Incidental vs. Secondary Findings: What’s the Difference?

If Both Are Outside the Research Question, What Makes Them Different?

A researcher sequencing DNA for one purpose notices a potentially important variant associated with an unrelated condition. In another study, researchers deliberately analyze the same genomic data for a predefined set of unrelated but medically actionable variants.

Both situations produce information outside the primary research question. Yet they are not ethically identical. In one case, the researcher encounters the information while doing the planned research. In the other, the researcher deliberately goes looking for it.

That difference is the clearest contemporary distinction between an incidental finding and a secondary finding. Unfortunately, the terminology has not always been used consistently, which explains much of the confusion.

The Difference Is Usually Whether the Finding Was Deliberately Sought

The Intent Behind the Search Separates the Two Concepts

What is an incidental finding?

An incidental finding arises outside the original purpose of a research test, procedure, or analysis and is encountered without researchers deliberately conducting a separate search for that information.

Suppose researchers perform brain imaging to study memory and notice an unexpected abnormality unrelated to memory. Or genomic researchers analyzing genes relevant to one disorder happen to identify a variant associated with another condition. The potentially important information has appeared because of the research procedure, but discovering that particular information was not an additional objective.

This is the core problem addressed when considering what responsibility follows from discovering an incidental finding.

What is a secondary finding?

A secondary finding is also outside the primary target of the test or research question, but there is one crucial difference: someone intentionally searches for it.

The U.S. Presidential Commission for the Study of Bioethical Issues described a secondary finding as an additional result actively sought despite not being the primary target of the test or procedure. Current NIH genomic resources use a similar distinction, describing secondary findings as pathogenic or likely pathogenic variants in medically actionable genes that are directly searched for even though they are unrelated to the primary indication for sequencing.

The same information can be incidental in one study and secondary in another

The classification does not depend only on what the information is. It also depends on why and how researchers identified it.

A pathogenic variant associated with a hereditary cardiac condition could be incidental if it happens to become apparent during analysis for an unrelated research question. The identical variant could be a secondary finding if researchers intentionally screen participants' sequence data for that cardiac gene even though it is unrelated to the study's primary objective.

In other words, “incidental” and “secondary” describe the relationship between the finding and the investigative process, not two inherently different categories of biological information.

Incidental does not mean unforeseeable

This is an important distinction. An incidental finding can be unexpected for a particular participant while still being an anticipated possibility of the research procedure.

The Presidential Commission distinguished between anticipatable incidental findings, whose possible occurrence is known to be associated with a test or procedure, and unanticipatable incidental findings, which could not reasonably have been anticipated given current scientific knowledge.

For example, researchers conducting MRI studies may know that unrelated abnormalities will occasionally appear even though they cannot predict which participant will have one. Such a finding remains incidental because researchers did not deliberately perform the scan to find that abnormality.

Secondary does not mean less important

The word “secondary” refers to the finding's relationship to the primary purpose, not its medical importance. A secondary finding can be more consequential to a participant's health than the result that motivated the original analysis.

This is particularly visible in genomic medicine, where professional recommendations may specify deliberate searches for pathogenic or likely pathogenic variants associated with preventable or treatable conditions. The search is secondary to the original indication, but its potential consequences are not necessarily secondary in any ordinary sense of importance.

Why are the terms sometimes used differently?

Because the vocabulary developed alongside rapidly changing genomic technologies and ethical debates, the literature contains overlapping terminology. Older sources sometimes use “incidental findings” broadly for results unrelated to the original purpose, including results that researchers or clinicians deliberately seek. “Unsolicited findings” is another term encountered in the literature for findings discovered without deliberate searching.

NHGRI's older overview of return of research results, for example, notes that incidental findings have also been called secondary findings. More recent NIH materials distinguish secondary genomic findings by emphasizing that they are directly searched for. The American College of Medical Genetics and Genomics also shifted from describing its recommendations as involving “incidental findings” to the terminology of “secondary findings.”

Why does the distinction matter ethically?

Encountering information and deliberately generating additional information can create different responsibilities. If an important abnormality appears while researchers are performing an already justified procedure, the ethical question becomes how that information should be managed. If researchers propose an additional search unrelated to the study's main question, they must first justify conducting that search.

The latter can introduce additional analytic work, validation requirements, consent considerations, counseling needs, follow-up obligations, and costs. It may also create information that a participant never expected the study to generate.

That is why the distinction leads directly to a separate question: should researchers actively search outside the research question merely because useful information might be found?

One Dataset, Two Very Different Ways to Find the Same Variant

The DNA variant itself could be identical in both scenarios. What changes is the route by which the researchers found it. That difference affects what researchers should have planned, explained during consent, budgeted for, validated, and arranged to communicate.

Where the Terminology Commonly Goes Wrong

Classify the Search Before You Decide How to Manage the Result

When designing a study, ask what analyses are actually part of the research and whether you intend to search deliberately for information unrelated to those aims. This is more useful than waiting until a potentially important result appears and then arguing about terminology.

Classification does not by itself determine whether a finding should be returned. Questions about disclosing unexpected findings to participants, their importance, actionability, uncertainty, and participant preferences still require separate ethical assessment.

Before Calling a Result Incidental or Secondary

Questions About Incidental and Secondary Findings

The Crucial Difference Is Whether You Went Looking for It

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