| Criteria | Coma | Brain Death | Remarks |
| Definition | A deep state of prolonged unconsciousness with potential for recovery | Irreversible loss of all brain function, including brainstem | Coma may be temporary; brain death is legally and medically considered death |
| Brain Activity | Some residual brain activity present on EEG | Complete absence of brain activity on EEG | EEG can help distinguish between coma and brain death |
| Brainstem Reflexes | May be preserved or partially impaired | All brainstem reflexes are absent | Brainstem testing is critical in brain death diagnosis |
| Spontaneous Breathing | Often requires ventilatory support but may show respiratory effort | No spontaneous breathing; patient is apneic | Apnea test confirms absence of brainstem respiratory drive |
| Response to Stimuli | No purposeful response but may have non-reflexive movement | No response to any external stimuli, including pain | Reflexive posturing in coma does not indicate consciousness |
| Recovery Potential | Variable; may improve with treatment and time | None; considered biologically and legally dead | Coma outcomes depend on cause, duration, and treatment |
| Diagnosis | Clinical assessment, imaging, EEG, and neurologic monitoring | Strict protocols including neurologic exam, apnea test, confirmatory tests | Brain death requires rigorous, repeated testing by qualified physicians |
| Legal Status | Not considered dead; life-sustaining treatment is often continued | Legally recognized as death in most countries | Organ donation is typically only considered after declaration of brain death |
| Organ Donation Eligibility | Not eligible unless progresses to brain death or cardiac death | Eligible for organ donation if criteria are met and consent is given | Brain death enables organ donation while circulation is still maintained artificially |
