# Harm scale

> A harm scale ranks how much harm an event caused, from none up to death. No scale is universal. Common ones are the NCC MERP index and the CMS grid.

Source: https://incidentkit.ai/glossary/harm-scale · Updated Oct 5, 2026

Also known as: harm classification, severity scale, harm index

## Common harm scales

A harm scale lets staff rate every event the same way. Pick one scale per event type and define each level in your policy.

| Scale | Levels | Used for |
| --- | --- | --- |
| NCC MERP index | A to I (2001 wording): could cause error; error did not reach the patient; reached with no harm; needed monitoring; short-term harm; hospital stay; permanent harm; life-saving help; death | Medication errors. HHS OIG adapted it for hospital adverse events. |
| CMS scope and severity grid | Four severity levels crossed with isolated, pattern or widespread scope, giving A to L | Nursing home survey findings |
| Joint Commission harm terms | Severe harm: a life-threatening injury needing constant monitoring, surgery or treatment. Permanent harm: harm that permanently changes the patient's usual health. | The sentinel event definition |

## Using a scale

The harm level usually sets how far an event escalates. Death, severe harm or permanent harm brings a full analysis under Joint Commission policy. CMS uses immediate jeopardy (a serious, urgent danger) only when serious harm or death has happened or is likely.

Mix-up: a harm level describes the result, not fault. The same error can land at other levels in other patients. Rate the result, then study the cause on its own.

## Frequently asked questions

### Which harm scale should we use?

Use the one your regulator or accreditor uses for that event type, mapped to your own levels. IHI uses a modified NCC MERP index (HHS OIG).

### What is the NCC MERP index?

A nine-category index, A to I, that sorts medication errors by result, from no harm to death. NCC MERP revised it in November 2022.

### Does the harm level decide how deep the investigation goes?

Often. Higher levels bring a formal root cause analysis and leader review. The Joint Commission requires a full analysis for death, severe harm or permanent harm.

## Sources

- [HHS OIG: Adverse Events in Hospitals: National Incidence Among Medicare Beneficiaries (OEI-06-09-00090, November 2010)](https://oig.hhs.gov/oei/reports/oei-06-09-00090.pdf)
- [NCC MERP: Index for categorizing medication errors](https://www.nccmerp.org/types-medication-errors)
- [CMS State Operations Manual, Chapter 7: Survey and Enforcement Process for Skilled Nursing Facilities and Nursing Facilities](https://www.cms.gov/Regulations-and-Guidance/Guidance/Manuals/downloads/som107c07pdf.pdf)
- [Joint Commission: Sentinel Event Policy (SE chapter), Comprehensive Accreditation Manual, Update 1, July 2026](https://www.jointcommission.org/-/media/tjc/documents/resources/patient-safety-topics/sentinel-event/camncc_20_se_all_current.pdf)
- [CMS State Operations Manual, Appendix Q: Core Guidelines for Determining Immediate Jeopardy](https://www.cms.gov/Regulations-and-guidance/Guidance/Manuals/downloads/som107ap_q_immedjeopardy.pdf)

## Related terms

- [Adverse event](https://incidentkit.ai/glossary/adverse-event)
- [Sentinel event](https://incidentkit.ai/glossary/sentinel-event)
- [Medication error](https://incidentkit.ai/glossary/medication-error)
- [Immediate jeopardy](https://incidentkit.ai/glossary/immediate-jeopardy)
- [Near miss](https://incidentkit.ai/glossary/near-miss)

## Related

- [Incident reporting in healthcare: the complete guide](https://incidentkit.ai/guides/incident-reporting-in-healthcare)
- [Medication Error Reporting: Steps, Severity and Follow-Up](https://incidentkit.ai/use-cases/medication-error-reporting)
- [Joint Commission sentinel event policy: definition and RCA](https://incidentkit.ai/compliance/reporting-deadlines/sentinel-events)
- [Incident routing and escalation by severity](https://incidentkit.ai/product/routing-and-escalation)
- [Incident investigations and root cause analysis](https://incidentkit.ai/product/investigations)