Acute radiation sickness occurs to subjects after exposure to internal and external radiation. Major nuclear plant catastrophes are best descriptive of possible situations where high dosage of radiation may come in contact with a human body and develop this disease.
Acute radiation sickness (ARS) or acute radiation syndrome negatively influences all organ systems, especially that of the hematopoietic system. The reason for it is the dependence on stem cells that are primarily affected in a situation of acute radiation exposure. Ionizing radiation causes damage to double-stranded DNA molecules resulting in the loss of proliferative function and damage to affected cells .
Acute radiation sickness expresses itself in three phases: prodromal, latent and manifestation phase.
The prodromal phase includes symptoms of the gastrointestinal (GI) tract such as nausea, vomiting, and diarrhea with consequent fluid, electrolyte loss, and anorexia. Non-specific symptoms like a headache, hypotension, fever, erythema are also present . It is important to differentiate these symptoms from those of GI infections or other pathologies involving this system.
The latent phase is characterized by the discontinuation of symptoms seen in prodromal phase or mild exhibition of them. The duration of this phase is dependent on the dose of radiation certain subject was exposed to .
Manifestation phase follows after latent phase. The manifestation of ARS involves multiple organ systems, firstly that of the hematopoietic system .
More serious complications of severe cases in ARS are accountable for systemic inflammatory response syndrome (SIRS) with following multi-organ failure (MOF) .
It is possible to assess acute radiation sickness with a proposed medical treatment protocols for radiation accident victims (METREPOL). It is convenient in distinguishing affected organ systems based on clinical presentation. The protocol calculates severity and possible damage done to the neurovascular, gastrointestinal, cutaneous and hematopoietic systems. For example, damage to the GI is scored by evaluating the time of onset, severity, the frequency of vomiting or diarrhea  . A score of 1 is given to a patient who does not need acute medical attention and should be referred to an outpatient clinic for further follow ups. A score of 2 is given to a patient who is in high need of professional care. And a score of 3 is given to those who are likely to suffer from multiple organ failures (MOF) and have an overall low risk of survival  .
Blood tests are of paramount importance to control the dynamics of the patient as the hematopoietic system is greatly radiosensitive. To achieve proper care, repeated blood count of granulocytes, platelets, and lymphocytes are needed about every 6 hours for the first 24h and reticulocyte count every 24h . Standard biochemical tests are also necessary. If there is suspicion of radionucleotide ingestion, the analyses of urine and feces will provide appropriate evidence .
Biodosimetry of chromosome aberrations in lymphocytes is useful in determining the possible dose of radiation, as the severity of aberrations strongly correlate to the dosage of radiation given . During biodosimetry, analysis of translocations, dicentrics and chromosome consolidations are sought .
Physical dosimetry is convenient for providing analysis for individual dose taken but is a technique limited in availability. It is also possible to obtain high-quality radiation dosage data from an in vivo electron paramagnetic resonance (EPR) dosimetry that works by evaluating nail or teeth .