IgA nephropathy, also known as "Berger's disease", is the most common type of glomerulonephritis, and generally presents with isolated visible or occult hematuria, occasionally combined with low grade proteinuria, and rarely causes a nephritic syndrome characterised by protein in the urine, and visible blood in the urine. IgA nephropathy is classically described as a self-resolving form in young adults several days after a respiratory infection. It is characterised by deposits of IgA in the space between glomerular capillaries.

Henoch–Schönlein purpura refers to a form of IgA nephropathy, typically affecting children, characterised by a rash of small bruises affecting the buttocks and lower legs, with abdominal pain.

Post-infectious glomerulonephritis can occur after essentially any infection, but classically occurs after infection with the bacteria "Streptococcus pyogenes". It typically occurs 1–4 weeks after a pharyngeal infection with this bacterium, and is likely to present with malaise, a slight fever, nausea and a mild nephritic syndrome of moderately increased blood pressure, gross haematuria, and smoky-brown urine. Circulating immune complexes that deposit in the glomerules may lead to an inflammatory reaction.

Diagnosis may be made on clinical findings or through antistreptolysin O antibodies found in the blood. A biopsy is seldom done, and the disease is likely to self-resolve in children in 1–4 weeks, with a poorer prognosis if adults are affected.

Clinical features may include constitutional symptoms like fever, loss of appetite, weight loss, fatigue, and kidney failure. A majority of patients may have blood in the urine and protein in the urine. Rapidly progressive glomerulonephritis may occur. Because many different organ systems may be involved, a wide range of symptoms are possible in MPA.

Purpura and livedo racemosa may be present.

The classic presentation (in 40–50% of the cases) is episodic hematuria, which usually starts within a day or two of a non-specific upper respiratory tract infection (hence "synpharyngitic"), as opposed to post-streptococcal glomerulonephritis, which occurs some time (weeks) after initial infection. Less commonly gastrointestinal or urinary infection can be the inciting agent. All of these infections have in common the activation of mucosal defenses and hence IgA antibody production. Groin pain can also occur. The gross hematuria resolves after a few days, though microscopic hematuria may persist. These episodes occur on an irregular basis every few months and in most patients eventually subsides, although it can take many years. Renal function usually remains normal, though rarely, acute kidney failure may occur (see below). This presentation is more common in younger adults.

A smaller proportion (20-30%), usually the older population, have microscopic hematuria and proteinuria (less than 2 gram/day). These patients may not have any symptoms and are only clinically found if a physician decides to take a urine sample. Hence, the disease is more commonly diagnosed in situations where screening of urine is compulsory (e.g., schoolchildren in Japan).

Very rarely (5% each), the presenting history is:

- Nephrotic syndrome (3-3.5 grams of protein loss in the urine, associated with a poorer prognosis)

- Acute kidney failure (either as a complication of the frank hematuria, when it usually recovers, or due to rapidly progressive glomerulonephritis which often leads to chronic kidney failure)

- Chronic kidney failure (no previous symptoms, presents with anemia, hypertension and other symptoms of kidney failure, in people who probably had longstanding undetected microscopic hematuria and/or proteinuria)

A variety of systemic diseases are associated with IgA nephropathy such as liver failure, celiac disease, rheumatoid arthritis, reactive arthritis, ankylosing spondylitis and HIV. Diagnosis of IgA nephropathy and a search for any associated disease occasionally reveals such an underlying serious systemic disease. Occasionally, there are simultaneous symptoms of Henoch–Schönlein purpura; see below for more details on the association. Some HLA alleles have been suspected along with complement phenotypes as being genetic factors.

Class I disease (minimal mesangial glomerulonephritis) in its histology has a normal appearance under a light microscope, but mesangial deposits are visible under an electron microscope. At this stage urinalysis is normal.

Class II disease (mesangial proliferative glomerulonephritis) is noted by mesangial hypercellularity and matrix expansion. Microscopic haematuria with or without proteinuria may be seen. Hypertension, nephrotic syndrome, and acute kidney insufficiency are very rare at this stage.

Class III disease (focal glomerulonephritis) is indicated by sclerotic lesions involving less than 50% of the glomeruli, which can be segmental or global, and active or chronic, with endocapillary or extracapillary proliferative lesions. Under the electron microscopy, subendothelial deposits are noted, and some mesangial changes may be present. Immunofluorescence reveals positively for IgG, IgA, IgM, C3, and C1q. Clinically, haematuria and proteinuria are present, with or without nephrotic syndrome, hypertension, and elevated serum creatinine.

