Renal vein thrombosis (RVT) is when a blood clot develops anywhere along the renal vein. This is the vein that drains blood from the kidneys. RVT is rare but can be life threatening.

People with renal vein thrombosis (RVT) have a blood clot, also known as a thrombus, in the vein that carries blood away from their kidneys.

If a thrombus grows so large that it completely blocks the renal vein, the kidneys swell and cannot function properly. The person may experience acute pain in their side. They may also notice a reduced need to urinate, and they may have blood in their urine.

The renal veins join the inferior vena cava, which is the main vein returning blood to the heart. If any part of a renal vein thrombosis breaks away from the main clot, it can travel to the lungs. Blood clots here can be fatal.

This article explains what RVT is and how doctors treat it. It also looks at ways of preventing it and reducing the risk factors.

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People with RVT may have clots on just one side, but according to a 2023 paper, most people have clots on both sides.

Although anyone can develop RVT, most people with it have underlying kidney diseases or have had a kidney transplant. Some infections and injuries can also increase the risk of RVT.

Most people with RVT have nephrotic syndrome, where the kidneys leak protein into the urine.

Blood clots can also form if the veins are damaged. This can happen due to a back injury or trauma to the abdomen.

Very occasionally, infants develop RVT, particularly if they are severely dehydrated or have very low blood pressure.

Having nephrotic syndrome significantly increases a person’s risk of developing RVT, according to a 2023 paper. Other risk factors include:

  • having kidney cancer, especially renal cell carcinoma, which can grow into the renal veins
  • being pregnant
  • using estrogen-based birth control
  • having blood clotting disorders, which are also known as hypercoagulability disorders
  • having another kidney disease
  • having a kidney transplant — RVT usually presents within 48 hours of surgery
  • having an inflammatory disorder, such as Behcet syndrome

The Centers for Disease Control and Prevention (CDC) notes that the risk of developing a deep vein thrombosis (DVT), such as RVT, increases with age. They add that some people develop blood clots after having catheter treatment in a central vein.

Healthcare professionals know that people with severe COVID-19 infections, particularly those who require hospital treatment, have a higher chance of blood clots, including RVT and hypercoagulability disorders. In a 2022 case study, healthcare professionals recorded how they successfully treated a person with RVT, which was caused by COVID-19.

Many people with RVT do not have any symptoms, and healthcare professionals discover the blood clots during imaging tests for other purposes. However, when people do experience symptoms, they are often not immediately obvious. Symptoms include:

  • worsening kidney function
  • pain, or tenderness, in the area between the ribs and hips (flank)
  • lower back pain
  • protein in urine
  • blood in urine
  • decreased amount of urine
  • nausea
  • vomiting
  • fever

Healthcare professionals cannot diagnose RVT through a physical exam, but they may be able to feel if the kidneys are swollen. They may also test the person’s urine for proteins and blood.

Researchers explain that healthcare professionals usually recommend imaging tests, including ultrasounds and CT scans. They state that although renal venography is the gold standard test for RVT, many healthcare professionals prefer to use less invasive tests. Renal venography is when a healthcare professional injects a dye into the person’s veins and then takes an X-ray of the kidneys to see how the blood flows.

Doctors may recommend CT angiography, which is a similar test but produces a more detailed picture of the person’s kidneys and blood supply. They may also recommend magnetic resonance angiography (MRA), which is similar to a CT scan but does not use X-rays.

Many people with RVT have an underlying kidney disease, so healthcare professionals tailor their treatments to take that into consideration.

They may prescribe anticoagulants to thin the person’s blood. A 2023 case study records how doctors successfully treated a person’s RVT with rivaroxaban (Xarelto). Healthcare professionals may also prescribe heparin and warfarin to stop other clots from forming.

People with untreated RVT have a risk of kidney damage, which can lead to chronic (long-term) kidney disease.

The CDC notes that if parts of the clot break away, they can travel to the person’s lungs, causing a pulmonary embolism (PE).

PEs can be life threatening and need immediate medical treatment. If a person has difficulty breathing, chest pain that gets worse after coughing, or coughs up blood, they need to see a doctor as this is an emergency.

There is very little research on how to prevent RVT, as most people with it have underlying kidney problems. However, the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) offers some tips for keeping kidneys healthy. These include:

  • treating any underlying kidney problems
  • taking prescribed medications as directed
  • keeping hydrated by drinking lots of water
  • eating a healthy diet with plenty of lean protein, fruit, vegetables, and whole grains
  • maintaining a moderate weight
  • limiting or eliminating alcohol
  • quitting smoking

Most people with RVT respond well to treatment. However, the outlook depends on the underlying cause, and a person may need additional treatment.

Healthcare professionals may continue to prescribe anticoagulants to prevent people from developing additional clots.

A notes in people who have RVT following a kidney transplant, their bodies have usually rejected the organ.

Renal vein thrombosis (RVT) is when a blood clot forms in a person’s renal veins, which take blood away from the kidneys.

It can happen to anyone, but most people with RVT have underlying kidney problems, such as nephrotic syndrome. Other common causes include kidney cancers or having a kidney transplant.

Doctors treat RVT with anticoagulants and will also treat the underlying causes.