Severity, Seriousness and Why They Are Different

Part of Sub-Investigator (SUBI) Training: Adverse Events and Attribution.

About 2 minutes. Free, in your language, no account needed.

Two words that are not synonyms

Severity is how bad it is. Mild, moderate, severe, or a graded scale.

Seriousness is a regulatory definition. It has a fixed list of criteria. Death. A life-threatening event. An admission to hospital, or a longer stay. Lasting or significant disability. A congenital anomaly. Or another important medical event.

They are independent. A mild event can be serious. A severe event can be non-serious.

The classic example

A mild allergic reaction leads to an overnight admission for observation. That is mild and it is serious. Admission is a seriousness criterion.

A severe migraine managed at home is severe and non-serious.

Recording severity in the seriousness field is one of the most common errors in trial safety data. It also changes the reporting clock.

Important medical events

The catch-all criterion is the one people miss. An event may meet none of the listed criteria and still be serious. That happens if it puts the participant at risk, or if treatment was needed to prevent one of the listed outcomes.

A bronchospasm treated successfully in clinic is the standard example. No admission, and serious.

Hospitalization has exclusions

A planned admission for a condition they already had is usually not a seriousness criterion. Neither is a procedure recorded at baseline. The protocol will say.

Do not apply the exclusion to an admission that was brought forward because the participant deteriorated.

Expectedness is a third, separate thing

Expectedness asks one thing. Is the event already listed in the reference safety information, usually the investigator brochure? It is not a judgment about whether you are surprised.

Severity, seriousness, causality and expectedness are four independent judgments.

Get seriousness right first

It drives the clock. A serious event has an expedited reporting timeline, and the clock starts at site awareness.