Human Research Participant (Human Subject)

A human research participant — the term used in the regulations
is human subject — is a living individual about whom an investigator
conducting research either (1) obtains information or biospecimens through intervention
or interaction, or (2) obtains, uses, studies, analyzes, or generates identifiable
private information or identifiable biospecimens. This is the operational definition
research administrators and IRBs apply to decide whether a study falls under human
subjects protection rules at all — before questions of consent, risk, or review level
even arise.

Operational definition: 45 CFR 46.102(e)

Under the U.S. Common Rule (45 CFR
46), a “human subject” requires all of the following to be true at once:

• A living individual. Research using only records, tissue, or data
  from deceased persons does not meet this definition under the Common Rule (though it
  may still trigger other obligations, e.g. HIPAA for a covered entity’s records).
• Investigator involvement via intervention or interaction, OR access to
  identifiable private information/biospecimens. “Intervention” covers physical
  procedures (venipuncture, an imaging scan) and manipulations of the person or their
  environment done for research purposes; “interaction” covers communication or
  interpersonal contact, including surveys and interviews.
• Identifiability. Information or biospecimens count even without a
  name attached if the investigator can link them back to a specific person — directly,
  or indirectly through a code or key they hold or can readily obtain. This is why coded
  specimens are not automatically exempt; OHRP guidance on coded private information walks
  through exactly when a coding arrangement still makes someone a human subject.

An activity only becomes human subjects research when this definition is met
and the activity separately qualifies as “research” under the Common Rule’s
definition (a systematic investigation designed to develop or contribute to
generalizable knowledge). Meeting one test without the other does not trigger IRB
oversight.

“Human subject” vs. “human participant”: why both terms exist

The two terms are not competing definitions of different things — they describe the
same person from two different vantage points, and institutions use both because two
different bodies of guidance pull in different directions:

• Regulatory language uses “subject.” The Common Rule, FDA
  regulations, and most institutional IRB policy documents use “human subject” because
  that is the defined term in the statute and regulation itself — changing the word in
  an IRB protocol or consent template doesn’t change the legal test being applied.
• Style and reporting guidance increasingly prefers “participant.”
  The APA Publication Manual recommends “participants” for human research
  (reserving “subjects” for animal research and for a narrow set of fields, such as basic
  memory research, where “subjects” remains the entrenched convention), on the grounds
  that “participant” better reflects a person’s agency and active role rather than
  framing them as something research is done to. Many psychology, health, and
  social-science journals follow this convention in manuscript text even while their
  consent forms and IRB paperwork still say “subject,” because that paperwork is bound by
  the regulatory definition above.

For a research administrator, the practical rule is: use “subject” when you are
citing or applying the regulation (protocol forms, IRB correspondence, consent
documentation referencing 45 CFR 46), and follow the target journal’s or funder’s style
guidance — usually “participant” — in manuscript prose, abstracts, and public-facing
study materials. The two words point at the same regulatory category; picking the wrong
register reads as a style error, not a compliance one.

Examples (meets the definition)

• A researcher conducts recorded, semi-structured interviews with hospital nurses
  about workplace stress and analyzes the transcripts. This is interaction plus
  identifiable private information — the nurses are human subjects.
• A study team draws blood from enrolled volunteers to measure a biomarker and links
  each result to a participant ID the team can trace back to a name. This is intervention
  (venipuncture) plus identifiability — the volunteers are human subjects.
• A researcher requests a biospecimen set from a repository along with the key that
  links each specimen’s code to the donor’s identity. Even though the specimens
  themselves carry no name, holding the key makes them identifiable — this still counts
  as human subjects research under OHRP’s coded-information guidance.

Counter-examples (does not meet the definition)

• A researcher analyzes only the medical records of patients who have died. The
  “living individual” requirement is not met, so this falls outside the Common Rule’s
  human subject definition — even though the same activity involving living patients’
  records would clearly meet it.
• A researcher studies publicly released, aggregate statistics from a national
  statistical agency with no individual-level linkage available to the investigator.
  There is no interaction with a living person and no identifiable private information
  obtained, so this is not human subjects research.

Why this matters before consent or review-level questions

Whether a person is a “human subject” is the threshold question — it has to be
answered before an institution decides whether IRB
review is required at all, what level of review applies, or what
informed consent obligations follow.
Getting this determination wrong in either direction has real consequences: treating a
non-human-subjects activity as if it needs IRB review adds unnecessary delay and
paperwork; missing that an activity does meet the definition — a common failure mode
with secondary data analysis, quality-improvement projects that drift into generalizable
research, or specimen repositories with retained keys — creates a real compliance gap
that can jeopardize a publication or an institution’s federalwide assurance.

Related concepts

• Common Rule (45 CFR 46) — the
  regulation that defines and governs human subjects research.
• Belmont Report — the ethical
  principles (respect for persons, beneficence, justice) that the Common Rule’s
  protections implement.
• IRB (Institutional Review
  Board) — the body that reviews research meeting this definition.
• Informed Consent in Research —
  the consent obligations that follow once someone is determined to be a human subject.
• Withdrawal of consent — a
  related participant-rights concept that applies once someone is enrolled.
• Exempt human subjects
  research — categories of human subjects research the Common Rule exempts from full
  IRB review, but does not exempt from meeting this definition in the first place.