Class IV disease (diffuse proliferative nephritis) is both the most severe, and the most common subtype. More than 50% of glomeruli are involved. Lesions can be segmental or global, and active or chronic, with endocapillary or extracapillary proliferative lesions. Under electron microscopy, subendothelial deposits are noted, and some mesangial changes may be present. Clinically, haematuria and proteinuria are present, frequently with nephrotic syndrome, hypertension, hypocomplementemia, elevated anti-dsDNA titres and elevated serum creatinine.

Class V disease (membranous glomerulonephritis) is characterized by diffuse thickening of the glomerular capillary wall (segmentally or globally), with diffuse membrane thickening, and subepithelial deposits seen under the electron microscope. Clinically, stage V presents with signs of nephrotic syndrome. Microscopic haematuria and hypertension may also been seen. Stage V also can also lead to thrombotic complications such as renal vein thromboses or pulmonary emboli.

A final Class is included by most practitioners, Class VI, or advanced sclerosing lupus nephritis. It is represented by global sclerosis involving more than 90% of glomeruli, and represents healing of prior inflammatory injury. Active glomerulonephritis is not usually present. This stage is characterised by slowly progressive kidney dysfunction, with relatively bland urine sediment. Response to immunotherapy is usually poor. A tubuloreticular inclusion within capillary endothelial cells is also characteristic of lupus nephritis, and can be seen under an electron microscope in all stages. It is not diagnostic however, as it exists in other conditions such as HIV infection. It is thought to be due to the chronic interferon exposure.

Microscopic polyangiitis is an ill-defined autoimmune disease characterized by a systemic, pauci-immune, necrotizing, small-vessel vasculitis without clinical or pathological evidence of necrotizing granulomatous inflammation.

Lupus nephritis (also known as SLE nephritis) is an inflammation of the kidneys caused by systemic lupus erythematosus (SLE), an autoimmune disease. It is a type of glomerulonephritis in which the glomeruli become inflamed. As the result of SLE, the cause of glomerulonephritis is said to be "secondary" and has a different pattern and outcome from conditions with a "primary" cause originating in the kidney.

Some people may present as nephrotic syndrome with proteinuria, edema with or without renal failure. Others may be asymptomatic and may be picked up on screening or urinalysis as having proteinuria. A definitive diagnosis of membranous nephropathy requires a kidney biopsy.

Among the signs and symptoms of acute proliferative glomerulonephritis are the following:

- Hematuria:

- Oliguria

- Edema

- Hypertension

- Fever, headache, malaise, anorexia, nausea.

IgA nephropathy (IgAN), also known as IgA nephritis, Berger disease () (and variations), or synpharyngitic glomerulonephritis, is a disease of the kidney (or nephropathy); specifically it is a form of glomerulonephritis or an inflammation of the glomeruli of the kidney.

IgA nephropathy is the most common glomerulonephritis worldwide. Primary IgA nephropathy is characterized by deposition of the IgA antibody in the glomerulus. There are other diseases associated with glomerular IgA deposits, the most common being IgA vasculitis (formerly known as Henoch–Schönlein purpura [HSP]), which is considered by many to be a systemic form of IgA nephropathy. IgA vasculitis presents with a characteristic purpuric skin rash, arthritis, and abdominal pain and occurs more commonly in young adults (16–35 years old). HSP is associated with a more benign prognosis than IgA nephropathy. In IgA nephropathy there is a slow progression to chronic kidney failure in 25–30% of cases during a period of 20 years.

The closely related terms membranous nephropathy and membranous glomerulopathy both refer to a similar constellation but without the assumption of inflammation.

Membranous nephritis (in which inflammation is implied, but the glomerulus not explicitly mentioned) is less common, but the phrase is occasionally encountered. These conditions are usually considered together.

By contrast, membranoproliferative glomerulonephritis has a similar name, but is considered a separate condition with a distinctly different causality. Membranoproliferative glomerulonephritis involves the basement membrane and mesangium, while membranous glomerulonephritis involves the basement membrane but not the mesangium. (Membranoproliferative glomerulonephritis has the alternate name "mesangiocapillary hohki", to emphasize its mesangial character.)

Mesangial proliferative glomerulonephritis is a form of glomerulonephritis associated primarily with the mesangium. There is some evidence that interleukin-10 may inhibit it in an animal model. It is classified as type II lupus nephritis by the World Health Organization (WHO).

