Glomerular Diseases

The glomerulus is a tuft of specialized capillaries that filters roughly 180 litres of plasma every day, letting water and small solutes through while holding back cells and albumin. When this exquisite filter is injured, the consequences are surprisingly predictable: either protein leaks out in massive amounts (nephrotic), or the filter tears and lets blood and inflammatory cells through (nephritic). Learning to read those two patterns — and knowing when only a biopsy can settle the question — is one of the most rewarding pattern-recognition skills in internal medicine.

This page teaches you to think like a nephrologist: start with the urine, place the patient on the nephrotic-nephritic spectrum, use serology to narrow the list, and understand why the kidney biopsy remains the arbiter.

Learning Objectives

• Distinguish nephrotic from nephritic syndrome by their defining urinary and clinical features.
• List the major primary and secondary causes of each syndrome and their typical patient profiles.
• Explain the pathophysiology of proteinuria, oedema, hematuria, and hypertension in glomerular disease.
• Interpret a basic glomerular serology panel (complement, ANA, ANCA, anti-GBM, anti-PLA2R).
• Describe how a renal biopsy is processed (light, immunofluorescence, electron microscopy) and why each arm matters.
• Recognise rapidly progressive glomerulonephritis as a nephrological emergency.

Quick Answer

Glomerular diseases injure the kidney's filtering tufts and present along a spectrum. The nephrotic end is dominated by heavy proteinuria (more than 3.5 g/day), hypoalbuminemia, oedema, and hyperlipidemia, with a relatively bland urine sediment — the filter is leaky but not acutely inflamed. The nephritic end is dominated by inflammation: hematuria with dysmorphic red cells and red-cell casts, hypertension, mild-to-moderate proteinuria, and falling kidney function. Glomerulonephritis (GN) is the inflammatory (nephritic-type) subgroup. Because many entities overlap and treatment differs sharply, the renal biopsy — read by light microscopy, immunofluorescence, and electron microscopy — is the definitive diagnostic tool once serology has narrowed the field.

Where It Came From

For most of medical history, dropsy (generalised swelling) was a symptom without a cause. The turning point came in 1827, when the London physician Richard Bright, working at Guy's Hospital, published Reports of Medical Cases. Bright made a simple but revolutionary correlation: patients who were swollen and whose urine coagulated when heated (albuminuria — he literally held urine over a candle flame) turned out, at autopsy, to have shrunken, granular, diseased kidneys. He had linked a clinical sign (protein in the urine), a laboratory finding, and a specific organ pathology for the first time. For nearly a century, chronic kidney disease of glomerular origin was simply called Bright's disease.

The motivation was practical and urgent: dropsy killed people, and physicians had no way to tell renal dropsy from cardiac or hepatic dropsy, let alone treat it. Bright's insight created a whole discipline — the study of what the urine reveals about the kidney.

Over the next century the single label "Bright's disease" fractured as tools improved. The percutaneous renal biopsy, pioneered by Iversen and Brun in Denmark in 1951 and refined by Robert Kark and Robert Muehrcke in Chicago, finally let clinicians see the living glomerulus. Add immunofluorescence (1960s) and electron microscopy, and the old catch-all dissolved into dozens of specific diseases — minimal change disease, membranous nephropathy, IgA nephropathy, lupus nephritis, and more. The need throughout was the same one Bright faced: match the pattern of injury to a treatable mechanism.

The Nephrotic–Nephritic Spectrum

Think of glomerular injury as a slider, not two boxes. At one extreme the filter's charge and size barrier fails without much inflammation; at the other, inflammatory cells and antibodies attack the capillary wall and it bleeds. Many real patients sit in between (a "nephritic-nephrotic" picture), which is exactly why we still biopsy.

