What is Renal Vein Thrombosis?
Renal vein thrombosis (RVT) is a rare medical condition where a clot, known as a thrombus, forms in the main veins of the kidneys or their branches. This condition can either show up suddenly or go unnoticed, and has the potential to lead to serious kidney conditions like acute kidney injury or chronic kidney disease. The first description of RVT and its link to protein in the urine (proteinuria) was given by a French kidney specialist, Rayer, in the 1840s.
RVT is often linked to other medical conditions such as nephrotic syndrome (a kidney disorder causing the body to release too much protein in your urine), blood clotting disorders, cancerous kidney tumors, infections, trauma, or as a complication after a kidney transplant. It has been observed that nearly two-thirds of patients with RVT have it in both kidneys. The left kidney vein is more often impacted because it has more veins compared to the right one. The clot could either extend from the large vein (vena cava) into the smaller veins or it could start in the smaller veins and move towards the main kidney vein.
When a clot forms, it results in severe congestion in the kidney leading to its swelling and engorgement. This causes damage to nephrons, which are the tiny units within the kidney where urine is produced. The damaged nephrons can in turn lead to symptoms like flank pain (pain in your side and back), blood in the urine (hematuria), and reduced urine output.
What Causes Renal Vein Thrombosis?
The most frequent cause of Renal Vein Thrombosis (RVT), a condition where blood clots form in the vein that carries blood away from the kidneys, is a disorder called nephrotic syndrome which can cause the blood to clot too easily. In people with this syndrome, the underlying kidney disease most often linked to RVT is something called membranous nephropathy. This is followed by minimal change disease and membranoproliferative glomerulonephritis, all of which are different types of kidney diseases.
RVT can also be caused by several other factors, both related to the whole body (systemic) and specifically to the kidneys (local).
The systemic causes include:
– Inherited diseases that cause the blood to clot too easily (e.g., antithrombin III deficiency, protein C or S deficiency, factor V Leiden mutation, prothrombin G20210A mutation)
– Antiphospholipid syndrome, an autoimmune disorder
– Rejection of a kidney transplant
– Renal vasculitis, inflammation of kidney blood vessels
– Conditions related to sickle cell anemia
– Systemic lupus erythematosus (SLE), another autoimmune disorder
– Amyloidosis, a condition where abnormal proteins build up in organs
– Diabetic kidney disease
– Pregnancy or taking estrogen therapy
– Behcet syndrome, a rare autoimmune disease
– Severe dehydration or low blood pressure for a long time (especially in newborns)
The local causes include:
– Cancerous kidney tumors, particularly renal cell carcinoma, that grow into the renal veins. This is linked to the formation of a blood clot in 4% to 25% of cases.
– Compression of the renal vein or IVC (the large vein that carries blood from the lower half of the body back to the heart) due to a tumor, lymph nodes, a disease affecting the back of the abdomen, or an aortic aneurysm (a bulge in the main artery of the body)
– An injury to the abdomen or damage during a vein imaging test.
Risk Factors and Frequency for Renal Vein Thrombosis
RVT (Renal Vein Thrombosis) is an illness that often doesn’t show symptoms and may resolve by itself. This makes it hard to determine how common it is in US adults. However, for patients with nephrotic syndrome and membranous nephropathy, it’s estimated that between 5% to 60% of them might have RVT.
RVT can also occur in unborn babies, mainly when there’s a presence of a condition called factor V Leiden. In newborns, it’s one of the main reasons for venous thrombosis and typically happens after severe dehydration or long periods of low blood pressure.
- We don’t have specific data on how often RVT occurs in males or females. But, it seems to be more common in males as it’s often linked to a condition called membranous nephropathy, which affects more males than females (in a 2:1 ratio).
- RVT is more likely to occur as people age, specifically when they have certain kidney diseases like membranous nephropathy. Those in their forties through sixties are particularly at risk.
- There’s no evidence to show that any particular racial or ethnic group is more prone to RVT.