Hypersensitivity vasculitis (allergic vasculitis). Usually due to a hypersensitivity reaction to a known drug. Drugs most commonly implicated are penicillin, sulphonamides and thiazide diuretics. There is presence of skin vaculitis with palpable petechiae or purpura. Biopsy of these lesions reveal inflammation of the small vessels, termed leukocytoclastic vasculitis, which is most prominent in postcapillary venules. At least 3 out of 5 criteria yields sensitivity and specificity of 71 and 84%:

- age > 16

- use of possible triggering drug in relation to symptoms

- palpable purpura

- maculopapular rash

- skin biopsy showing neutrophils around vessel

IgA vasculitis (IgAV; formerly known as Henoch-Schonlein purpura). Systemic vasculitis due to tissue deposition of IgA-containing immune complexes. Biopsy of lesions shows inflammation of small vessels. It is considered a form of hypersensitivity vasculitis but is distinguished by prominent deposits of IgA. This is the most common vasculitis in children. Presence of 3 or more criteria yielded sensitivity of 87% while less than 2 criteria yielded hypersensitivity vasculitis in 74%:

- palpable purpura (usually of buttocks & legs)

- bowel angina

- GI bleed

- hematuria

- onset < 20 years

- no new medications

Essential cryoglobulinemic vasculitis. Most often due to hepatitis C infection, immune complexes of cryoglobulins --- proteins that consists of immunoglobulins and complement and precipitate in the cold while dissolving upon rewarming --- are deposited in walls of capillaries, venules, or arterioles. Therefore, complement will be low with histology showing vessel inflammation with immune deposits.

There are three types of MPGN, but this classification is becoming obsolete as the causes of this pattern are becoming understood.

The GBM is rebuilt on top of the deposits, causing a "tram tracking" appearance under the microscope. Mesangial cellularity is increased.

Patients usually present with systemic symptoms with single or multiorgan dysfunction. Common (and nonspecific) complaints include fatigue, weakness, fever, arthralgias, abdominal pain, hypertension, renal insufficiency, and neurologic dysfunction. The following symptoms should raise a strong suspicion of a vasculitis:

- Mononeuritis multiplex. Also known as asymmetric polyneuropathy, in a non-diabetic this is suggestive of vasculitis.

- Palpable purpura. If patients have this in isolation, it is most likely due to cutaneous leukocytoclastic vasculitis. If the purpura is in combination with systemic organ involvement, it is most likely to be Henoch-Schonlein purpura or microscopic polyarteritis.

- Pulmonary-renal syndrome. Individuals who are coughing up blood and have kidney involvement are likely to have granulomatosis with polyangiitis, microscopic polyangiitis, or anti-GBM disease (Goodpasture's syndrome).

Most types of RPGN are characterized by severe and rapid loss of kidney function featuring severe hematuria (blood in the urine), red blood cell casts in the urine, and proteinuria (protein in the urine), sometimes exceeding 3 g protein/24 h, a range associated with nephrotic syndrome. Some patients also experience hypertension (high blood pressure) and edema. Severe disease is characterized by pronounced oliguria or anuria, which portends a poor prognosis.

RPGN caused by the deposition of immune complexes accounts for 25% of RPGN and is classified as type II. Thus any immune complex disease that involves the glomerulus may progress to RPGN if severe enough. These diseases include systemic lupus erythematosus, acute proliferative glomerulonephritis, Henoch–Schönlein purpura and IgA nephropathy.

Pauci-immune (pauci- Latin: few, little) vasculitis is a form of vasculitis that is associated with minimal evidence of hypersensitivity upon immunofluorescent staining for IgG.

Normally a kidney sample will be subjected to immunofluorescence if rapidly progressive glomerulonephritis is a concern. In this case, the immunofluorescence can show three patterns: linear, granular and negative (pauci-immune). The linear and granular patterns are examples of positive immunofluorescence and are associated with Goodpasture syndrome and post-streptococcal glomerulonephritis accordingly. A negative pattern or pauci-immune pattern can be associated with systemic vasculitis such as microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis (EGPA) or granulomatosis with polyangiitis (GPA). In many cases however, it is limited to the kidney and it is thus called idiopathic.

Since it can be associated with the three systemic vasculitides mentioned above, a pauci-immune pattern finding can be associated with antineutrophil cytoplasmic antibodies (ANCA). Therefore, an ANCA test should follow a negative immunofluorescence result in order to distinguish between the above-mentioned systemic vasculitis.