Feature	Nephrotic syndrome	Nephritic syndrome
Core lesion	Podocyte / basement-membrane leak	Glomerular inflammation
Proteinuria	Heavy (more than 3.5 g/day)	Mild to moderate (usually less than 3 g/day)
Hematuria	Absent or minimal	Prominent, dysmorphic RBCs, RBC casts
Oedema	Marked, often periorbital and dependent	Present, often with hypertension
Blood pressure	Usually normal or mildly raised	Often high
Serum albumin	Low	Normal or mildly low
Kidney function	Often preserved early	Frequently declining
Urine sediment	Bland; oval fat bodies, fatty casts	Active; RBC casts the hallmark

Why the nephrotic patient swells and clots

Losing albumin lowers plasma oncotic pressure, but modern understanding adds a second mechanism: primary renal sodium retention via activation of the epithelial sodium channel. Both drive oedema. The liver responds to low albumin by overproducing lipoproteins, giving the classic hyperlipidemia. Critically, the kidney also spills anticoagulant proteins (antithrombin III) into the urine, creating a hypercoagulable state — renal vein thrombosis and pulmonary embolism are real dangers, especially in membranous nephropathy.

Major Nephrotic Diseases

• Minimal change disease (MCD) — the commonest cause in children. Light microscopy looks normal; electron microscopy shows diffuse podocyte foot-process effacement. Exquisitely steroid-responsive.
• Focal segmental glomerulosclerosis (FSGS) — scarring of some (focal) glomeruli in part (segmental) of the tuft. Common in adults, in people of African ancestry (APOL1 risk variants), and secondary to obesity, HIV, or reduced nephron mass. Less steroid-responsive.
• Membranous nephropathy — the classic adult primary nephrotic disease. Immune deposits along the outer basement membrane thicken the wall; roughly 70% are driven by autoantibodies against the podocyte antigen PLA2R, now measurable in blood. Watch for underlying malignancy or hepatitis B in secondary cases.
• Diabetic nephropathy — the single most common cause of nephrotic-range proteinuria overall, via mesangial expansion and Kimmelstiel-Wilson nodules.
• Amyloidosis — misfolded protein deposition; suspect in an older patient with heavy proteinuria and a monoclonal protein.

Major Nephritic Diseases (Glomerulonephritis)

• IgA nephropathy (Berger disease) — the world's commonest primary GN. Classically, a young adult develops visible hematuria within a day or two of a sore throat ("synpharyngitic"). Mesangial IgA deposits.
• Post-infectious (post-streptococcal) GN — a child, 1–3 weeks after a throat or skin streptococcal infection, with cola-coloured urine, oedema, hypertension, and low C3. Usually self-limiting.
• Lupus nephritis — protean; can be nephrotic, nephritic, or both. Low C3 and C4, positive ANA and anti-dsDNA. Biopsy class (I–VI) directly guides therapy.
• Anti-GBM disease (Goodpasture) — antibodies against basement-membrane collagen; kidney plus lung hemorrhage. A medical emergency treated with plasma exchange.
• ANCA-associated vasculitis — pauci-immune (little to see on immunofluorescence) crescentic GN in older adults, often with systemic vasculitis.

The emergency: rapidly progressive GN

When a nephritic patient loses kidney function over days to weeks, suspect rapidly progressive glomerulonephritis (RPGN), whose histological signature is crescents (proliferating cells filling Bowman's space). RPGN has three immunologic buckets — anti-GBM (linear IF), immune-complex (granular IF, e.g. lupus), and pauci-immune (ANCA). This is one of the few nephrology situations where you biopsy urgently and start immunosuppression fast, because nephrons are being lost by the hour.

Diagnosis: Reading the Urine, Then the Biopsy

Step 1 — the urine. A dipstick plus a microscope is the cheapest, most informative test in nephrology. Proteinuria is quantified with a spot urine protein-to-creatinine ratio. Dysmorphic red cells and red-cell casts mean glomerular bleeding — they point nephritic. Oval fat bodies and a bland sediment point nephrotic.