Signs and Symptoms of Renal Vein Thrombosis
Renal vein thrombosis (RVT) is a condition characterized by the formation of a clot in the vein that carries blood away from the kidneys. Symptoms and presentation can vary a lot. For example, chronic RVT can skip noticeable symptoms, though some people might experience peripheral edema, which is swelling caused by excess fluid in the body’s tissues.
Acute renal vein thrombosis usually shows symptoms that are quite different, such as:
- Pain in the side (flank pain)
- Tenderness in the side
- Quick worsening of kidney function
- Increase in protein in urine
- Presence of tiny or visible blood in urine
- Nausea and vomiting
- Fever
If renal vein thrombosis happens after a kidney transplant, it usually occurs within 48 hours of the surgery. Patients may experience abrupt inability to produce urine (anuria) and tenderness over the transplanted kidney.
In young infants and newborns, RVT may lead to a large amount of blood in urine, the presence of a mass (lump) on the side, dehydration, shock, and little to no urine production.
When RVT develops on the left side, it can cause a clot in the gonadal vein (the vein that carries blood from the ovaries in females and the testicles in males). This can lead to pelvic congestion syndrome in females and, in males, it can cause painful swelling of the left testis and an enlargement of the veins within the loose bag of skin that holds the testicles (varicocele).
Testing for Renal Vein Thrombosis
Renal vein thrombosis (RVT), or blood clots in the kidney veins, often begins subtly and without obvious symptoms. Frequently, RVT is found unintentionally during an imaging procedure carried out for another reason.
The surest way to determine whether RVT is present is through a procedure known as renal venography. Besides being a diagnostic tool, it can also be used therapeutically. Today, however, this method is rarely used, as other less invasive tests are available.
Renal ultrasound is a safe, non-invasive way to check for RVT, but it might not always be detailed enough to make a definitive diagnosis. In an ultrasound, an enlarged or high-echogenic (bright in appearance on an ultrasound image) kidney could be seen in around 90% of patients in the early stages of acute RVT. If the ultrasound results are unclear, additional methods, such as Color Doppler or contrast-enhanced ultrasonography, may give better results.
Computed tomography (CT) angiography is generally the preferred test for diagnosing RVT. This method can visualize a clot in the kidney veins, and occasionally in the vena cava, a large vein carrying deoxygenated blood into the heart. CT angiography is almost 100% accurate.
In cases where radiation or intravenous (IV) contrast usage needs to be avoided, contrast-enhanced magnetic resonance venography (3D-CE-MRV) is a great alternative. This technique is just as accurate as a CT scan and can detect not just RVT, but also kidney cell cancer.
As for blood tests, there aren’t any dedicated ones for detecting RVT. Any necessary tests would usually be specific to the underlying cause of the clot, such as tests for nephrotic syndrome (a kidney disorder causing your body to excrete too much protein in your urine) or a pre-existing hypercoagulable state (a condition which increases your risk of blood clots).
Treatment Options for Renal Vein Thrombosis
Renal vein thrombosis (RVT) is usually a consequence of an underlying kidney disease rather than being the cause of the disease itself. The primary strategy is to treat the underlying disease, which is often nephrotic syndrome (a kidney condition that causes the body to expel too much protein in your urine), and to support the functioning of the kidney.
While there aren’t any specific studies to evaluate the effectiveness of blood thinners in asymptomatic RVT (when one doesn’t have any symptoms), it’s generally suggested to start them to prevent the blood clot from growing or causing blockages elsewhere. Similarly, people with symptomatic RVT, such as sudden (acute) RVT, should be treated in the same manner as those who have a blockage in the lung (pulmonary embolism) or in a deep vein (deep vein thrombosis). This usually involves starting on certain types of blood thinners and then switching to warfarin, a different kind of blood thinner. Some treatments like direct thrombin inhibitors and factor Xa inhibitors (types of blood thinners) are not recommended for use in nephrotic patients with RVT because they haven’t been studied in these situations.
