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.

The treatment of nephrotic syndrome can be symptomatic or can directly address the injuries caused to the kidney.

Proteinuria may be a feature of the following conditions:

- Nephrotic syndromes (i.e. intrinsic renal failure)

- Pre-eclampsia

- Eclampsia

- Toxic lesions of kidneys

- Amyloidosis

- Collagen vascular diseases (e.g. systemic lupus erythematosus)

- Dehydration

- Glomerular diseases, such as membranous glomerulonephritis, focal segmental glomerulonephritis, minimal change disease (lipoid nephrosis)

- Strenuous exercise

- Stress

- Benign orthostatic (postural) proteinuria

- Focal segmental glomerulosclerosis (FSGS)

- IgA nephropathy (i.e. Berger's disease)

- IgM nephropathy

- Membranoproliferative glomerulonephritis

- Membranous nephropathy

- Minimal change disease

- Sarcoidosis

- Alport's syndrome

- Diabetes mellitus (diabetic nephropathy)

- Drugs (e.g. NSAIDs, nicotine, penicillamine, lithium carbonate, gold and other heavy metals, ACE inhibitors, antibiotics, or opiates (especially heroin)

- Fabry's disease

- Infections (e.g. HIV, syphilis, hepatitis, poststreptococcal infection, urinary schistosomiasis)

- Aminoaciduria

- Fanconi syndrome in association with Wilson disease

- Hypertensive nephrosclerosis

- Interstitial nephritis

- Sickle cell disease

- Hemoglobinuria

- Multiple myeloma

- Myoglobinuria

- Organ rejection:

- Ebola virus disease

- Nail patella syndrome

- Familial Mediterranean fever

- HELLP Syndrome

- Systemic lupus erythematosus

- Granulomatosis with polyangiitis

- Rheumatoid arthritis

- Glycogen storage disease type 1

- Goodpasture's syndrome

- Henoch–Schönlein purpura

- A urinary tract infection which has spread to the kidney(s)

- Sjögren's syndrome

- Post-infectious glomerulonephritis

Nephrotic syndrome can affect any age, although it is mainly found in adults with a ratio of adults to children of 26 to 1.

The syndrome presents in different ways in the two groups: the most frequent glomerulopathy in children is minimal change disease (66% of cases), followed by focal segmental glomerulosclerosis (8%) and mesangiocapillary glomerulonephritis (6%). In adults the most common disease is mesangiocapillary glomerulonephritis (30-40%), followed by focal and segmental glomeruloesclerosis (15-25%) and minimal change disease (20%). The latter usually presents as secondary and not primary as occurs in children. Its main cause is diabetic nephropathy. It usually presents in a patient’s 40s or 50s.

Of the glomerulonephritis cases approximately 60% to 80% are primary, while the remainder are secondary.

There are also differences in epidemiology between the sexes, the disease is more common in men than in women by a ratio of 2 to 1.

The epidemiological data also reveals information regarding the most common way that symptoms develop in patients with nephrotic syndrome: spontaneous remission occurs in up to 20% or 30% of cases during the first year of the illness. However, this improvement is not definitive as some 50% to 60% of patients die and / or develop chronic renal failure 6 to 14 years after this remission. On the other hand, between 10% and 20% of patients have continuous episodes of remissions and relapses without dying or jeopardizing their kidney. The main causes of death are cardiovascular, as a result of the chronicity of the syndrome, and thromboembolic accidents.

The kidneys normally do not filter large molecules into the urine, so albuminuria can be an indicator of damage to the kidneys or excessive salt intake. It can also occur in patients with long-standing diabetes, especially type 1 diabetes. Recent international guidelines (KDIGO 2012) reclassified chronic kidney disease (CKD) based on cause, glomerular filtration rate category, and albuminuria category (A1, A2, A3).

Causes of albuminuria can be discriminated between by the amount of protein excreted.

- The nephrotic syndrome usually results in the excretion of about 3.0 to 3.5 grams per 24 hours.

- Nephritic syndrome results in far less albuminuria.

- Microalbuminuria (between 30 and 300 mg/24h, mg/l of urine or µg/mg of creatinine) can be a forerunner of diabetic nephropathy. The term albuminuria is now preferred in Nephrology since there is not a "small albumin" ("micro"albuminuria) or a "big albumin" ("macro"albuminuria). A1 represents normal to mildly increased urinary albumin/creatinine ratio (300 mg/g or > 30 mg/mmol).

Orthostatic proteinuria (synonyms: orthostatic albuminuria, postural proteinuria) is a benign condition. A change in renal hemodynamics, which in some otherwise normal individuals, causes protein (mostly albumin) to appear in urine when they are in the standing position. Urine formed when these individuals are lying down is protein-free.

There is normal urinary protein excretion during the night but increased excretion during the day, associated with activity and upright posture. Total urinary protein excretion may be increased but levels above 1 g per 24 hours are more likely to be associated with underlying renal disease. The exact cause of orthostatic proteinuria is not known.

