Agranulosis is a medical term that refers to the absence of granules in the blood. It may also be known as agranulocytosis, which is a severe decrease in the number of certain white blood cells. Other synonymous terms that are used to describe this condition include leukopenia, pancytopenia, and neutropenia. Leukopenia refers to a low level of white blood cells, while pancytopenia describes a reduction in the number of all blood cells. Neutropenia refers specifically to a decrease in neutrophils, a type of white blood cell that is important for fighting infections. These terms can be used interchangeably depending on the context of the medical condition.