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.

Minimal change disease is characterised as a cause of nephrotic syndrome without visible changes in the glomerulus on microscopy. Minimal change disease typically presents with edema, an increase in proteins passed from urine and decrease in blood protein levels, and an increase in circulating lipids (i.e., nephrotic syndrome) and is the most common cause of the nephrotic syndrome in children. Although no changes may be visible by light microscopy, changes on electron microscopy within the glomerules may show a fusion of the foot processes of the podocytes (cells lining the basement membrane of the capillaries of glomerulus). It is typically managed with corticosteroids and does not progress to chronic kidney disease.

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.

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.

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.

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.)

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.

Histologically, IgA nephropathy may show mesangial widening and focal and segmental inflammation. Diffuse mesangial proliferation or crescentic glomerulonephritis may also be present. Immunoflourescence shows mesangial deposition of IgA often with C3 and properdin and smaller amounts of other immunoglobulins (IgG or IgM). Early components of the classical complement pathway (C1q or C4) are usually not seen. Electron microscopy confirms electron-dense deposits in the mesangium that may extend to the subendothelial area of adjacent capillary walls in a small subset of cases, usually those with focal proliferation.

Some general secondary causes are listed below:

- Glomerular hypertrophy/hyperfiltration

- Unilateral renal agenesis

- Morbid obesity

- Scarring due to previous injury

- Focal proliferative glomerulonephritis

- Vasculitis

- Lupus

- Toxins (pamidronate)

- Human immunodeficiency virus-associated nephropathy

- Heroin nephropathy

Focal segmental glomerulosclerosis may develop following acquired loss of nephrons from reflux nephropathy. Proteinuria is nonselective in most cases and may be in subnephrotic range (nephritic range <3.0gm/24hr) or nephritic range.

In children and some adults, FSGS presents as a nephrotic syndrome, which is characterized by edema (associated with weight gain), hypoalbuminemia (low serum albumin, a protein in the blood), hyperlipidemia and hypertension (high blood pressure). In adults, it may also present as kidney failure and proteinuria, without a full-blown nephrotic syndrome.

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

- Hematuria:

- Oliguria

- Edema

- Hypertension

- Fever, headache, malaise, anorexia, nausea.

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.

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.

Primary causes of nephrotic syndrome are usually described by their histology:

- Minimal change disease (MCD): is the most common cause of nephrotic syndrome in children. It owes its name to the fact that the nephrons appear normal when viewed with an optical microscope as the lesions are only visible using an electron microscope. Another symptom is a pronounced proteinuria.

- Focal segmental glomerulosclerosis (FSGS): is the most common cause of nephrotic syndrome in adults. It is characterized by the appearance of tissue scarring in the glomeruli. The term "focal" is used as some of the glomeruli have scars, while others appear intact; the term "segmental" refers to the fact that only part of the glomerulus suffers the damage.

- Membranous glomerulonephritis (MGN): The inflammation of the glomerular membrane causes increased leaking in the kidney. It is not clear why this condition develops in most people, although an auto-immune mechanism is suspected.

- Membranoproliferative glomerulonephritis (MPGN): is the inflammation of the glomeruli along with the deposit of antibodies in their membranes, which makes filtration difficult.

- Rapidly progressive glomerulonephritis (RPGN): (Usually presents as a nephritic syndrome) A patient’s glomeruli are present in a "crescent moon" shape. It is characterized clinically by a rapid decrease in the glomerular filtration rate (GFR) by at least 50% over a short period, usually from a few days to 3 months.

They are considered to be "diagnoses of exclusion", i.e. they are diagnosed only after secondary causes have been excluded.

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.

Nephrosis is any of various forms of kidney disease (nephropathy). In an old and broad sense of the term, it is any nephropathy, but in current usage the term is usually restricted to a narrower sense of nephropathy without inflammation or neoplasia, in which sense it is distinguished from nephritis, which involves inflammation. It is also defined as any purely degenerative disease of the renal tubules. Nephrosis is characterized by a set of signs called the nephrotic syndrome. Nephrosis can be a primary disorder or can be secondary to another disorder. Nephrotic complications of another disorder can coexist with nephritic complications. In other words, nephrosis and nephritis can be pathophysiologically contradistinguished, but that does not mean that they cannot occur simultaneously.

Types of nephrosis include amyloid nephrosis and osmotic nephrosis.

The prognosis for nephrotic syndrome under treatment is generally good although this depends on the underlying cause, the age of the patient and their response to treatment. It is usually good in children, because minimal change disease responds very well to steroids and does not cause chronic renal failure. Any relapses that occur become less frequent over time; the opposite occurs with mesangiocapillary glomerulonephritis, in which the kidney fails within three years of the disease developing, making dialysis necessary and subsequent kidney transplant. In addition children under the age of 5 generally have a poorer prognosis than prepubescents, as do adults older than 30 years of age as they have a greater risk of kidney failure.

