Agranulocytosis, also known as Agranulosis or Granulopenia, is an acute condition involving a severe and dangerous leukopenia, most commonly of neutrophils causing a neutropenia in the circulating blood. It represents a severe lack of one major class of infection-fighting white blood cells. People with this condition are at very high risk of serious infections due to their suppressed immune system. In agranulocytosis, the concentration of granulocytes drops below 100 cells/mm³ of blood, which is less than 5% of the normal value. Agranulocytosis is more severe than granulocytopenia and may involve more sub-types of white blood cells than neutropenia.