Peak incidences in 50- to 60-year-olds symptoms include intermittent fever / weight loss / shortness of breath / joint pain.

The prodromal stage is characterized by allergy. Almost all patients experience asthma and/or allergic rhinitis, with more than 90% having a history of asthma that is either a new development, or the worsening of pre-existing asthma, which may require systemic corticosteroid treatment. On average, asthma develops from three to nine years before the other signs and symptoms.

The allergic rhinitis may produce symptoms such as rhinorrhea and nasal obstruction, and the formation of nasal polyps that require surgical removal, often more than once. Sinusitis may also be present.

The second stage is characterized by an abnormally high level of eosinophils (a type of white blood cell) in the blood and tissues. The symptoms of hypereosinophilia depend on which part of the body is affected, but most often it affects the lungs and digestive tract. The signs and symptoms of hypereosinophilia may include weight loss, night sweats, asthma, cough, abdominal pain, and gastrointestinal bleeding. Fever and malaise are often present.

The eosinophilic stage can last months or years, and its symptoms can disappear, only to return later. Patients may experience the third stage simultaneously.

Initial signs are extremely variable, and diagnosis can be severely delayed due to the nonspecific nature of the symptoms. In general, rhinitis is the first sign in most people.

- Kidney: rapidly progressive glomerulonephritis (75%), leading to chronic kidney failure

- Upper airway, eye and ear disease:

- Nose: pain, stuffiness, nosebleeds, rhinitis, crusting, "saddle-nose" deformity due to a perforated septum

- Ears: conductive hearing loss due to auditory tube dysfunction, sensorineural hearing loss (unclear mechanism)

- Oral cavity: strawberry gingivitis, underlying bone destruction with loosening of teeth, non-specific ulcerations throughout oral mucosa

- Eyes: pseudotumours, scleritis, conjunctivitis, uveitis, episcleritis

- Trachea: subglottal stenosis

- Lungs: pulmonary nodules (referred to as "coin lesions"), infiltrates (often interpreted as pneumonia), cavitary lesions, pulmonary haemorrhage causing haemoptysis, and rarely bronchial stenosis.

- Arthritis: Pain or swelling (60%), often initially diagnosed as rheumatoid arthritis

- Skin: nodules on the elbow, purpura, various others (see "cutaneous vasculitis")

- Nervous system: occasionally sensory neuropathy (10%) and rarely mononeuritis multiplex

- Heart, gastrointestinal tract, brain, other organs: rarely affected.

Acute proliferative glomerulonephritis is a disorder of the glomeruli (glomerulonephritis), or small blood vessels in the kidneys. It is a common complication of bacterial infections, typically skin infection by "Streptococcus" bacteria types 12, 4 and 1 (impetigo) but also after streptococcal pharyngitis, for which it is also known as "postinfectious" or poststreptococcal glomerulonephritis. It can be a risk factor for future albuminuria. In adults, the signs and symptoms of infection may still be present at the time when the kidney problems develop, and the terms infection-related glomerulonephritis or bacterial infection-related glomerulonephritis are also used. Acute glomerulonephritis resulted in 19,000 deaths in 2013 down from 24,000 deaths in 1990 worldwide.

It is characterized by glomerular basement membrane thickening (referred to as "tram-tracking of the basement membrane"), increased mesangial matrix and segmental and global glomerulosclerosis.

The differential diagnosis of tram-tracking includes membranoproliferative glomerulonephritis (especially hepatitis C), and thrombotic microangiopathies.

Diffuse proliferative nephritis (DPN) or glomerulonephritis (DPGN) is a type of glomerulonephritis that is the most serious form of renal lesions in SLE and is also the most common, occurring in 35% to 60% of patients. Most of the glomeruli show endothelial and mesangial proliferation affecting the entire glomerulus, leading to diffuse hypercellularity of the glomeruli, producing in some cases epithelial crescents that fill Bowman's space. When extensive, immune complexes create an overall thickening of the capillary wall, resembling rigid "wire loops" on routine light microscopy. Electron microscopy reveals electron-dense subendothelial immune complexes (between endothelium and basement membrane). Immune complexes can be visualized by staining with fluorescent antibodies directed against immunoglobulins or complement, resulting in a granular fluorescent staining pattern. In due course, glomerular injury gives rise to scarring (glomerulosclerosis). Most of these patients have hematuria with moderate to severe proteinuria, hypertension, and renal insufficiency.