The Alanine Transaminase (SGPT / ALT) test is a blood test that helps to detect any liver damage or disease. It does so by determining the level of a vital liver enzyme in the blood called alanine transaminase. At normal times, ALT is found inside the liver cells. But in case of liver damage or disease, ALT is released into the bloodstream. This results in higher levels of ALT in the blood, often the first sign of liver damage.