What is nephrotic syndrome? 

Nephrotic syndrome is a clinical condition where the kidneys leak large amounts of protein into the urine, leading to low protein levels in the blood and significant swelling in the body. It is not a disease itself but a sign that the small filtering units of the kidneys, known as glomeruli, are not working correctly. 

Nephrotic syndrome occurs when the filters in your kidneys become damaged, allowing protein (albumin) that should stay in the blood to leak into the urine. This loss of protein causes fluid to build up in the body’s tissues, leading to oedema (swelling), particularly around the eyes and in the ankles. Understanding this condition is vital because, if left unmanaged, it can lead to complications such as blood clots or infections. We will explore the common symptoms, the underlying causes, how it differs from other kidney conditions, and the standard management approaches used within the UK healthcare system. 

What We’ll Discuss in This Article 

• The fundamental definition and mechanism of nephrotic syndrome. 

• The primary signs and symptoms to look out for, such as oedema. 

• Common causes, including primary kidney diseases and secondary factors like diabetes. 

• The difference between nephrotic and nephritic syndromes. 

• Standard diagnostic tests and management strategies. 

• When to seek urgent medical advice for worsening symptoms. 

What are the symptoms of nephrotic syndrome? 

Nephrotic syndrome is primarily characterised by a triad of clinical features: heavy proteinuria (high protein in urine), hypoalbuminaemia (low protein in blood), and peripheral oedema. Patients often notice a frothy appearance to their urine and significant swelling in the lower limbs or around the eyelids, which is usually most prominent in the mornings. 

The most common symptoms experienced by patients include: 

• Oedema: Fluid retention that causes swelling in the ankles, feet, legs, and sometimes the face or hands. 

• Frothy Urine: This is caused by the high concentration of protein being excreted. 

• Fatigue: A general feeling of tiredness or lethargy due to the underlying kidney strain. 

• Weight Gain: Often rapid, caused by the accumulation of excess fluid rather than fat. 

• Loss of Appetite: Feeling full or nauseated due to fluid buildup in the abdomen (ascites). 

Clinical Context 

In clinical practice, the diagnosis is often suspected when a patient presents with sudden-onset swelling. A simple urine dipstick test is frequently the first step to confirm the presence of protein. According to NICE guidelines, further blood tests are then required to check albumin levels and kidney function (eGFR). 

What causes nephrotic syndrome? 

Nephrotic syndrome is caused by damage to the glomeruli, the tiny clusters of blood vessels in the kidneys that filter waste. This damage can be ‘primary’, meaning it starts in the kidneys, or ‘secondary’, meaning it is caused by another condition affecting the body, such as diabetes or lupus. 

Causes are generally categorised into two groups: 

Primary Causes (Kidney-Specific) 

• Minimal Change Disease: The most common cause in children; the damage is so slight it can only be seen under a highly powerful microscope. 

• Focal Segmental Glomerulosclerosis (FSGS): Scarring in specific parts of the kidney filters. 

• Membranous Nephropathy: Thickening of the membranes within the glomeruli. 

Secondary Causes (Systemic Conditions) 

• Diabetes Mellitus: Long-term high blood sugar can damage the kidney filters (diabetic nephropathy). 

• Lupus (Systemic Lupus Erythematosus): An autoimmune condition that can cause kidney inflammation. 

• Amyloidosis: A rare condition where abnormal proteins build up in organs. 

• Infections: Certain viral infections like Hepatitis B, Hepatitis C, or HIV. 

Cause Type	Common Examples	Typical Patient Group
Primary	Minimal Change Disease	Primarily Children
Primary	Membranous Nephropathy	Primarily Adults
Secondary	Diabetic Nephropathy	Adults with long-term Diabetes
Secondary	Lupus Nephritis	Patients with Autoimmune disease

Nephrotic vs Nephritic Syndrome 

It is common to confuse nephrotic syndrome with nephritic syndrome, but they are distinct clinical entities. While nephrotic syndrome is defined by massive protein loss and heavy swelling, nephritic syndrome is characterised by inflammation and the presence of blood in the urine. 

The table below outlines the key differences: 

Feature	Nephrotic Syndrome	Nephritic Syndrome
Main Feature	Heavy Proteinuria (>3.5g/day)	Haematuria (Blood in urine)
Swelling	Severe and widespread (Oedema)	Mild to moderate
Blood Pressure	Usually normal (can be high)	Commonly high (Hypertension)
Urine Appearance	Frothy	Red or ‘cola-coloured’
Primary Issue	Filter ‘leakiness’	Filter ‘inflammation’

Triggers and risk factors for relapses 

While the underlying cause is often an autoimmune response or a chronic disease, certain triggers can cause a ‘relapse’ or worsening of symptoms in people already diagnosed with kidney conditions. These triggers often involve the immune system reacting to external stressors. 

• Infections: Simple upper respiratory tract infections, sore throats, or viral illnesses can trigger a flare-up of Minimal Change Disease. 

• Medications: Certain medications, including non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, can occasionally trigger kidney issues in sensitive individuals. 

• Allergies: In rare cases, severe allergic reactions, such as those from bee stings or certain vaccinations, have been linked to the onset or relapse of nephrotic symptoms. 

• Environmental Factors: Exposure to certain toxins or chemicals has been noted in specific research cases as a potential risk factor for glomerular damage. 

Clinical Management of Relapses 

In the UK, patients who have experienced nephrotic syndrome are often monitored by a nephrologist. If a relapse occurs, a course of corticosteroids is usually the first line of action. It is essential for patients to monitor their urine regularly for protein if they have a known history of the condition. 

How is nephrotic syndrome treated? 

The treatment of nephrotic syndrome focuses on addressing the underlying cause and managing the symptoms to prevent complications. This usually involves a combination of steroid medications to stop the protein leak and lifestyle changes to manage fluid retention. 

• Corticosteroids: Medications like prednisolone are used to reduce inflammation in the kidneys and stop the protein leak. 

• Diuretics: Often called ‘water tablets’, these help the kidneys remove excess fluid from the blood, reducing swelling. 

• ACE Inhibitors or ARBs: These blood pressure medications are also used to reduce the amount of protein lost in the urine. 

• Statins: Since nephrotic syndrome can lead to high cholesterol, statins may be prescribed to protect heart health. 

• Anticoagulants: To reduce the risk of blood clots, which is higher in patients losing significant protein. 

According to the NHS guidance on Nephrotic Syndrome: 

‘Treatment for nephrotic syndrome depends on the cause, but most people are given steroid medicine to stop protein leaking into their urine.’ 

This research was conducted by NHS England and is regularly updated to ensure clinical accuracy for UK patients 

 (Source: https://www.nhs.uk/conditions/nephrotic-syndrome/). 

To Summarise 

Nephrotic syndrome is a condition where damaged kidney filters leak protein into the urine, causing swelling and low blood protein levels. It can be caused by conditions specific to the kidney or systemic diseases like diabetes. Management usually involves treating the underlying cause, using steroids (especially in children), and managing fluid levels with diuretics. 

If you experience severe, sudden, or worsening symptoms, such as difficulty breathing or extreme swelling, call 999 immediately. 

Authority Snapshot 

This article was reviewed by Dr. Stefan Petrov, a UK-trained physician with extensive experience in general medicine and emergency care. We have explored the clinical definitions, symptoms, and causes of nephrotic syndrome in alignment with NHS and NICE clinical knowledge summaries. Our goal is to provide accurate, evidence-based information to help patients understand kidney health and the importance of professional medical monitoring.