Blood tests are done to determine how well your liver works. A prothrombin time test measures how long it takes your blood to clot. With acute liver failure, blood doesn't clot as quickly as it should. Your doctor may recommend an ultrasound exam to look at your liver. Such testing may show liver damage and help your doctor determine the cause of your liver problems. Your doctor may also recommend abdominal computerized tomography (CT) scanning or magnetic resonance imaging (MRI) to look at your liver and blood vessels. These tests can look for certain causes of acute liver failure, such as Budd-Chiari syndrome or tumors. They may be used if your doctor suspects a problem and ultrasound testing is negative. Your doctor may recommend removing a small piece of liver tissue (liver biopsy). Doing so may help your doctor understand why your liver is failing. Since people with acute liver failure are at risk of bleeding during biopsy, the doctor may perform a transjugular liver biopsy. The doctor makes a tiny incision on the right side of your neck, and then passes a thin tube (catheter) into a neck vein, through your heart and into a vein exiting your liver. Your doctor then inserts a needle through the catheter and retrieves a sample of liver tissue.