context: Your blood's ability to clot helps keep you alive. Without it, every shaving nick and paper cut could turn into a medical emergency. But clotting can be a serious problem when it happens where it shouldn't, like in your veins, where a clot can cut off your blood flow. That's called a venous thromboembolism ( VTE). VTEs are dangerous, but they're treatable -- and there's a lot you can do to lower the odds you'll get one. You may have never heard of a VTE before, but they're common. There are two types, which are set apart by where they are in your body. Deep vein thrombosis ( DVT). As the name suggests, it develops deep in your veins, usually in the legs. You can get one in your arm, though. When this happens, your doctor may call it an upper-extremity DVT. It can cut off the flow of blood. DVTs can cause pain, swelling, redness, and warmth near the blocked vein. Pulmonary embolism ( PE). This is more serious than a DVT. It usually happens when a DVT breaks loose and travels to your lungs. A pulmonary embolism is a life-threatening emergency. It can make it hard to breathe and cause a fast heart rate, chest pain, and dizziness. It can also cause you to become unconscious. DVT symptoms include: Pain or tenderness in your arm or leg, usually in the thigh or calf Swollen leg or arm Skin that's red or warm to the touch Red streaks on the skin With a pulmonary embolism, you could notice: Shortness of breath you can't explain Fast breathing Chest pain under your rib cage that can get worse when you take a deep breath Rapid heart rate Feeling lightheaded or passing out VTEs can happen if your blood flow changes or slows down somewhere in your body. Lots of things can cause that, like some diseases, medical treatments, and long airplane flights where your legs are stuck in the same position. Things that raise your chances of having a VTE include: Medical treatments. Your odds for a VTE go up if you're in the hospital for a while, get surgery (especially on your knees or hips), or have cancer treatments like chemotherapy. Health conditions. Your VTE risk is higher if you have cancer, lupus or other immune problems, health conditions that make the blood thicker, or you're obese. Medications. Hormone replacement therapy and birth control pills can make it more likely you'll get a VTE. Your chances of a VTE also go up if you had an earlier VTE, stay in the same position for a long time, have a family history of blood clots, smoke, are pregnant, or you're over 60. To rule out VTE, your doctor may perform this test: D-dimer: This looks for levels of D-dimer, a substance that's in your blood when you have a clot. If the test is normal, meaning your levels aren't high and there's no clot, you might not need any more tests. If you do need more tests for DVT, you could get: Duplex ultrasound. This painless imaging test doesn't have radiation the way an X-ray does. It uses sound waves to create a picture of your legs. The doctor spreads warm gel on your skin, then rubs a wand over the area where she thinks the clot is. The wand sends sound waves into your body. The echoes go to a computer, which makes pictures of your blood vessels and sometimes the blood clots. A radiologist or someone who's specially trained has to look at the images to explain what's going on. For a pulmonary embolism, you might also get: Pulse oximetry: This is often the first test. The doctor will put a sensor on the end of your finger that measures the level of oxygen in your blood. A low level can mean a clot is preventing your blood from absorbing oxygen. Arterial blood gas: The doctor takes blood from an artery to test the level of oxygen in it. Chest X-ray: This test helps rule out a clot. They don't show up on X-rays, but other conditions, like pneumonia or fluid in the lungs, do. Ventilation perfusion ( V/ Q) scan: Doctors use this imaging test to check your lungs for air flow (ventilation, or V) and blood flow (perfusion, or Q). Spiral computed tomography: This is a special version of a CT scan in which the scanner rotates to create a cross-section view of your lungs. Pulmonary angiogram: If other imaging tests aren't clear, doctors will use this test. Unlike the others, this test is invasive -- the doctor will put a catheter into a vein and guide it to the veins and arteries around your heart. He'll use it to inject a dye that shows up on an X-ray. This helps him see if there's a clot in your lungs. Echocardiogram: This ultrasound of the heart can help the doctor see areas that aren't working the way they should. This test doesn't diagnose PE, but it can show strain on the right side of your heart that results from PE. If you have a VTE, you need to get it treated right away. Your doctor may talk to you about treatments like these: Blood thinners. These drugs don't break up the clot, but they can stop it from getting bigger so your body has time to break it down on its own. They include heparin, low-molecular-weight heparin, apixaban ( Eliquis), edoxaban ( Savaysa), rivaroxaban ( Xarelto), and warfarin ( Coumadin). Clot-busting drugs. These medicines are injections that can break up your clot. They include drugs like t PA (tissue plasminogen activator). Surgery. In some cases, your doctor may need to put a special filter into a vein, which can stop any future clots from getting to your lungs. Sometimes, people need surgery to remove a clot. Even after you recover from a VTE and you're out of the hospital, you'll probably still need treatment with blood thinners for at least 3 months. That's because your chances of having another VTE will be higher for a while. There's a lot you and your doctors can do to cut your odds of getting a VTE. Here's the most important thing: If you need to stay overnight in a hospital, ask your health care team about VTEs before you check in. Almost 2 out of 3 VTEs happen because of hospital visits. But if you get the right preventive treatment in the hospital, your risk can go way down. If your health care team thinks you have a higher risk for a VTE -- based on your medical history, health, and the type of treatment you're getting -- you may need: Blood thinners Compression stockings (special tight socks) that help with blood flow Intermittent pneumatic compression devices, which are kind of like blood pressure cuffs that automatically squeeze your legs to keep blood flowing You may also need to get out of bed and walk around as soon as you can after treatment. If you've had a VTE in the past, talk to your doctor about whether you need regular treatment to lower your chances of getting another. There are also things that everyone can do to lower their chances of a VTE: Get regular exercise. Be at a healthy weight. If you smoke, quit. And when you're traveling, whether by train, plane, or car: Get up and walk around every 1 to 2 hours. Move around in your seat and stretch your legs often. Drink lots of fluids. Don't smoke before your trip. Don't drink alcohol, since it can dehydrate you. Don't use medicines to make you sleep, so you'll stay awake enough to move around. Ask your doctor if you should take an aspirin before a long plane flight.