What is venography?
Venography, also called phlebography (FLEB-og-raff-ee) is a rarely-used diagnostic test that produces X-ray images of the veins and blood flow through them. Veins are not normally visible on an X-ray image, so a special dye is injected into your blood to make them stand out.
Venography can identify and locate blood clots in the veins of the legs and lower abdomen in women with suspected deep vein thrombosis (DVT). Venography can also evaluate chronic vein disease and help plan procedures to improve blood flow.
Venography has historically been the “gold standard” test for diagnosing and investigating vein disease. Today, venography has mostly been replaced by duplex ultrasound to examine the health of the veins and look for blood clots. Ultrasound can provide accurate pictures of the veins without the discomfort, injections, and exposure to radiation required during venography.
Some hospitals offer venography tests using a CT scanner or MRI, instead of X-rays, to produce images of the veins; Alternatives to Standard Venography.
Who might have the test?
Because the venogram test is expensive, uncomfortable, and carries some risk, it has mostly been replaced by less invasive imaging tests. However, venography may still be performed in certain difficult cases to get a closer look at the veins.
In women with a suspected DVT, venography is usually performed only after other tests have failed to find the clot. For example, an ultrasound may fail to find a clot, but a positive D-dimer test may indicate there is a clot somewhere. In these cases, venography can be used to try to locate a clot the ultrasound may have missed.
In women with a suspected pulmonary embolism (blood clot that formed in the veins and broke off to become lodged in a lung artery), CT venography may be added to the standard CT angiogram to try to find the source of the clot. However, there is controversy concerning whether the benefit of finding vein clots in these women is worth the extra radiation exposure.
In women with chronic vein disease, a venogram may occasionally be requested to provide more detailed pictures of the veins, helping to plan a procedure to treat vein disease. However, in most cases an ultrasound test is accurate enough to diagnose chronic vein disease and plan treatments.
Venography is still the test of choice to visualize the veins in women with congenital (in-born) defects in the formation of the veins, and to plan treatment for these conditions.
How do I prepare for the test?
Before the test, you will need to remove all clothing and jewelry and put on a hospital gown. You will be asked about your medical history and given blood-thinning drugs to prevent clots during the procedure. You may be instructed not to eat or drink in the 4 to 8 hours before the procedure.
Before you have the venogram, be sure your doctor knows if you:
- Are allergic to any medications
- Are allergic to the dye used in the test
- Have ever had a serious allergic reaction (anaphylaxis) to any substance
- Have diabetes, especially if you are taking the drug metformin (Glucophage)
- Have a history of bleeding problems or are taking blood-thinning medicines
- Have a history of kidney problems
- Have asthma
- Are pregnant (the radiation and dye used during the test may harm the fetus, so discuss the risks and benefits of the test with your doctor)
- Are breastfeeding (you should not resume doing so until the dye has been cleared from your body, 24 to 48 hours)
Talk to your doctor about any medications or dietary supplements that you are taking because they may affect the accuracy of the test. You may have to stop taking or reduce the dosage of certain medications, particularly blood-thinning medications (e.g., aspirin or warfarin).
What happens during the test?
The venogram test takes place in a specialized room in the hospital. You will lie on a tilting x-ray table and be secured in place with safety straps.
An intravenous (IV) line used to inject the contrast dye during the test will be inserted into a vein (usually on the top of your foot, but sometimes near your groin or on the top of your hand). The injection site will be shaved and disinfected, and you may receive a mild anesthetic cream to make the IV insertion more comfortable. You will feel a sharp pinch as the intravenous line is inserted, but alert the radiologist if there is any further pain.
In some cases, a long thin tube called a catheter will be inserted into a vein in your groin and guided through the veins to inject the dye directly where it is needed. This is done during a venogram to investigate chronic vein disease and see if problems with the veins are causing blood to pool in the legs.
You may experience a warm, flushed sensation as the dye is injected, and a metallic taste in your mouth. After the dye in injected, an X-ray imaging machine will take a series of pictures of the veins in your calf, knee, thigh, and pelvis. Images will be taken from different angles to get a better view of the veins. The table you are lying on may be tilted to a 45 degree angle so that your weight is resting on the unaffected leg, and the leg that is being examined is free. The doctor may also tie an elastic band (tourniquet) just above the knee or around the ankle so that the contrast dye is forced into the deep veins.
When the test is complete, your arm or leg will be elevated and doctors may inject a sterile saline (salt water) solution through the intravenous line to help flush out the dye. You may also receive a blood thinner to prevent blood clots from forming in the veins.
