high-frequency sensorineural hearing loss; his maternal uncle had kidney failure. The defective protein is

• (a) fibrillin

• (b) nephrin only

• (c) type IV collagen

• (d) polycystin

Q29. A healthy adult has isolated microscopic haematuria and normal kidney function; electron microscopy shows a GBM about 200 nm wide. The diagnosis is

• (a) Alport syndrome

• (b) IgA nephropathy

• (c) minimal change disease

• (d) thin basement membrane disease

Q30. Nephritic syndrome is characterised by

• (a) proteinuria > 3 g/day with lipiduria

• (b) glycosuria

• (c) haematuria with dysmorphic red cells and red cell casts

• (d) pyuria with white cell casts

Q31. Membranous nephropathy is best described as

• (a) a crescentic GN

• (b) mainly an adult disease, often secondary to drugs, infections, autoimmunity or cancer

• (c) the commonest nephrotic syndrome of young children

• (d) a hereditary collagen disease

Q32. The commonest cause of primary nephrotic syndrome in adults (US data) is

• (a) post-infectious GN

• (b) focal segmental glomerulosclerosis

• (c) IgA nephropathy

• (d) minimal change disease

Active Recall

From memory: define AKI by KDIGO and separate prerenal from tubular injury; define CKD and list its casts, anaemia and mineral changes; contrast nephritic and nephrotic syndrome; give the biopsy hallmark of minimal change, FSGS, membranous, MPGN and diabetic nephropathy; contrast IgA and post-infectious GN; classify RPGN by immunofluorescence; and name the commonest lupus class and the Alport defect.