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This terminology helps to define Adverse Events and then to decide their severity using a grading system.
The terminology can be used in clinical trials as described below. It can also be used to provide a standardised comprehensive assessment of medical occurrences in observational studies, audits and quality improvement projects.
PDF file - MFAET Version 1.1 with instructions for use -
Excel file Version 1.1 including MedDRA numerical codes -
AEs in clinical trials
During clinical trials, Adverse Events are reviewed to determine:
(1) whether the AE meets the definition of ‘serious’2:
- Results in death
- Is life-threatening
- Requires inpatient hospitalisation or results in prolongation of existing hospitalisation
- Results in persistent or significant disability/incapacity
- Is a congenital anomaly/birth defect
- Is a medically important event or reaction
(2) whether it is possibly, probably or definitely related to the intervention (i.e. is a reaction). The event is then classified as:
Serious | Reaction | |
Adverse event (AE) | No | No |
Adverse reaction (AR) | No | Yes |
Serious adverse event (SAE) | Yes | No |
Serious adverse reaction (SAR) | Yes | Yes |
Grading Adverse Events
AEs are graded from 1 to 5:
Grade 1: mild
Grade 2: moderate
Grade 3: severe or medically significant
Grade 4: life-threatening
Grade 5: death
If an AE fulfils the criteria for more than one grade of severity, the highest applicable grade should be used. Grading the severity of AEs provides additional safety information. It does not replace the regulatory requirements for AE assessment described above.