An alanine aminotransferase (ALT) test measures the level of ALT enzyme in your blood. ALT is an enzyme produced by liver cells. It helps the body metabolize proteins. If the liver is damaged or not functioning properly, ALT is released into the blood. This causes ALT levels to increase. The alanine aminotransferase (ALT) test is used to evaluate liver function. The test is also known as a serum glutamate pyruvate transaminase (SGPT) test or alanine transaminase test.