Though there is some evidence that dietary interventions (to lower red meat intake) can be helpful in lowering albuminuria levels, there is currently no evidence that low protein interventions correlate to improvement in kidney function. Among other measures, blood pressure control, especially with the use of inhibitors of the renin-angiotensin-system, is the most commonly used therapy to control albuminuria.

According to the United States Renal Data System (USRDS), hypertensive nephropathy accounts for more than one-third of patients on hemodialysis and the annual mortality rate for patients on hemodialysis is 23.3%.

Haemodialysis is recommended for patients who progress to end-stage kidney disease (ESKD) and hypertensive nephropathy is the second most common cause of ESKD after diabetes.

Patient prognosis is dependent on numerous factors including age, ethnicity, blood pressure and glomerular filtration rate. Changes in lifestyle factors, such as reduced salt intake and increased physical activity have been shown to improve outcomes but are insufficient without pharmacological treatment.

More specifically, glomerulosclerosis can refer to:

- Focal segmental glomerulosclerosis

- Nodular glomerulosclerosis (diabetic)

The incidence of hypertensive nephropathy varies around the world. For instance, it accounts for as many as 25% and 17% of patients starting dialysis for end-stage kidney disease in Italy and France respectively. Contrastingly, Japan and China report only 6 and 7% respectively. Since the year 2000, nephropathy caused by hypertension has increased in incidence by 8.7% In reality, these figures may be even higher, as hypertension is not always reported as the specific cause of kidney disease.

It has been recognized that the incidence of hypertensive nephropathy varies with ethnicity. Compared to Caucasians, African Americans in the USA are much more likely to develop hypertensive nephropathy. Of those who do, the proportion who then go on to develop end-stage renal failure is 3.5 times higher than in the Caucasian population. In addition to this, African Americans tend to develop hypertensive nephropathy at a younger age than Caucasians (45 to 65, compared to >65).

Diabetic nephropathy in type 2 diabetes can be more difficult to predict because the onset of diabetes is not usually well established. Without intervention, 20-40 percent of patients with type 2 diabetes/microalbuminuria, will evolve to macroalbuminuria.

Diabetic nephropathy is the most common cause of end-stage kidney disease, which may require hemodialysis or even kidney transplantation. It is associated with an increased risk of death in general, particularly from cardiovascular disease.

The incidence of diabetic nephropathy is higher in diabetics with one or more of the following conditions:

- Poor control of blood glucose

- Uncontrolled High blood pressure

- Type 1 diabetes mellitus, with onset before age 20

- Past or current cigarette use

- A family history of diabetic nephropathy

Inflammation of or injury to the glomeruli can cause leakage of red blood cells, resulting in misshapen cells and red blood cell casts in the urine. Glomerular bleeding is frequently accompanied by proteinuria, or leakage of protein into the urine.

Common causes include

- IgA nephropathy

- Hereditary nephritis (Alport's disease)

- Benign familiar hematuria

- Glomerulonephritis–a group of inflammatory diseases of the glomeruli, leading to hematuria, hypertension, and peripheral edema

Management of sickle nephropathy is not separate from that of overall patient management. In addition, however, the use of ACE inhibitors has been associated with improvement of the hyperfiltration glomerulopathy. Three-year graft and patient survival in kidney transplant recipients with sickle nephropathy is lower when compared to those with other causes of end-stage kidney disease.

In many cases of asymptomatic microscopic hematuria without proteinuria, no etiology is found. Common causes of microscopic hematuria in pediatric populations include:

- hypercalciuria–suspected in a child with family history of kidney stones; can be asymptomatic or can cause painful urination

- benign familial hematuria–a genetic disorder causing persistent microscopic hematuria

- IgA nephropathy

- sickle cell trait or disease

- Alport syndrome–a genetic disorder causing recurrent microscopic hematuria with proteinuria, hearing loss, and progressive kidney failure

The epidemiology of rapidly progressive glomerulonephritis according to Hedger, et al., is an incidence rate of 3.9 individuals per million (3.3–4.7) with a 95% confidence intervals.

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.

Male gender, proteinuria (especially > 2 g/day), hypertension, smoking, hyperlipidemia, older age, familial disease and elevated creatinine concentrations are markers of a poor outcome. Frank hematuria has shown discordant results with most studies showing a better prognosis, perhaps related to the early diagnosis, except for one group which reported a poorer prognosis. Proteinuria and hypertension are the most powerful prognostic factors in this group.

There are certain other features on kidney biopsy such as interstitial scarring which are associated with a poor prognosis. ACE gene polymorphism has been recently shown to have an impact with the DD genotype associated more commonly with progression to kidney failure.

Overall, most people with thin basement membrane disease have an excellent prognosis. Some reports, however, suggest that a minority might develop hypertension.

Thin basement membrane disease may co-exist with other kidney diseases, which may in part be explained by the high prevalence of thin basement membrane disease.

Glomerulosclerosis, also known as glomerular sclerosis, refers to a hardening of the glomerulus in the kidney. It is a general term to describe scarring of the kidneys' tiny blood vessels, the glomeruli, the functional units in the kidney that filter urine from the blood.