Other causes such as focal segmental glomerulosclerosis frequently lead to end stage renal disease. Factors associated with a poorer prognosis in these cases include level of proteinuria, blood pressure control and kidney function (GFR).

Without treatment nephrotic syndrome has a very bad prognosis especially "rapidly progressing glomerulonephritis", which leads to acute kidney failure after a few months.

The differential diagnosis of acute proliferative glomerulonephritisis is based on the following:

Transplant glomerulopathy, abbreviated TG, is a disease of the glomeruli in transplanted kidneys. It is a type of renal injury often associated with chronic antibody-mediated rejection. However, transplant glomerulopathy is not specific for chronic antibody-mediated rejection; it may be the result of a number of disease processes affecting the glomerular endothelium.

The diagnosis of lupus nephritis depends on blood tests, urinalysis, X-rays, ultrasound scans of the kidneys, and a kidney biopsy. On urinalysis, a nephritic picture is found and red blood cell casts, red blood cells and proteinuria is found. The World Health Organization has divided lupus nephritis into five stages based on the biopsy. This classification was defined in 1982 and revised in 1995.

- Class I is minimal mesangial glomerulonephritis which is histologically normal on light microscopy but with mesangial deposits on electron microscopy. It constitutes about 5% of cases of lupus nephritis. Kidney failure is very rare in this form.

- Class II is based on a finding of mesangial proliferative lupus nephritis. This form typically responds completely to treatment with corticosteroids. It constitutes about 20% of cases. Kidney failure is rare in this form.

- Class III is focal proliferative nephritis and often successfully responds to treatment with high doses of corticosteroids. It constitutes about 25% of cases. Kidney failure is uncommon in this form.

- Class IV is diffuse proliferative nephritis. This form is mainly treated with corticosteroids and immunosuppressant drugs. It constitutes about 40% of cases. Kidney failure is common in this form.

- Class V is membranous nephritis and is characterized by extreme edema and protein loss. It constitutes about 10% of cases. Kidney failure is uncommon in this form.

Proteinuria is the presence of excess proteins in the urine. In healthy persons, urine contains very little protein; an excess is suggestive of illness. Excess protein in the urine often causes the urine to become foamy, although foamy urine may also be caused by bilirubin in the urine (bilirubinuria), retrograde ejaculation, pneumaturia (air bubbles in the urine) due to a fistula, or drugs such as pyridium.

Glomerulonephrosis is a non-inflammatory disease of the kidney (nephrosis) presenting primarily in the glomerulus (a glomerulopathy).

It can be contrasted to glomerulonephritis, which implies inflammation.

It can be caused by diethylnitrosamine.

The clinical signs of minimal change disease are proteinuria (abnormal excretion of proteins, mainly albumin, into the urine), oedema (swelling of soft tissues as a consequence of water retention), and hypoalbuminaemia (low serum albumin). These signs are referred to collectively as nephrotic syndrome. Minimal change disease is unique among the causes of nephrotic syndrome as it lacks evidence of pathology in light microscopy, hence the name.

When albumin is excreted in the urine, its serum (blood) concentration decreases. Consequently, the intravascular oncotic pressure reduces relative to the interstitial tissue. The subsequent movement of fluid from the vascular compartment to the interstitial compartment manifests as the soft tissue swelling referred to as oedema. This fluid collects most commonly in the feet and legs, in response to gravity, particularly in those with poorly functioning valves. In severe cases, fluid can shift into the peritoneal cavity (abdomen) and cause ascites. As a result of the excess fluid, individuals with minimal change disease often gain weight, as they are excreting less water in the urine, and experience fatigue. Additionally, the protein in the urine causes it to become frothy.

There are three main mechanisms to cause proteinuria:

- Due to disease in the glomerulus

- Because of increased quantity of proteins in serum (overflow proteinuria)

- Due to low reabsorption at proximal tubule (Fanconi syndrome)

Proteinuria can also be caused by certain biological agents, such as bevacizumab (Avastin) used in cancer treatment. Excessive fluid intake (drinking in excess of 4 litres of water per day) is another cause.

Also leptin administration to normotensive Sprague Dawley rats during pregnancy significantly increases urinary protein excretion.

Proteinuria may be a sign of renal (kidney) damage. Since serum proteins are readily reabsorbed from urine, the presence of excess protein indicates either an insufficiency of absorption or impaired filtration. People with diabetes may have damaged nephrons and develop proteinuria. The most common cause of proteinuria is diabetes, and in any person with proteinuria and diabetes, the cause of the underlying proteinuria should be separated into two categories: diabetic proteinuria versus the field.

With severe proteinuria, general hypoproteinemia can develop which results in

diminished oncotic pressure. Symptoms of diminished oncotic pressure may include ascites, edema and hydrothorax.