A serious adverse event is any untoward medical occurrence in a trial that results in death, is life-threatening, requires hospitalisation, causes persistent disability, is a congenital anomaly or birth defect, or is another important medical event. Seriousness is about outcome, not about how severe the event feels.
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Serious adverse event
noun · clinical research
An adverse event that, in the view of the investigator or sponsor, results in death, is life-threatening, requires inpatient hospitalisation, causes persistent or significant incapacity, or is a congenital anomaly or birth defect.
Related terms
In short
Explained
An adverse event is any untoward medical occurrence in a participant given a study treatment, whether or not it is thought to be related to the treatment. Most are not serious: a headache, a mild rash. The "serious" label is applied by outcome, using a short list that regulators in the US, EU and elsewhere broadly share. The US wording is in 21 CFR 312.32; ICH guidance and EU rules use very similar criteria, though your protocol and local law decide what applies.
Each criterion is a yes or no question the investigator answers for every adverse event. If any one is yes, the event is an SAE and the expedited reporting process starts. This is why a well-built adverse event form asks the criteria explicitly rather than relying on an overall "serious: yes or no" box.
Death and life-threatening events are the clearest. "Life-threatening" refers to an event in which the participant was at immediate risk of death when it occurred. It does not cover an event that might have caused death if it had been more severe. Hospitalisation counts when it is inpatient admission or prolongs an existing stay; planned admissions for a pre-existing condition, or an emergency department visit without admission, are normally handled according to protocol rules, so check yours.
A persistent or significant incapacity, or substantial disruption of the ability to conduct normal life functions, is serious. So is a congenital anomaly or birth defect in the child of a participant. The catch-all, an important medical event, lets the investigator treat an event as serious when medical judgement says it could jeopardise the participant and need intervention to prevent one of the other outcomes. The regulation gives examples such as allergic bronchospasm needing intensive treatment, blood dyscrasias, or convulsions that do not lead to admission.
A "severe" headache is intense but not serious unless it meets a criterion. A "mild" event that results in hospitalisation is serious. The CTCAE grade captures intensity. Causality says whether the study treatment is a plausible cause, and expectedness says whether the event is already described in the reference safety information. A suspected, unexpected, serious adverse reaction is called a SUSAR in EU terminology.
Event
Pneumonia
CTCAE grade
3
Reporting
The clocks below describe the US IND framework. EU, UK and other regimes have their own timelines, so confirm the rules for each country in the study.
| Step | Who | Typical clock |
|---|---|---|
| Tell the sponsor about the SAE | Investigator | Immediately or as the protocol specifies, often within 24 hours of awareness |
| Unexpected, fatal or life-threatening suspected adverse reaction to FDA | Sponsor | As soon as possible, no later than 7 calendar days after initial receipt |
| Other serious, unexpected suspected adverse reactions to FDA | Sponsor | As soon as possible, no later than 15 calendar days after determining it qualifies |
| Tell the IRB or ethics committee | Investigator or sponsor | As set by the committee and the protocol |
Check the current text of 21 CFR 312.32 and your protocol. The 24-hour investigator window is a common protocol convention, not a universal rule.
Build the adverse event and SAE forms, run sample events through the criteria and check the sign-off flow. Free sandbox with every feature.
In Capture
Capture's eCRF library includes adverse event and AESI forms, and a downloadable SAE report form template with the six seriousness criteria, causality, outcome, action taken and sign-off. Edit checks raise an auto-query when a site enters a value that breaks a rule, and each adverse event row carries its own field-level audit trail with the reason for change. Teams can also compute reporting deadlines with the free SAE deadline calculator.
SAE timeline
SAE reported
Day 0 · 09:12
Safety alert acknowledged
Medical monitor · 09:40
Site staff attestation
Study coordinator · 11:05
AE sign-off (PI / Sub-I)
Awaiting signature
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A quick decision aid to walk through the criteria for an example event. It does not replace the investigator's judgement or the protocol.
Seriousness: SERIOUS Criteria met: Requires inpatient hospitalisation or prolongs an existing one Severity (intensity): moderate Causality: related / reasonable possibility Expectedness: unexpected Outcome of this tool: Serious, unexpected, suspected related (SUSAR candidate) Decision aid only: the investigator and sponsor medical assessment governs.
Decision aid, not validated software and not a regulatory determination. Seriousness is a regulatory classification based on outcome (ICH E2A, 21 CFR 312.32). It is separate from severity, causality and expectedness. The investigator and the sponsor's medical reviewer make the assessment, using the protocol and the reference safety information in force. Nothing is stored or sent: the answers stay in your browser.
An adverse event that, in the view of the investigator or sponsor, results in death, is life-threatening, requires inpatient hospitalisation or prolongs it, causes persistent or significant incapacity, or is a congenital anomaly or birth defect. Important medical events can also qualify.
An adverse event is any untoward medical occurrence in a participant. It is serious only if it meets at least one of the seriousness criteria. Most adverse events are not serious.
No. Severity describes intensity, for example by CTCAE grade. Seriousness is based on outcome. A severe event may be non-serious, and a mild one can be serious if it leads to hospitalisation.
The participant was at immediate risk of death when the event occurred. It does not apply to an event that might have been fatal had it been more severe.
Investigators report to the sponsor immediately or as the protocol states. Under US IND rules, sponsors report unexpected fatal or life-threatening suspected adverse reactions to FDA within 7 calendar days of initial receipt, and other serious unexpected suspected adverse reactions within 15 calendar days. Other regions differ.
Inpatient admission or prolongation of an admission meets the criterion. Planned admissions for a pre-existing condition and some emergency visits are often excluded by protocol, so check how your protocol treats them.
A suspected unexpected serious adverse reaction: serious, thought to be related to the study treatment, and not described in the reference safety information. It triggers expedited reporting to regulators.
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