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Overview of Nephrotic Syndrome

By

Frank O'Brien

, MD, Washington University in St. Louis

Last full review/revision Jul 2021| Content last modified Jul 2021
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Nephrotic syndrome is urinary excretion of > 3 g of protein/day due to a glomerular disorder plus edema and hypoalbuminemia. It is more common among children and has both primary and secondary causes. Diagnosis is by determination of urine protein/creatinine ratio in a random urine sample or measurement of urinary protein in a 24-hour urine collection; cause is diagnosed based on history, physical examination, serologic testing, and renal biopsy. Prognosis and treatment vary by cause.

Etiology

The most common primary causes are the following:

Secondary causes account for < 10% of childhood cases but > 50% of adult cases, most commonly the following:

Table
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Pathophysiology

Proteinuria occurs because of changes to capillary endothelial cells, the glomerular basement membrane (GBM), or podocytes, which normally filter serum protein selectively by size and charge.

The mechanism of damage to these structures is unknown in primary and secondary glomerular diseases, but evidence suggests that T cells may upregulate a circulating permeability factor or downregulate an inhibitor of permeability factor in response to unidentified immunogens and cytokines. Other possible factors include hereditary defects in proteins that are integral to the slit diaphragms of the glomeruli, activation of complement leading to damage of the glomerular epithelial cells and loss of the negatively charged groups attached to proteins of the GBM and glomerular epithelial cells.

Complications of nephrotic syndrome

The disorder results in urinary loss of macromolecular proteins, primarily albumin but also opsonins, immunoglobulins, erythropoietin, transferrin, hormone-binding proteins (including thyroid-binding globulin and vitamin D-binding protein), and antithrombin III. Deficiency of these and other proteins contribute to a number of complications (see table Complications of Nephrotic Syndrome Complications of Nephrotic Syndrome Nephrotic syndrome is urinary excretion of > 3 g of protein/day due to a glomerular disorder plus edema and hypoalbuminemia. It is more common among children and has both primary and secondary... read more ); other physiologic factors also play a role.

Table
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Symptoms and Signs

Primary symptoms include anorexia, malaise, and frothy urine (caused by high concentrations of protein).

Fluid retention may cause

Corresponding signs may develop, including peripheral edema and ascites. Edema may obscure signs of muscle wasting and cause parallel white lines in fingernail beds (Muehrcke lines).

Diagnosis

  • Urine random (spot) protein/creatinine ratio 3 or proteinuria 3 g/24 hours

  • Serologic testing and renal biopsy unless the cause is clinically obvious

Urine testing

A finding of significant proteinuria (3 g protein in a 24-hour urine collection) is diagnostic (normal excretion is < 150 mg/day). Alternatively, the protein/creatinine ratio in a random urine specimen usually reliably estimates grams of protein/1.73 m2 body surface area (BSA) in a 24-hour collection (eg, values of 40 mg/dL protein and 10 mg/dL [884 micromol/L] creatinine in a random urine sample are equivalent to the finding of 4 g/1.73 m2 in a 24-hour specimen).

Calculations based on random specimens may be less reliable when creatinine excretion is high (eg, during athletic training) or low (eg, in cachexia). However, calculations based on random specimens are usually preferred to 24-hour collection because random collection is more convenient and less prone to error (eg, due to lack of adherence); more convenient testing facilitates monitoring changes that occur during treatment.

Besides proteinuria, urinalysis may demonstrate casts (hyaline, granular, fatty, waxy, or epithelial cell). Lipiduria, the presence of free lipid or lipid within tubular cells (oval fat bodies), within casts (fatty casts), or as free globules, suggests a glomerular disorder causing nephrotic syndrome. Urinary cholesterol can be detected with plain microscopy and demonstrates a Maltese cross pattern under crossed polarized light; Sudan staining must be used to show triglycerides.

Adjunctive testing in nephrotic syndrome

Adjunctive testing helps characterize severity and complications.

  • Blood urea nitrogen (BUN) and creatinine concentrations vary by degree of renal impairment.

  • Serum albumin often is < 2.5 g/dL (25 g/L).

  • Total cholesterol and triglyceride levels are typically increased.

It is not routinely necessary to measure levels of alpha- and gamma-globulins, immunoglobulins, hormone-binding proteins, ceruloplasmin, transferrin, and complement components, but these levels may also be low.