Proteinuria (large amounts of protein in urine) is one of the signs of glomerulosclerosis. Scarring disturbs the filtering process of the kidneys and allows protein to leak from the blood into urine. However, glomerulosclerosis is one of many causes of proteinuria. A kidney biopsy (removal of tiny part of kidney with a needle) may be necessary to determine whether a patient has glomerulosclerosis or another kidney problem. About 15 percent of people with proteinuria turn out to have glomerulosclerosis.

Both children and adults can develop glomerulosclerosis and it can result from different types of kidney conditions. One frequently encountered type of glomerulosclerosis is caused by diabetes. Drug use or infections may cause focal segmental glomerulosclerosis (FSGS), a very chronic kidney condition. FSGS may also occur in patients with AIDS but most are of unknown cause.

Early stages of glomerulosclerosis may not produce any symptoms but the most important warning sign is proteinuria, usually discovered in routine medical exams. Losing large amounts of protein may cause swelling in the ankles and accumulation of fluid in the abdomen.

Scarred glomeruli cannot be repaired and many patients with glomerulosclerosis get worse over time until their kidneys fail. This condition is called end-stage renal disease (ESRD) and the patients must begin dialysis treatment or receive a kidney transplant. ESRD may be reached within a year or up to ten or more of diagnosis of glomerulosclerosis but time will vary.

Treatments for glomerulosclerosis depend on what caused the scarring of the glomeruli. This is determined by renal biopsy. Immunosuppressive drugs stop proteinuria in some patients, but once the treatments have ended proteinuria will continue. The drugs may sometimes damage the patient's kidneys even more.

Controlling the patient's blood pressure may control the progression of kidney failure. ACE inhibitors, a type of blood pressure medicine, preserve kidney function in patients with diabetes. ACE inhibitors may also slow down kidney failure for patients without diabetes. Low protein diets may also lighten the work done by kidneys to process waste. Some patients will need to control their cholesterol through diet or both diet and medicine.

There are currently several known genetic causes of the hereditary forms of FSGS.

Some researchers found SuPAR as a cause of FSGS.

Another gene that has been associated with this syndrome is the COL4A5 gene.

Sickle cell nephropathy is a type of nephropathy associated with sickle cell disease which causes kidney complications as a result of sickling of red blood cells in the small blood vessels. The hypertonic and relatively hypoxic environment of the renal medulla, coupled with the slow blood flow in the vasa recta, favors sickling of red blood cells, with resultant local infarction (papillary necrosis). Functional tubule defects in patients with sickle cell disease are likely the result of partial ischemic injury to the renal tubules.

Also the sickle cell disease in young patients is characterized by renal hyperperfusion, glomerular hypertrophy, and glomerular hyperfiltration. Many of these individuals eventually develop a glomerulopathy leading to glomerular proteinuria (present in as many as 30%) and, in some, the nephrotic syndrome. Co-inheritance of microdeletions in the -globin gene (thalassemia) appear to protect against the development of nephropathy and are associated with lower mean arterial pressure and less protein in the urine.

Mild increases in the blood levels of nitrogen and uric acid can also develop. Advanced kidney failure and high blood urea levels occur in 10% of cases. Pathologic examination reveals the typical lesion of "hyperfiltration nephropathy" namely, focal segmental glomerular sclerosis. This finding has led to the suggestion that anemia-induced hyperfiltration in childhood is the principal cause of the adult glomerulopathy. Nephron loss secondary to ischemic injury also contributes to the development of azotemia in these patients.

In addition to the glomerulopathy described above, kidney complications of sickle cell disease include cortical infarcts leading to loss of function, persistent bloody urine, and perinephric hematomas. Papillary infarcts, demonstrable radiographically in 50% of patients with sickle trait, lead to an increased risk of bacterial infection in the scarred kidney tissues and functional tubule abnormalities. The presence of visible blood in the urine without pain occurs with a higher frequency in sickle trait than in sickle cell disease and likely results from infarctive episodes in the renal medulla. Functional tubule abnormalities such as nephrogenic diabetes insipidus result from marked reduction in vasa recta blood flow, combined with ischemic tubule injury. This concentrating defect places these patients at increased risk of dehydration and, hence, sickling crises. The concentrating defect also occurs in individuals with sickle trait. Other tubule defects involve potassium and hydrogen ion excretion, occasionally leading to high blood potassium, metabolic acidosis, and a defect in uric acid excretion which, combined with increased purine synthesis in the bone marrow, results in high blood uric acid levels.

The median time to progression to end stage renal disease is 2.7 years. After 5 years, about 37% of patients with LCDD are alive and do not have end stage renal disease.

It is the most common genetic cause of end stage renal disease (renal failure) in childhood and adolescence.

Familial disorders

- Cystinosis

- Galactosemia

- Glycogen storage disease (type I)

- Hereditary fructose intolerance

- Lowe syndrome

- Tyrosinemia

- Wilson's disease

Acquired disorders

- Amyloidosis

- Multiple myeloma

- Paroxysmal nocturnal hemoglobinuria

- Toxins, such as HAART, ifosfamide, lead, and cadmium