Overview 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 ); other physiologic factors also play a role.

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 helps characterize severity and complications.

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.

The role of testing for secondary causes of nephrotic syndrome (see table Causes of Nephrotic Syndrome Causes of Nephrotic Syndrome ) 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 , 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 ... read more , 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 ), 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 .

Renal biopsy Renal biopsy Biopsy of the urinary tract requires a trained specialist (nephrologist, urologist, or interventional radiologist). Indications for diagnostic biopsy include unexplained nephritic or nephrotic... read more is indicated in adults to diagnose the disorder causing idiopathic nephrotic syndrome. Idiopathic nephrotic syndrome in children is most likely minimal change disease Minimal Change Disease Minimal change disease causes abrupt onset of edema and heavy proteinuria, mostly in children. Renal function is typically normal. Diagnosis is based on clinical findings or renal biopsy. Prognosis... read more and is usually presumed without biopsy unless the patient fails to improve during a trial of corticosteroids. Specific biopsy findings are discussed under the individual disorders.

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.

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... read more in patients with moderate to severe renal insufficiency.

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

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.

Statins are indicated for dyslipidemia Dyslipidemia Dyslipidemia is elevation of plasma cholesterol, triglycerides (TGs), or both, or a low high-density lipoprotein cholesterol level that contributes to the development of atherosclerosis... read more .

Limitation of saturated fat and cholesterol intake is recommended to help control dyslipidemia.

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