• Proteinuria (Nephrotic syndrome is arbitrarily defined as urinary protein loss of greater than 3.5 g/day)
• Hypoalbuminemia
• High levels of cholesterol (hypercholesterolemia), specifically elevated LDL, usuallywith concomitantly elevated VLDL
• Lipiduria
• Coagulation abnormalities: renal vein thrombosis more common than thrombosis in nonrenal circulation.
• Lower Back pain, usually in the kidney or bladder area.

Diagnosis

High urine levels of protein can readily be detected with a dipstick. The best way to make a diagnosis is to quantify the amount of protein in a 24-hour urine sample or a randomly sampled urine albumin to creatinine ratio (ACR). A diagnosis of nephrotic syndrome requires more than 3.5 grams of proteinuria per 1.73 square meter surface area in adults. It is important to note, however, that nephrotic syndrome can be associated with lesser degrees of proteinuria, and many of the complications of nephrotic syndrome are due to hypoalbuminemia and the resultant decreased plasma oncotic pressure. Therefore, the same consequences can result independently of the level of proteinuria, as long as the same degree of hypoalbuminemia is achieved.

Once the diagnosis of nephrotic syndrome is reached, further investigations must focus on the underlying disease process.

Pathogenesis

The glomeruli of the kidneys are the parts that normally filter the blood. They consist of capillaries that are fenestrated (leaky, due to little holes called fenestrae or windows) and that allow fluid, salts, and other small solutes to flow through, but normally not proteins.

In nephrotic syndrome, the glomeruli become damaged due to diabetes, glomerulonephritis, or even prolonged hypertension (high blood pressure) so that small proteins, such as albumin can pass through the kidneys into urine.

Nephrotic syndrome is characterised by proteinuria (detectable protein in the urine), and low albumin levels in blood plasma. As a compensation, the liver begins to make more of all its proteins, and levels of large proteins (such as alpha 2-macroglobulin) increase.

Edema usually occurs due to salt and water retention by the diseased kidneys as well as sometimes due to the reduced colloid oncotic pressure (because of reduced albumin in the plasma). Edema may also be caused by CHF. However, CHF patients cannot tolerate lying flat and thus do not develop puffiness in the face.

Cholesterol levels are also increased, and though the mechanism isn't fully understood, it is thought to be due to the increased synthesis of lipoproteins in the liver. The excess lipoproteins end up in the urine filtrate, which is then rebsorbed by the tubular cells, which end up shedding and forming oval fat bodies or fatty casts.

There is an increased tendency for thrombosis (up to 25%), perhaps due to urinary loss of inhibitors of clotting such as antithrombin III, as well as hypovolaemia due to movement of water from plasma into tissue (causing edema).

Similar loss of immunoglobulins increases the risks of infections and relevant immunisation is recommended against pneumococcus, Haemophilus influenzae, and meningococcus.

Differential diagnosis

Primary renal diseases

Minimal change disease: The most common cause (80%) of nephrotic syndrome in children. It is so called because on renal biopsy there is no change on light microscopy, only electron microscopy reveals fusion of foot processes.
Membranous glomerulonephritis: The most common primary renal cause of nephrotic syndrome in adults in developing countries.
Focal segmental glomerulosclerosis
Membranoproliferative glomerulonephritis
Mesangial proliferative glomerulonephritis
IgA nephropathy

Secondary renal diseases

Others

Treatment

When treating nephrotic syndrome, if the underlying problem is apparent, (e.g. hypertension, diabetes) then this should be addressed. Some types of nephrotic syndrome respond to therapy with steroids (especially minimal change disease) and/or other immunosuppressive therapy. Others are followed up in clinic with management of blood pressure, cholesterol levels, coagulation problems and renal failure. In most types of nephrotic syndrome, the protein excretion improves with the use of ACE inhibitor medication. This is generally used for the treatment of hypertension, but can also improve protein loss, even if the blood pressure is normal. Dietary modification, including sodium or salt restriction and lower protein intake, can benefit the symptoms of nephrotic syndrome as well.

Diuretics and intravenous albumin may be needed. Furosemide (1 mg/kg/d) and spironolactone (2 mg/kg/d) are not always indicated but may help when fluid retention is severe, provided no signs of renal failure or volume contraction are evident. Achieving a satisfactory diuresis is difficult when the patient's serum albumin level is less than 1.5 g/dL. An effective regimen is to give salt-poor albumin at 1 g/kg, followed by intravenous furosemide. Close monitoring is obligatory to prevent pulmonary edema. Some evidence suggests that albumin may delay the response to steroids and may even induce more frequent relapses, probably by causing severe glomerular epithelial damage. The time required for remission is prolonged with a longer duration of administration and larger volumes of infused albumin. Fluid removal and weight loss remain transient unless proteinuria remits.

Prognosis

The prognosis depends on the cause of nephrotic syndrome. It is usually good in children, because minimal change disease responds very well to steroids and does not cause chronic renal failure. However 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).

 

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