BK nephropathy

Find out about BK nephropathy: symptoms, diagnosis, treatment and sources of further information and support.

What is BK nephropathy?

BK nephropathy is a condition that can occur after a kidney transplant. It is caused by the activation of the BK virus. This is a very common virus, and nine out of 10 people catch it during childhood in the same way as you catch a cold. The virus is carried in the body for life, but it usually remains inactive and causes no symptoms.

The virus was first identified in a kidney transplant recipient with the initials BK.

After a kidney transplant, medicines are taken to suppress the immune system and prevent the body from rejecting the new kidney. Because of the suppressed immune system, the BK virus can become active and affect the transplanted kidney.

BK nephropathy affects around 1 in 20 people who have received a kidney transplant. It usually develops between 6 and 12 months after a transplant.

What are the signs and symptoms of BK nephropathy?

There are often no noticeable symptoms of BK nephropathy itself, but there may be an unexpected drop in kidney function.

Half of all people with BK nephropathy will have protein in the urine (proteinuria) and one in five will have blood in the urine (haematuria). This is likely to be seen only under a microscope or when tested by dipping a specially treated paper strip into the urine (urine dipstick).

If it is left untreated, BK nephropathy can cause inflammation in the transplanted kidney and a narrowing of the tube between the transplanted kidney and bladder (ureteral stenosis). This can cause the body to reject the new kidney.

What causes BK nephropathy?

BK nephropathy is caused by an activation of the BK virus, but it is not currently known why the virus becomes active in some people and not others. It may be because some donor kidneys contain higher levels of the virus than others, or because of changes in the virus that make it more likely to cause disease.

How is BK nephropathy diagnosed?

Activation of the BK virus can be diagnosed by blood and urine tests. Regular blood and urine tests after a kidney transplant check for the virus, especially in the first 12 months.

A definitive diagnosis can only be made by a biopsy of the transplant kidney, which can also show how severe the damage is.

Does BK nephropathy affect other parts of the body?

BK nephropathy is only known to affect the kidneys.

Does BK nephropathy run in families?

BK nephropathy itself is not a genetic condition so it cannot be inherited. However, it is possible that some people are genetically more likely to be affected by the virus that others, perhaps due to differences in their immune systems.

How is BK nephropathy treated?

It is not currently possible to cure or get rid of the BK virus once it has been caught. If BK nephropathy develops after a kidney transplant, the anti-rejection medicines that are normally prescribed to suppress the immune system are likely to be reduced. This might involve stopping one of the immunosuppression tablets.

Specific antiviral medicines may also be prescribed, such as cidofovir, ciprofloxacin, leflunomide or intravenous immunoglobulin.

Early diagnosis and treatment help to protect kidney function.

Where can I get more information or support about BK nephropathy?

For more information on BK nephropathy including its diagnosis, symptoms and treatment, visit Edinburgh Renal Unit - BK virus nephropathy.

You can also watch a July 2023 patient information session about BK virus research from Kidney Research.

Publication date: 11/2023

Review date: 11/2026

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