Artículo
BK virus after kidney transplant
BK virus is a common virus that most people get in childhood. It usually does not cause problems in healthy people. The virus can stay in your body for life, undetected in the kidneys and urinary tract. But after a kidney transplant, the medicines you take to prevent your body from rejecting the new kidney can weaken your immune system, your body's defense system, causing the BK virus to become active. This can allow the virus to multiply and potentially damage your transplanted kidney. BK virus is not something you can catch after your transplant, it typically becomes active or one that comes with the donated organ. Regular testing can help your health care team find it early and treat it as soon as possible.
- Revisión médica de
- Shahzia Lakhani
- Última actualización
- April 24, 2026
What is BK virus?
BK polyomavirus, also called BKV, is very common. Most people get it as children and the symptoms are usually dismissed as a common cold. After the first infection, the virus usually stays inactive in the body. It often remains in the kidneys and urinary tract, including the bladder and ureters. In healthy people, it usually does not cause symptoms or serious health problems.
Why is BK virus a concern after kidney transplant?
The BK virus is very common. About 90% of adults have had it at some point in their lives.
In some transplant recipients, it can lead to kidney damage and loss of kidney function as the BKV may reactivate in immunocompromised individuals or those with a weakened immune system. After a kidney transplant, you need anti-rejection medicines to protect your new kidney. These medicines help stop your immune system (the body's defense system) from attacking the transplanted kidney. By weakening your body's immune function, these medicines make individuals immunocompromised and make it harder for your body to fight infections. This is most likely in the first year after transplant, when anti-rejection treatment is strongest.
"Immunosuppression that silences rejection can awaken BK virus. Your lab appointments to monitor your kidney function, transplant drug levels, and BK virus screening matter." – Shahzia Lakhani, Senior Director of Clinical Education
How can BK virus harm a transplanted kidney?
When BK virus becomes active, it can spread through the body in stages. It may first show up in the urine and in some people, it then enters the blood. If the infection keeps growing, it can damage the transplanted kidney. This is called BK virus-associated nephropathy (BKVAN). BK virus can slowly reduce how well your transplanted kidney works and can cause ureteral stenosis, (narrowing of the tube that carries urine from the kidney to the bladder) which can also cause pain. Sometimes this damage happens before you even notice any symptoms.
What symptoms should I watch for?
Some people with BK virus do not have symptoms in early stages. Others may notice signs of infection or urinary changes. This is why regular monitoring is so important.
Tell your transplant team right away (don't wait for your next scheduled appointment) if you have:
- Changes in urine color (urine that looks red or brown)
- Burning or pain when urinating
- Pain or tenderness over the kidney area
- Trouble urinating or need to urinate more often than usual or at night
- Changes in vision, usually blurry vision or light sensitivity
- Cough, cold or flu-like symptoms or trouble breathing
- Fever over 38 degrees C (100.4F)
- Muscle pain
- Weakness
- Seizures
These symptoms do not always mean you have BK virus. But after transplant, it is important to report any signs of infection.
How will my health care team test for BK virus?
Your health care team may check for BK virus before and after transplant regularly using blood and urine tests. After a transplant, regular testing is important since the virus can become active before you feel sick. Most transplant centers screen every 1 to 3 months for the first 1 to 2 years after transplant, then less frequently thereafter.
Testing may include:
- Urine tests to monitor for blood in the urine and to detect BK virus
- Blood tests to monitor creatinine levels and BK virus in the bloodstream
- A kidney biopsy if blood levels of BK virus are high or kidney function is worsening, a biopsy may be done to check for kidney damage (BKVAN)
Who is more likely to get BK virus after transplant?
Some things can raise the risk of BK virus becoming active after kidney transplant, including:
- Older age
- diabetes
- Other conditions that weaken the immune system, like lupus, rheumatoid arthritis, and Crohn's disease
- Certain donor-recipient immune system differences
- Receiving a kidney from a deceased donor who may have had BK virus
- Injury caused by changes in blood flow during transplant
- Use of a ureteral stent, a thin, flexible tube put in the ureter to allow urine to move from the kidney to bladder
- Episodes of acute rejection requiring high doses of steroids
- Your transplant team can help you understand your personal risk.
How is BK virus treated?
There is no specific medicine that consistently cures BK virus after a kidney transplant.
The main treatment is usually lowering the strength of anti-rejection medicines. This can help your immune system fight the virus better. Lowering anti-rejection medicines too much can raise the risk of rejection, so treatment may be changed step by step, with close monitoring and follow-up. Some anti-viral medicines may help clear the virus but may affect the kidney function. IVIG may be used to neutralize antibody levels against BK virus.There are medicines being studied in advanced clinical trials to treat BK virus infection in kidney transplant recipients.
Early detection gives your health care team the best chance to protect your transplanted kidney. BK virus can cause damage before you notice symptoms. Regular lab tests can help find the virus early, so your treatment can be adjusted before more damage happens.
Can BK virus be prevented?
Regular screening is one of the best ways to lower the risk of serious BK virus complications after transplant.
You can also help protect your health by:
- Going to all follow-up visits
- Getting lab work done on time
- Taking your medicines exactly as prescribed
- Telling your transplant team right away if you notice symptoms or signs of infection
What questions should I ask my transplant team?
You may want to ask:
- How often will I be tested for BK virus?
- What symptoms should I report right away?
- What is my risk for BK virus?
- What happens if BK virus is found in my urine or blood?
- Will treatment change my anti-rejection medicines?
When should I call my transplant team?
Call your transplant team if you have signs of infection, changes in urination or any new symptoms that concern you. Even if you feel well, regular testing is still important. BK virus can sometimes damage a transplanted kidney without causing clear symptoms.