CTCAE is a standard list of adverse event terms, published by the US National Cancer Institute, with a severity grade from 1 to 5 defined for each term. Trials use it so that investigators grade the same event the same way.
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Common Terminology Criteria for Adverse Events
noun · clinical research
A descriptive terminology and grading scale from the US National Cancer Institute, used to report the severity of adverse events from grade 1 to grade 5.
Related terms
In short
Explained
Left to themselves, two investigators may describe the same nausea as "bad" or "tolerable", and a sponsor cannot compare safety across sites on that basis. CTCAE solves this by defining, for each named adverse event, what each grade means in clinical terms. Diarrhoea, for example, is graded by how many stools per day exceed baseline and whether hospitalisation or urgent intervention is needed; a laboratory abnormality is graded against thresholds. The investigator picks the term, then picks the grade whose description fits.
The criteria were developed by the NCI for cancer therapy trials, where treatments are often toxic by design and the dose is adjusted to toxicity. According to NCI, version 6.0 was developed in collaboration with NCI's Division of Cancer Prevention and FDA, and was aimed at problems such as grading adverse events in people whose baseline laboratory values are already abnormal, describing events linked to immunotherapies, and categorising cardiac events. A correction (errata) was issued in January 2026, so teams should download the current files rather than rely on an old copy.
Each term has a description for grades 1 to 5, although not every term uses all five. In general terms, grade 1 is mild, grade 2 is moderate, grade 3 is severe or medically significant but not immediately life-threatening, grade 4 is life-threatening with urgent intervention indicated, and grade 5 is death related to the adverse event. Treat this as orientation only: the wording for the specific term in the CTCAE file is what counts, and some terms have no grade 4 or 5 at all.
Regulators define a serious adverse event by outcome: death, life-threatening event, hospitalisation, persistent incapacity, congenital anomaly, or an important medical event. CTCAE grades describe intensity. A grade 3 laboratory abnormality found on a routine blood test may be non-serious, while a grade 2 event that puts the participant in hospital is serious. Good eCRF design therefore has separate fields for CTCAE grade and for each seriousness criterion. The seriousness decision tree walks through the second question.
CTCAE is clinician-assigned. A companion NCI item library, PRO-CTCAE, lets participants report the frequency, severity and interference of symptomatic adverse events themselves; a PRO-CTCAE eCRF template is available. Comparing clinician grades with patient reports is a common way to find under-reported symptoms.
| CTCAE grade | Serious? | Why | |
|---|---|---|---|
| Neutropenia, grade 3, found on routine bloods | 3 | No | No seriousness criterion met |
| Nausea, grade 2, admitted for IV fluids | 2 | Yes | Hospitalisation |
| Rash, grade 1 | 1 | No | Mild, no criterion met |
| Event with fatal outcome | 5 | Yes | Death |
In practice
The mechanics are the same in every trial that specifies CTCAE.
Choose the closest term in the version named in the protocol. If nothing fits, record the event in free text and, if the protocol allows, grade it by the generic mild to fatal descriptions.
Read the descriptions for the term, not just the number. Grade at the worst severity reached during the event, and say so in the protocol or completion guidelines so every site does the same.
Grades can change over time. Sponsors often collect each change in grade as a new line, or the maximum grade with start and stop dates, depending on the analysis plan.
Complete the seriousness criteria and the relationship to the study treatment. These drive expedited reporting, not the grade.
Dose holds, reductions and stopping rules are usually tied to specific grades. A grade recorded wrongly can trigger or miss a dose change.
In Capture
In Capture you can build an adverse event eCRF that includes a grade field with the choices your protocol names, alongside seriousness, causality, action taken and outcome. Edit checks raise an auto-query when a site enters a value that breaks a rule, every change is recorded in a field-level audit trail, and the repeating adverse event rows each carry their own history. Start from the adverse event template rather than a blank form.
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Causality is required because the event is serious.
Create the form, test the skip logic and edit checks with sample data, and keep every change audited. The sandbox is free with every feature.
Try it
A quick reference for looking up a term and its grade descriptions. Always confirm against the CTCAE version your protocol names.
| Grade 1 | <LLN - 1500/mm3; <LLN - 1.5 x 10e9 /L |
|---|---|
| Grade 2 | <1500 - 1000/mm3; <1.5 - 1.0 x 10e9 /L |
| Grade 3 | <1000 - 500/mm3; <1.0 - 0.5 x 10e9 /L |
| Grade 4 | <500/mm3; <0.5 x 10e9 /L |
| Grade 5 | – (grade not available) |
Source: NCI CTCAE v5.0, published 27 November 2017 (ctcae-v5.0.xlsx, dctd.cancer.gov).
*Instrumental ADL: preparing meals, shopping for groceries or clothes, using the telephone, managing money, etc. **Self care ADL: bathing, dressing and undressing, feeding self, using the toilet, taking medications, and not bedridden. A semicolon means “or” within a grade; a dash means the grade is not available for that term. LLN and ULN are the lower and upper limits of normal.
Reference only: 34 common terms, not the full CTCAE, and not validated software. Use the version your protocol names. Grading, seriousness and causality are the investigator's clinical judgement; always check the official NCI document.
Checklist
Write "CTCAE v6.0" or the version you choose, and the date of any errata you apply. Do not change version mid-study without an amendment.
Use a single-choice grade question and distinct yes or no questions for each seriousness criterion.
Say whether to record maximum grade or each change in grade, and how to grade events with no matching term.
Queries for grade 5 without a death date, or a serious event without a seriousness criterion ticked.
List which grades trigger a hold, reduction or discontinuation so reviewers can check them.
Decide which tables will be produced by grade and how events graded 3 or higher are listed.
Common Terminology Criteria for Adverse Events. It is published by the US National Cancer Institute and provides standard adverse event terms with a severity grade for each.
Version 6.0, with a publication date of 22 July 2025 in NCI's document. Version 5.0 is the previous version. An errata was reported in January 2026, so download the current files and follow the version your protocol names.
Broadly, 1 is mild, 2 is moderate, 3 is severe or medically significant, 4 is life-threatening and 5 is death related to the event. The exact description differs for every term, so use the CTCAE document for the term in question.
No. Grade describes intensity; seriousness is defined by outcomes such as hospitalisation or death. A grade 3 event may be non-serious, and a lower-grade event can be serious.
It was developed for cancer therapy trials and is most common there, but other trials sometimes use it as a ready-made grading scale. Many non-oncology protocols use mild, moderate and severe instead.
A companion NCI item library that lets participants report the frequency, severity and interference of symptomatic adverse events in their own words, alongside clinician-assigned CTCAE grades.
Yes. Add a single-choice grade field to the adverse event form, with edit checks that flag inconsistencies, and keep seriousness and causality in their own fields.
Keep exploring
Serious adverse event (SAE)
Seriousness is a different question.
CTCAE grade lookup
Look up a term and its grades.
Adverse event eCRF template
Start from a ready form.
PRO-CTCAE eCRF template
Patient-reported symptom AEs.
Adverse event reporting software
Capture and report AEs.
AE seriousness decision tree
Serious or not?
Build the form, test the checks, review the audit trail. No credit card.