RnCeus explains that "SEG" refers to mature neutrophils, a type of white blood cell. A blood test that measures SEG is usually trying to determine if the number of neutrophils has increased, a result that suggests the presence of a bacterial infection or an inflammatory process.
Although less common, a reduction in neutrophils can also indicate health problems, says Lab Tests Online. A low neutrophil count may indicate an autoimmune disorder, the presence of an overwhelming infection, a drug reaction or aplastic anemia.
Mercy Medical Center-North Iowa reports that the normal range for SEG in an adult is 35 to 80 percent and 1.6 to 7.1 thousand per microliter.