Physicians perform a series of tests to determine if brain death has occurred. Consideration of the diagnosis is based on the catastrophic injury and the current clinical presentation. Tests are conducted to examine all areas of the brain including the breathing center, confirming that the patient is unable to breathe without mechanical assistance (apnea). Brain death is diagnosed by clinical examinations done by two different physicians, and further confirmed by other tests (apnea or inability to breathe, EEG showing brain silence, blood flow or CT angiography showing no blood entering the brain).

Once brain death has been declared, there is no chance for recovery. The legal time of death is when the final diagnosis of brain death has been documented in the hospital chart. Hospitals typically provide some compassionate time before disconnecting the ventilator after brain death declaration.