Step 2 — the blood. A focused serology panel narrows the differential dramatically:

Test	If abnormal, think
Low C3, normal C4	Post-infectious GN, C3 glomerulopathy
Low C3 and C4	Lupus nephritis, cryoglobulinemia
ANA / anti-dsDNA	Systemic lupus
ANCA (MPO/PR3)	Pauci-immune vasculitis
Anti-GBM	Goodpasture disease
Anti-PLA2R	Primary membranous nephropathy
Serum/urine electrophoresis	Amyloid, myeloma-related disease

Step 3 — the biopsy. A percutaneous needle biopsy under ultrasound guidance yields a core that is split three ways:

1. Light microscopy — the overall architecture: proliferation, crescents, sclerosis, thickening, nodules.
2. Immunofluorescence — what is deposited and where. Granular ("lumpy-bumpy") staining suggests immune complexes; linear staining suggests anti-GBM; absent/scant staining suggests pauci-immune ANCA disease; dominant IgA suggests IgA nephropathy.
3. Electron microscopy — the ultrastructure: foot-process effacement (MCD), subepithelial deposits and "spikes" (membranous), subepithelial humps (post-infectious).

Biopsy is generally deferred in children with a textbook steroid-responsive nephrotic presentation (assumed MCD) and in longstanding diabetics with a classic course — treat empirically, biopsy only if the story doesn't fit.

Worked example

A 24-year-old man has one day of brown urine two days after a sore throat. BP is 128/80, creatinine normal, urine shows dysmorphic RBCs, protein 0.8 g/day. C3 and C4 are normal. This is a nephritic picture; the synpharyngitic timing and normal complement fit IgA nephropathy far better than post-streptococcal GN (which lags 1–3 weeks and drops C3). Biopsy would confirm mesangial IgA. Contrast with a 6-year-old who, three weeks after impetigo, presents with facial puffiness, hypertension, cola-coloured urine, and low C3 — that is post-streptococcal GN, managed supportively.

Real-World Applications

• Primary care triage. A simple observation — is there blood and protein, or protein alone? — tells the GP whether to think inflammatory GN (urgent nephrology referral) versus a slower nephrotic process.
• Chronic disease prevention. Diabetic and hypertensive nephropathy are the leading causes of end-stage kidney disease worldwide; annual albumin-to-creatinine screening catches glomerular leak years before creatinine rises, when ACE inhibitors, ARBs, and SGLT2 inhibitors still change the trajectory.
• Oncology and infection links. Membranous nephropathy can herald an occult cancer; nephrotic syndrome in an adult warrants age-appropriate malignancy screening. Hepatitis B, hepatitis C, and HIV each map to specific glomerular lesions.
• Emergency medicine. Recognising RPGN (rising creatinine plus active urine plus systemic symptoms) and expediting biopsy and immunosuppression can be the difference between recovered and dialysis-dependent kidneys.

Common Mistakes

• "Protein on the dipstick means nephrotic syndrome." Wrong — trace or 1+ protein is common and non-specific. Nephrotic syndrome requires the full picture: heavy proteinuria (more than 3.5 g/day) plus hypoalbuminemia plus oedema. Always quantify.
• "Isolated microscopic hematuria needs urgent immunosuppression." Wrong — isolated glomerular hematuria with normal function and no proteinuria (often early IgA nephropathy or thin basement membrane disease) is usually monitored, not treated. Treatment intensity tracks proteinuria and kidney function, not the blood alone.
• "Post-streptococcal GN follows the sore throat immediately." Wrong — that immediate pattern is IgA nephropathy. Post-streptococcal GN has a latent period of 1–3 weeks and transiently low C3. Confusing the timing sends you down the wrong diagnostic path.
• "You can diagnose the specific glomerular disease from blood tests alone." Usually wrong. Serology narrows but rarely closes the differential; several diseases share low complement or overlapping presentations, so the biopsy remains the arbiter for most adults.

Comparison and Connections

The nephrotic-nephritic dichotomy is a teaching scaffold, not a rigid law — membranoproliferative GN and lupus nephritis routinely straddle both. What reliably separates the mechanisms is the biopsy immunofluorescence pattern:

IF pattern	Meaning	Example diseases
Granular ("lumpy-bumpy")	Immune-complex deposition	Lupus, post-infectious, membranous, IgA
Linear	Antibody against the GBM itself	Anti-GBM / Goodpasture
Pauci-immune (scant)	ANCA-driven, few deposits	Granulomatosis with polyangiitis, microscopic polyangiitis

Related concepts worth connecting: acute tubular injury and interstitial nephritis (non-glomerular causes of acute kidney injury), the complement cascade (immunology), and the renin-angiotensin system (why glomerular disease drives hypertension and why RAAS blockade protects the kidney).