The venography test usually takes 30 to 45 minutes.
What happens after the test?
You should be sure to drink plenty of fluids after the test to help flush the dye from your system. You will stay in the recovery area for at least an hour to ensure the injection site has stopped bleeding and to watch for any signs of an allergic reaction to the dye used in the test. If you had a venogram test that involved the use of a catheter to inject the dye, you will have to stay for 4 to 6 hours to make sure the incision is healing properly, and may receive other special instructions.
Tenderness and bruising at the injection site are normal. Tell the nurse or doctor immediately if you develop a fever, or if the injection site begins bleeding or shows signs of infection such as pain, swelling, warmth, or redness.
What are the risks of the test?
Allergic reaction to the dye used in the venogram test occurs in less than 5% of cases. Other risks of the test include infection at the puncture site and damage to the veins from the catheter used to inject the dye. Very rarely, dye injection may cause blood clots to form in the vein, and squeezing of the calf during the venography test can cause a clot to break loose from the veins and travel to the lungs, causing a potentially deadly pulmonary embolism.
Because X-rays are used to produce an image of the veins and the blood flow through them, the venogram test involves some exposure to radiation. Technicians are trained to minimize your radiation exposure, and the amount of radiation you are exposed to during diagnostic tests is considered safe. If you are concerned about radiation exposure, talk to your doctor about the risks and benefits of the test.
What do the results mean?
In a person with normal veins, the dye will be quickly and evenly distributed through all the veins. The veins themselves will appear straight and not twisted, and no enlarged veins or blood clots will be visible.
Dye that does not penetrate into an area in the middle of a vein, or areas where blood flow stops suddenly, can indicate the presence of a blood clot. Veins that are enlarged or twisted are evidence of chronic vein disease.
How does venography compare with other tests to diagnose vein disease?
The contrast venogram test is considered the “gold standard” test for looking at the anatomy of the veins and detecting chronic vein disease and blood clots. However, because of the risks and costs of the test, it has mostly been replaced by ultrasound as an imaging test for diagnosing blood clots in the veins and chronic vein disease.
|Imaging Tests for Vein Disease|
|Test||Radiation?||Injected Dye?||Invasive?||Time||Other Considerations|
|Ultrasound||No||No||No||30 min||Less accurate in lower legs and pelvis|
|Venography||Yes||Yes||Yes||30 to 45 min||Most accurate but carries risks|
Compared with venography, ultrasound is 95% accurate at diagnosing DVT, without the risks and discomfort of the venogram test.
Are there any alternatives to standard venography?
Some X-ray departments use a CT scanner or MRI machine, rather than X-rays, to produce images of the veins during a venogram test. Although accurate, these tests are not widely available and will only be used after other tests to diagnose vein disease, such as an ultrasound, did not provide enough information.
CT venography uses a CT scanner and an injected dye to produce images of the veins. It is similar to a CT angiogram, except that it produces images of the veins rather than the arteries.
The CT venogram test is rarely done because it is no more accurate than an ultrasound test for diagnosing blood clots and other vein problems, and it takes longer to perform and requires a dye injection and exposure to radiation. A CT venogram is only performed after an ultrasound test did not produce definitive results, or in difficult diagnostic situations like suspected clots in the pelvis that were not visible on the ultrasound scan.
In women with a suspected pulmonary embolism (a blood clot that formed in the veins and broke off to become lodged in a lung artery), a CT venogram may be performed to look for the source of the clot. This is because a CT angiogram is often the first test used to diagnose a pulmonary embolism, and it takes only a few minutes at the end of the test to add a CT venogram. However, it is not clear whether the extra radiation dose required to perform the venogram is worth the risk. In women who have already had an ultrasound to look for blood clots in the veins, the benefits of the CT venogram are not worth the extra risk.
An MR venogram is a diagnostic test that combines magnetic resonance imaging (MRI) with an injected dye to highlight the veins. It is similar to an MR angiogram test, except that it produces pictures of the veins instead of the arteries.
An MR venogram is about 95% accurate compared to a standard venogram for diagnosing DVT in the legs. However, the test is rarely used because it is expensive, is not widely available, and is no more accurate than an ultrasound test for diagnosing DVT and vein disease. In rare cases, an MR venogram may be used as an alternative to a CT venogram in women who have kidney problems or who are allergic to the iodine dye used in the CT venogram.