Membranous nephropathy: symptoms, tests and treatment in the UK

The kidneys filter the blood through tiny units called glomeruli. Kidney Research UK explains that when the glomeruli are damaged, large amounts of protein can leak into the urine, causing low protein levels in the blood and fluid retention, a picture called nephrotic syndrome. Membranous glomerulonephritis is one of the kidney diseases it lists as a cause.

The UK Kidney Association describes membranous nephropathy (MN) as a disorder of the immune system in which the kidneys leak a lot of protein, while normal urine has only traces. In most adults the cause is not found. When no tumour, drug or underlying medical condition can be identified, the clinician page says the condition is labelled primary (idiopathic) MN. When there is a cause, it is described as secondary MN.

The word membranous refers to the thickening of the filtering membrane seen under the microscope on biopsy. It is not the same as minimal change disease, which is the usual cause of nephrotic syndrome in children according to the NHS.

The UK Kidney Association says MN develops slowly and people may not realise they have it. Some are found simply because a lot of protein is detected in the urine after a routine test. When symptoms occur they result from protein loss and fluid retention.

• Very frothy urine, which the UK Kidney Association likens to the head on a pint of beer.

• A puffy face, particularly swollen eyelids first thing in the morning.

• A distended tummy and swollen ankles, especially in the evenings.

• High blood pressure, which GPs may find.

• Tiredness, and few other symptoms unless kidney failure is advanced.

See a GP if you notice persistent frothy urine, unexplained swelling of the eyes, face or legs, or if a routine urine test shows protein. The UK Kidney Association says these complaints often trigger a GP visit and that simple blood and urine tests can confirm nephrotic syndrome. Its clinician page notes that protein of 1+ or more on a dipstick in someone with no symptoms makes significant kidney disease very likely, and is not adequately explained as a urine infection.

Complications can be serious. The UK Kidney Association clinician page mentions susceptibility to infection or thrombosis as complications of nephrotic syndrome, and Kidney Research UK lists blood clots, high cholesterol and infections. As general safety advice, a swollen painful leg, sudden breathlessness or chest pain could indicate a clot and should be treated as an emergency: call 999. Getting short of breath because of fluid, as Kidney Research UK notes can happen with water around the lungs, also needs prompt assessment.

Kidney Research UK says blood and urine tests can confirm nephrotic syndrome by showing large amounts of protein in the urine and low levels in the blood, along with raised cholesterol, and that a kidney biopsy may be required to confirm the exact cause. Once the GP has identified nephrotic syndrome or heavy proteinuria, the UK Kidney Association says the patient will be referred to a kidney specialist, and that a range of disorders can present in a similar manner.

The UK Kidney Association says the precise diagnosis can only be made with a kidney biopsy, in which characteristic features confirm MN. The clinician page says that the availability of blood tests for anti-PLA2R and anti-THSD7A autoantibodies holds promise for non-invasive diagnosis and monitoring of primary MN in the future. Because secondary causes matter, the clinician page stresses inquiry into drugs, including over-the-counter NSAIDs, and the search for infection or malignancy; in one patient story on the patient page, tests for HIV, hepatitis, lupus and scans for cancer were done to look for underlying causes.

The UK Kidney Association says there is a lot that can be done to improve wellbeing even if it does not address the root cause. Most patients receive an ACE inhibitor or angiotensin receptor blocker (ARB). Originally designed for high blood pressure, these also reduce urine protein loss and allow albumin in the blood to improve. Diuretics (water tablets) help control swelling and work together with these medicines, and nutritional support helps strengthen bones and muscles. Kidney Research UK adds salt restriction, medicines to lower cholesterol, antibiotics to reduce infection risk and, for some, anticoagulant treatment to reduce clot risk.

Because between 25% and 40% of people improve on their own, the UK Kidney Association says patients need to be closely monitored. For those who do not improve, a wide range of immune-suppressing drugs may be used, though it says there is a lack of good-quality trial information about them, particularly newer medicines such as rituximab and Benlysta, and responses vary and are hard to predict. The clinician page says that treatment targets the immune system so potential toxicities are considerable, and that there is controversy about the optimal approach and which patients should be offered active therapy, with many experts reserving aggressive therapy for those whose kidney function is deteriorating.

If kidney damage progresses, the UK Kidney Association says kidney replacement therapy, dialysis or a kidney transplant, becomes necessary. It says MN can recur in the transplanted kidney and that this cannot currently be predicted, but that overall a transplant remains the best option for most people with MN who have lost kidney function.

Living with MN usually involves regular blood and urine tests, blood pressure monitoring and tablets taken long-term. The patient stories on the UK Kidney Association page describe making changes to salt intake and diet, and the importance of the medical team monitoring kidney function.

In the NHS, care is led by a nephrologist, with referral from the GP, and specialist units deal with immune-suppressing treatment and kidney biopsy. Private nephrology opinions can support diagnosis and treatment decisions, but monitoring and treatment of a long-term condition like MN is usually shared with the NHS renal unit that holds your records.