People with both RVT and pulmonary embolism who cannot take blood thinners for some reason can be effectively treated with the insertion of a filter into a large vein in the body called the inferior vena cava (IVC) located above the kidney (suprarenal). This filter traps the blood clots and prevents them from reaching the lungs. Blood thinners are typically given for 6 to 12 months, but it’s usually recommended to continue as long as the patient has nephrotic syndrome.
Other treatments like systemic fibrinolysis, which breaks down the blood clots, carry a risk of significant life-threatening bleeding and are usually not recommended. Similarly, directly injecting clot-dissolving drugs or performing a procedure to remove the clot (thrombectomy) in people with acute RVT is linked with acute kidney failure. Rarely, surgical removal of the clot can be considered in cases of acute bilateral RVT (clots in both kidneys) and acute renal failure especially if the clot cannot be removed by other means or if clot-dissolving drugs cannot be used.
What else can Renal Vein Thrombosis be?
Acute Renal Vein Thrombosis (RVT) can present with symptoms similar to other conditions, making it tricky to diagnose. These symptoms, specifically pain in the lower back area and blood in the urine, can be mistaken for:
- Renal colic, which is severe pain due to kidney stones
- Pyelonephritis, a kind of kidney infection
- Renal papillary necrosis, a disorder that destroys the kidney tissues
- Renal infarction, which is a blockage of blood flow to the kidneys, usually due to a clot or embolism
- A cyst in the kidney that can occur with adult polycystic kidney disease
- In some rare cases, acute RVT can also be mistakenly ascribed to a tumor thrombus, which is a condition where a tumor actually extends into a vein
Having these possibilities in mind is important for doctors to accurately identify what’s causing these symptoms and administer the right treatment.
What to expect with Renal Vein Thrombosis
The outlook is generally good with treatment for Renal Vein Thrombosis (RVT), which is a blood clot in a vein that carries blood away from the kidneys. However, the potential health risks and death rate associated with RVT often depend on what caused it in the first place.
For instance, if RVT is due to cancer, complications could come from the cancer itself or cause blood clots in other parts of the body such as Deep Vein Thrombosis (DVT, a clot in a deep vein, usually in the legs) or Pulmonary Embolism (PE, a blood clot in the lungs).
According to a study that looked back at patient cases, if nephrotic syndrome (a kidney disorder causing the body to excrete too much protein in the urine) led to RVT, there was a 40% death rate at 6 months among 27 patients. On a positive note, patients who survived seemed to have stable kidney function and a resolution of their nephrotic syndrome.
However, RVT that happens after a kidney transplant usually has a poor prognosis and often leads to the transplant (graft) failing, particularly within the first month after the transplant.
Possible Complications When Diagnosed with Renal Vein Thrombosis
The possible complications of renal problems may include a decrease in kidney function, which could escalate into chronic kidney disease and has the potential to result in end-stage renal disease. Other complications might involve kidney shrinkage, high blood pressure, or the extension of a blood clot or embolism. In women, left-sided kidney vein blood clots could trigger pelvic congestion syndrome. In men, it may cause swelling of the left testis or varicocele, an enlargement of the veins within the loose bag of skin that holds the testicles.
Following a kidney transplant, a condition called Renal Vein Thrombosis (RVT) is not uncommon and typically occurs shortly after the surgery. The occurrence rate is reported between 0.1% to 4.2% of cases. Unfortunately, this complication usually leads to the loss of the new kidney in nearly all cases.
- Decrease in kidney function leading to chronic kidney disease
- Potential for end-stage renal disease
- Kidney shrinkage
- High blood pressure
- Extension of a clot or embolism
- Pelvic congestion syndrome in women
- Swelling of left testis or varicocele in men
- Renal Vein Thrombosis (RVT) after kidney transplant
- Loss of new kidney due to RVT
Preventing Renal Vein Thrombosis
RVT, or Renal Vein Thrombosis, typically doesn’t cause obvious symptoms. However, if patients start feeling pain in their sides, notice blood in their urine, have less urine than usual, or have trouble breathing, they should see a doctor straight away. People who are aware that they have kidney disease, have had a kidney transplant, or are likely to develop blood clots more often than usual, should be extra careful to notice any of these signs.
