What is nephrotic syndrome?

What is nephrotic syndrome?

In this article we will describe what is nephrotic syndrome.

1. Definition

Nephrotic syndrome occurs when there are high levels of protein in the urine (proteinuria). Nephrotic syndrome is diagnosed by a triad of:

• A urine ACR of over 220 mg/mmol
• A low albumin level (less than 30 g/L) in the blood
• Ankle swelling.

Ankle swelling is the key symptom of nephrotic syndrome.

Hyperlipidaemia (elevated levels of fats in the blood) is also common.

It is usually due to diabetes or more rarely, a chronic (long term) glomerulonephritis (GN) – see point 2.

This is a group of autoimmune diseases, that usually needs a kidney (renal) biopsy to diagnose.

2. Causes

Nephrotic syndrome can be caused by:

• Autoimmune kidney diseases – called chronic glomerulonephritis (or ‘GN’). Examples include minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), membranous nephropathy; or
• Systemic (whole body) diseases – like diabetes and systemic lupus erythematosus (SLE).

All these diseases are primarily glomerular, i.e. they damage the glomeruli of the kidneys.

3. Proteinuria (protein in urine)

One of the hallmarks of nephrotic syndrome is the significant loss of protein in the urine. This is called proteinuria. It leads to low levels of protein, especially albumin, in the blood. The albumin level is characteristically below 30 g/l.

4. Oedema (swelling)

Due to the loss of proteins like albumin, the oncotic pressure in the blood vessels decreases, causing fluid to leak out into the surrounding tissues, leading to oedema. Oedema often first appears around the eyes and in the ankles and feet.

5. Hyperlipidaemia

Nephrotic syndrome can result in elevated levels of cholesterol and triglycerides in the blood. This occurs due to the liver’s response to the decreased levels of proteins in the blood.

6. Diagnosis

Diagnosis involves clinical assessment (history and examination) by a hospital kidney specialist (called a nephrologist); urine tests to measure proteinuria (urinary ACR); blood tests to check kidney function, and for low albumin levels and high lipid levels.

In some patients, a renal (kidney) biopsy may be needed to determine the underlying cause.

Measuring kidney function with a blood test called ‘urea and electrolytes (U+Es)’ is also vital, as some patients also have long-term impairment of kidney function (CKD). A few of those will go on to need dialysis or a kidney transplant.

7. Treatment

Treatment aims to reduce proteinuria, reduce swelling with water tablets (diuretics), and address the underlying cause.

Medications like angiotensin-converting enzyme inhibitors (ACE inhibitors) or angiotensin receptor blockers (ARBs) are also usually prescribed.

Most patients will need an HMG CoA reductase inhibitor (‘statin’). Also, if the blood albumin is below 20 g/L, tablets to thin the blood will usually be given.

In adults, however, if nephrotic syndrome is due to glomerulonephritis (GN), patients may need treatment with prednisolone and other stronger immunosuppressive drugs, such as azathioprine, mycophenolate, ciclosporin and cyclophosphamide.

In children, 80% of cases of nephrotic syndrome are caused by a GN called minimal change disease, which can be successfully treated with prednisolone (a steroid). It then usually goes away. A renal biopsy is usually not done in children with NS.

Note. There is no evidence that limiting protein in the diet helps to reduce the protein loss in the urine.

8. Complications

Nephrotic syndrome can lead to several complications, such as an increased risk of infection due to loss of immunoglobulins, blood clots (e.g. DVTs in the legs, and PEs in the lungs) due to increased blood thickening, and malnutrition due to protein loss.

9. Paediatric presentation

Nephrotic syndrome can present in children as well, with most cases occurring between the ages of 2 and 6. The most common cause in children is a form of GN called minimal change disease (MCD).

10. Prognosis

The prognosis for nephrotic syndrome varies depending on the underlying cause and how well it responds to treatment.

Nephrotic syndrome may go away once the underlying cause, if known, has been treated. Others may become chronic and require ongoing management.

If you suspect you or someone you know has nephrotic syndrome, it is important to be referred to a nephrologist for a clear diagnosis and management plan.

Summary

We have described what is nephrotic syndrome. We hope it has been helpful.

 

Last Reviewed on 24 May 2024