Airman 1st Class Sabrina Huerta, 779th Medical Group Medical laboratory technician, performs a Prothrombin Time/Partial Thromboplastin Time (PT/PTT) test Jan.31, 2013 at Joint Base Andrews, Md. This test measures how quickly a blood clot forms and is used to prevent heart attacks and blood clots. (U.S. Air Force photo/Airman 1st Class Erin O’Shea)