|Fig. 1: Ionizing radiation warning symbol. (Source: Wikimedia Commons)|
Acute Radiation Syndrome (ARS) is an immediate illness that results from excessive radiation exposure over a short period of time. The radiation that causes ARS is large in dosage, which means greater than 0.7 Gray (Gy) or 70 rads; penetrates the body and reaches the internal organs; and affects the entire body or at least a great portion of it.  Cellular damage from radiation happens within microseconds of exposure, and the onset of ARS varies from a few hours to weeks. 
ARS typically follows four stages of symptoms. There is the prodromal stage (N-V-D stage), latent stage, manifest illness stage, and recovery or death. Symptoms of the prodromal stage include nausea, vomiting, anorexia, and diarrhea.  In the latent stage, the patient temporally shows no symptoms of illness and seems healthy, which can last for a few hours or up to a few weeks.  Manifest illness stage varies among specific syndromes: hematopoietic, gastrointestinal, or neurovascular. Recovery takes from few weeks up to two years, and patients who do not recover will die within several months.  As the radiation warning symbol in Fig. 1 aims to alert people, exposure to a large source of ionizing radiation can cause lethal outcomes.
The three ARS syndromes, each of which occurs depending on the absorbed doses. The three syndromes are hematopoietic syndrome (or bone marrow syndrome), gastrointestinal syndrome, and the neurovascular syndrome (or cardiovascular/central nervous system syndrome), which are listed in ascending order of absorbed doses.
The hematopoietic syndrome occurs when irradiation of greater than 1 Gy is delivered to the bone marrow, from which it is distributed throughout the body.  Symptoms of hematopoietic syndrome in the manifest illness stage are anorexia, fever, and malaise.  50% of patients exposed to radiation dose of approximately 3 to 4 Gy may die without prompt medical support. 
Patients exposed to higher radiation doses, beginning at 6 to 8 Gy, suffer from gastrointestinal syndrome and hematopoietic syndrome simultaneously.  Symptoms of gastrointestinal syndrome include malaise, anorexia, severe diarrhea, fever, dehydration, and electrolyte imbalance.  At higher doses, approximately above 10 to 12 Gy, patients will die sooner than if they only had bone marrow syndrome. 
The neurovascular syndrome is less clearly defined in terms of the radiation threshold and the mechanism of death, but experiments on animals and a few human radiation accidents show that exposure to 30 to 50 Gy will cause this syndrome.  Patients exposed to this range of radiation suffer from convulsions and coma, and they normally die within three days of exposure. 
© Michelle Bae. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Acute Radiation Syndrome: A Fact Sheet for Physicians," Centers for Disease Control and Prevention, U.S. Department of Health and Human Services, March 2005.
 S. S. Sugarman et al., "The Medical Aspects of Radiation Incidents, 4th Ed.," Oak Ridge Institute for Science and Education, February 2017.
 T. J. Cerveny, T. J. MacVittie, and R. W. Young, "Acute Radiation Syndrome in Humans," in Medical Consequences of Nuclear Warfare, ed. by R. Zajtchuk, T. J. Cerveny and R. J. Walker (U.S. Dept. of the Army, 1989).