Testing for secondary causes of nephrotic syndrome

The role of testing for secondary causes of nephrotic syndrome (see table Causes of Nephrotic Syndrome Causes of Nephrotic Syndrome Nephrotic syndrome is urinary excretion of > 3 g of protein/day due to a glomerular disorder plus edema and hypoalbuminemia. It is more common among children and has both primary and secondary... read more ) is controversial because yield may be low. Tests are best done as indicated by clinical context. Tests may include the following:

Test results may alter management and preclude the need for biopsy. For example, demonstration of cryoglobulins suggests mixed cryoglobulinemia (eg, from chronic inflammatory disorders such as systemic lupus erythematosus Systemic Lupus Erythematosus (SLE) Systemic lupus erythematosus is a chronic, multisystem, inflammatory disorder of autoimmune etiology, occurring predominantly in young women. Common manifestations may include arthralgias and... read more Systemic Lupus Erythematosus (SLE) , Sjögren syndrome Sjögren Syndrome Sjögren syndrome is a relatively common chronic, autoimmune, systemic, inflammatory disorder of unknown cause. It is characterized by dryness of the mouth, eyes, and other mucous membranes due... read more Sjögren Syndrome , or hepatitis C virus Hepatitis C, Chronic Hepatitis C is a common cause of chronic hepatitis. It is often asymptomatic until manifestations of chronic liver disease occur. Diagnosis is confirmed by finding positive anti-HCV and positive... read more infection), and demonstration of a monoclonal protein on serum or urine protein electrophoresis suggests a monoclonal gammopathy (eg, multiple myeloma Multiple Myeloma Multiple myeloma is a cancer of plasma cells that produce monoclonal immunoglobulin and invade and destroy adjacent bone tissue. Common manifestations include lytic lesions in bones causing... read more Multiple Myeloma ), especially in patients > 50 years who have anemia Overview of Decreased Erythropoiesis Anemia, a decrease in the number of red blood cells (RBCs), hemoglobin (Hb) content, or hematocrit (Hct), can result from decreased RBC production (erythropoiesis), increased RBC destruction... read more .

Prognosis

Prognosis varies by cause. Complete remissions may occur spontaneously or with treatment. The prognosis generally is favorable in corticosteroid-responsive disorders.

In all cases, prognosis may be worse in the presence of the following:

  • Infection

  • Hypertension

  • Significant azotemia

  • Hematuria

  • Thromboses in cerebral, pulmonary, peripheral, or renal veins

Treatment

  • Treatment of causative disorder

  • Angiotensin inhibition

  • Sodium restriction

  • Statins

  • Diuretics for excessive fluid overload

  • Rarely, nephrectomy

Treatment of disorder causing nephrotic syndrome

Treatment of underlying disorders may include prompt treatment of infections (eg, staphylococcal endocarditis, malaria, syphilis, schistosomiasis), and stopping drugs (eg, gold, penicillamine, nonsteroidal anti-inflammatory drugs [NSAIDs]); these measures may cure nephrotic syndrome in specific instances.

Proteinuria treatment

Angiotensin inhibition (using angiotensin-converting enzyme [ACE] inhibitors or angiotensin II receptor blockers [ARBs]) is indicated to reduce systemic and intraglomerular pressure and proteinuria. These drugs may cause or exacerbate hyperkalemia Hyperkalemia Hyperkalemia is a serum potassium concentration > 5.5 mEq/L (> 5.5 mmol/L), usually resulting from decreased renal potassium excretion or abnormal movement of potassium out of cells. There are... read more in patients with moderate to severe renal insufficiency.

Protein restriction is not recommended because of lack of demonstrated effect on progression.

Edema treatment

Sodium restriction (< 2 g sodium, or about 100 mmol/day) is recommended for patients with symptomatic edema.

Loop diuretics are usually required to control edema but may worsen preexisting renal insufficiency and hypovolemia, hyperviscosity, and hypercoagulability and thus should be used only if sodium restriction is ineffective or there is evidence of intravascular fluid overload. In severe cases, of nephrotic syndrome, IV albumin infusion followed by a loop diuretic may also be given to control edema.

Dyslipidemia treatment

Hypercoagulability treatment

Anticoagulants are indicated for treatment of thromboembolism, but few data exist to support their use as primary prevention.

Management of infection risk

All patients should receive pneumococcal vaccination if not otherwise contraindicated.

Nephrectomy for nephrotic syndrome

Rarely, bilateral nephrectomy is necessary in severe nephrotic syndrome because of persistent hypoalbuminemia. The same result can sometimes be achieved by embolizing the renal arteries with coils, thus avoiding surgery in high-risk patients. Dialysis Hemodialysis In hemodialysis, a patient’s blood is pumped into a dialyzer containing 2 fluid compartments configured as bundles of hollow fiber capillary tubes or as parallel, sandwiched sheets of semipermeable... read more is used as necessary.

Key Points

  • Nephrotic syndrome is most common in young children, is usually idiopathic, and is most often minimal change disease.

  • In adults, nephrotic syndrome is usually secondary, most often to diabetes or preeclampsia.

  • Consider nephrotic syndrome in patients, particularly young children, with unexplained edema or ascites.

  • Confirm nephrotic syndrome by finding spot protein/creatinine ratio 3 or urinary protein 3 g/24 hours.

  • Do tests for secondary causes and renal biopsy selectively, based on clinical findings.

  • Assume minimal change disease if a child with idiopathic nephrotic syndrome improves after treatment with corticosteroids.

  • Treat the causative disorder with angiotensin inhibition, sodium restriction, and often diuretics and/or statins.

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