Practice Questions

Recall

Q: What single urinary finding most specifically indicates glomerular bleeding? A: Red-cell casts (with dysmorphic red cells). Their presence localises the bleeding to the glomerulus rather than the lower tract.

Understanding

Q: Explain why a nephrotic patient is prone to thrombosis. A: The leaky glomerulus loses low-molecular-weight anticoagulant proteins — notably antithrombin III — into the urine, while the liver upregulates procoagulant factors alongside lipoproteins. The net effect is a hypercoagulable state, with renal vein thrombosis a classic complication, especially in membranous nephropathy.

Application

Q: A 60-year-old man has 6 g/day proteinuria, low albumin, oedema, and positive anti-PLA2R antibodies. What is the likely diagnosis and one important secondary workup? A: Primary membranous nephropathy (anti-PLA2R is fairly specific). Because membranous can be paraneoplastic, pursue age-appropriate malignancy screening; also check hepatitis B serology.

Analysis

Q: A 70-year-old has rising creatinine over two weeks, active urine sediment, hemoptysis, and positive MPO-ANCA. Complement is normal. What syndrome and biopsy pattern do you expect, and why is speed essential? A: ANCA-associated pauci-immune rapidly progressive glomerulonephritis; expect crescents on light microscopy with scant immunofluorescence. Speed matters because crescentic injury destroys nephrons within days — early immunosuppression (and plasma exchange in severe/overlap cases) preserves kidney function.

FAQ

Is nephrotic syndrome the same as nephritic syndrome? No. Nephrotic is a leaky filter (heavy protein, low albumin, oedema, bland urine); nephritic is an inflamed filter (blood, red-cell casts, hypertension, falling function). Some diseases cause a mixed picture, which is one reason biopsy is often needed.

Does every patient with glomerular disease need a biopsy? No. Children with a classic steroid-responsive nephrotic presentation and long-standing diabetics with a typical course are often treated empirically. Biopsy is reserved for uncertain, atypical, rapidly progressive, or treatment-resistant cases — but for most adults it is decisive.

Is a renal biopsy dangerous? It is a common, generally safe procedure done under ultrasound guidance. The main risk is bleeding; patients are screened for coagulation problems and uncontrolled hypertension beforehand and observed afterward. Serious complications are uncommon.

Can glomerular diseases be cured? Some are self-limiting (post-streptococcal GN in children usually resolves). Others (minimal change disease) often remit fully with steroids. Many (IgA nephropathy, membranous, diabetic nephropathy) are managed to slow progression rather than cured. Outcome depends heavily on the specific diagnosis and how much scarring already exists.

Why do doctors keep measuring my urine protein instead of just my creatinine? Because proteinuria rises early — often years before creatinine changes — and its level predicts how fast the kidney will decline and how well it responds to treatment. Reducing proteinuria is itself a therapeutic goal.

Quick Revision

• Nephrotic = protein (more than 3.5 g/day) + low albumin + oedema + lipids; bland urine.
• Nephritic = hematuria + red-cell casts + hypertension + falling GFR.
• Richard Bright (1827) linked albuminuria, dropsy, and diseased kidneys — "Bright's disease."
• Commonest childhood nephrotic cause: minimal change disease (steroid-responsive).
• Commonest primary GN worldwide: IgA nephropathy (synpharyngitic hematuria).
• Post-streptococcal GN: 1–3 week latency, low C3, self-limiting.
• RPGN = crescents; three types by IF — linear (anti-GBM), granular (immune complex), pauci-immune (ANCA).
• Biopsy = light microscopy + immunofluorescence + electron microscopy.
• Anti-PLA2R points to primary membranous; low C3+C4 to lupus/cryo.

Related Topics

Prerequisites

• Nephrology overview
• Renal physiology and glomerular filtration (see ../../2._Physiology/index.md)

Related Topics

• Acute kidney injury and chronic kidney disease (within Nephrology)
• Immunology and the complement cascade (see ../../34._Immunology/index.md)
• Pathology of the kidney (see ../../4._Pathology/index.md)

Next Topics

• Management of nephrotic syndrome and immunosuppression
• Dialysis and renal replacement therapy