Radiation exposure may cause gastrointestinal, pulmonary, hematologic and central nervous system symptoms and their severity, as well as the patient outcome, is directly correlated with the dose of radiation received. Diagnosis is made by clinical findings and patient history.
The term acute radiation syndrome (ARS) is used to describe the onset and progression of symptoms after exposure to ionizing radiation, and the clinical course is divided into four phases  :
Physicians must be careful when interpreting symptoms, as gastrointestinal and central nervous system complaints are nonspecific and may arise in a myriad of conditions. For this reason, patient history is the vital component of the diagnostic workup. The detailed information regarding the onset of symptoms, potential exposure to radioactive substances at the workplace, as well as presence of similar findings in other coworkers is vital in making a presumptive diagnosis . The use of a Geiger-Muller probe attached to a Geiger counter to inspect patients for contamination is pivotal for confirming radiation exposure, and the entire body should be examined . External contamination is performed by surveying the skin, while internal contamination requires sampling of the ears, the mouth, as well as urine, feces and vomit . Laboratory studies should include complete blood counts (CBC) performed on a daily basis after admission, with a particular emphasis on total lymphocyte count, which is considered to be one of the most valid indicators of the dose of radiation received . If a total lymphocyte count is > 1500/mL, the radiation dose is expected to be around 0.4 Gy, and the chance of survival is very high, whereas counts of < 500/mL indicate exposure to > 4 Gy and carry a poorer prognosis . A lymphocyte count of < 100/mL is universally fatal . In addition to lymphocyte count, serum amylase, and C-reactive protein (CRP) levels should be evaluated, as they are elevated in proportion to the dose received  . In the setting of profound skin changes, procedures such as bone scintigraphy, capillary microscopy and nuclear magnetic resonance imaging should be performed, if possible .