What Happens When a Child Participant Reaches the Age of Legal Consent During a Longitudinal Study?

What changes when a child participant becomes legally able to consent?

A 16-year-old enters a five-year longitudinal study with parental permission and the adolescent's assent. Two years later, the participant reaches the legal age at which they can consent to the research for themselves. The study still has questionnaires, interviews, specimen collection, or follow-up visits remaining.

Can the researchers simply continue relying on the parent's original permission?

Generally, no. Under the U.S. HHS framework, the parental-permission and child-assent arrangement used while someone was legally a child does not automatically authorize ongoing research participation once that person becomes legally capable of providing their own consent. If ongoing interactions or interventions continue, legally effective informed consent ordinarily needs to be obtained from the now-adult participant unless an IRB has approved an applicable waiver.

The participant's own consent becomes the relevant authorization

Parental permission does not follow the participant indefinitely

The legal basis for participation changes

While a participant is legally a child for the research involved, enrollment may depend on parental or guardian permission together with the child's assent when assent is required. Once the participant reaches the legal age at which they can consent to the research procedures themselves, that framework changes.

OHRP explains that parental permission and child assent are not equivalent to legally effective informed consent for the now-adult participant. If the research continues to involve interactions or interventions, investigators ordinarily need the participant's own informed consent unless the IRB has approved a waiver under the applicable regulations.

This follows from the basic difference between assent and informed consent. Assent gave the child a meaningful role in the original decision, but it did not prospectively become adult consent on a later birthday.

Do not assume that the relevant age is always 18

“Turning 18” is a convenient shorthand in many U.S. research settings, but the HHS definition of children does not establish 18 as a universal research threshold. Children are persons who have not reached the legal age for consent to the treatments or procedures involved in the research under the applicable law of the jurisdiction where the research is conducted.

The relevant transition therefore depends on applicable law and the research activities involved. In some circumstances, a minor may already have legal authority to consent to particular treatments or procedures before reaching the general age of majority.

Researchers should identify the legally relevant transition point rather than hard-code age 18 into every protocol without checking the applicable rules.

Ongoing interaction or intervention usually makes the answer straightforward

Suppose a participant reaches legal consent age while the study still requires annual interviews, surveys administered directly by the research team, imaging, blood collection, experimental interventions, or other research interactions or interventions.

Under OHRP guidance, investigators should seek and obtain legally effective informed consent from the now-adult participant for these ongoing research activities unless the IRB has waived the requirement.

The parent's earlier permission no longer provides the appropriate authorization for new interactions or interventions once the participant can legally decide for themselves.

The participant should receive an adult consent process, not merely another signature

Obtaining adult consent should not be reduced to asking the participant to sign a new form because the database flagged a birthday.

The participant should receive the information required for informed consent in understandable language and have an opportunity to ask questions and decide whether continued participation is acceptable. Depending on how long the study has been running, circumstances may have changed since the original enrollment.

The researcher may need to explain what has already occurred, what remains, foreseeable risks and potential benefits, confidentiality, relevant alternatives when applicable, whom to contact, and the voluntary nature of continued participation.

The participant can say no even if the parent originally said yes

Once the participant has legal authority to consent, they are not obligated to continue simply because their parent previously permitted enrollment or because they themselves assented as a child.

The adult participant may consent to continue, decline further participation, or withdraw as permitted by the applicable protocol and regulations. Researchers should avoid presenting re-consent as administrative paperwork for a decision that has already been made.

Previously collected data create a separate question

The situation becomes more nuanced when no further interaction or intervention will occur but researchers still possess identifiable private information or identifiable biospecimens collected while the participant was a child.

OHRP has explained that continued use of identifiable information or biospecimens after a participant reaches the legal age of consent remains human-subjects research under the Common Rule. In such circumstances, investigators ordinarily need legally effective consent from the now-adult participant unless the IRB determines that the requirements for waiver of consent are satisfied.

This is one reason the narrower question of whether adult consent must be obtained from participants originally enrolled as children deserves separate treatment.

De-identification can change the regulatory analysis

Under the Common Rule, research involving information or biospecimens that are not identifiable may fall outside the regulatory definition of research involving human subjects, depending on the circumstances.

Consequently, if data or specimens collected during childhood have been irreversibly de-identified before the participant reaches legal consent age and no further interaction or intervention will occur, the re-consent analysis may differ from a study continuing to use identifiable material.

Researchers should not make this determination casually. Whether information or biospecimens are identifiable for regulatory purposes should be evaluated under the applicable rules and IRB procedures.

A waiver may sometimes be possible

OHRP recognizes that obtaining informed consent from every participant who reaches adulthood may sometimes be difficult in long-running research, particularly where contact has ended and only identifiable information or specimens remain.

The IRB may waive informed consent when the applicable requirements of 45 CFR 46.116 are satisfied. For a general waiver under the current Common Rule, these requirements ordinarily include no more than minimal risk, impracticability without the waiver, protection of subjects' rights and welfare, additional considerations when identifiable private information or biospecimens are involved, and provision of additional pertinent information afterward when appropriate.

The existence of a possible waiver does not mean investigators can simply decide that re-contacting participants is inconvenient.

Longitudinal protocols should anticipate the transition from the beginning

If a study enrolls children and follows them for several years, some participants reaching legal consent age is predictable rather than exceptional.

The protocol should explain how the research team will identify participants approaching the transition, when adult consent will be sought, what activities may occur before that consent is obtained, how missed follow-up contacts will be handled, and what happens if the participant declines continued participation.

This is the sort of protocol detail that is much easier to resolve prospectively than when a research coordinator notices, perhaps with admirable academic timing, that yesterday's minor is today's legally autonomous participant.

The transition can occur at different points for different participants

In a cohort recruited across several ages, participants may reach legal consent age at different study waves. A protocol should therefore track consent status at the individual level rather than treating the entire cohort as though everyone transitions at once.

Multisite studies may be even more complicated if legal rules differ among jurisdictions. Investigators should ensure that site-specific procedures correctly identify when each participant becomes legally capable of consenting to the research activities involved.

A five-year study crosses the boundary into adult consent

The important event is not the birthday celebration itself. It is the change in legal authority to consent to the research procedures. The protocol should be designed around that transition.

Common mistakes when child participants reach legal consent age

Build the transition into every long-term study involving children

If your protocol may follow participants beyond the age at which they can legally consent, treat the transition as a predictable study event. Your consent-management system should be able to identify it before additional research activities occur.

Document these procedures in the protocol, consent plan, data-management workflow, and staff training. A longitudinal study should not depend on individual coordinators remembering participants' birthdays from memory.

Also consider how the transition will be explained to participants before it happens. Adolescents can be told during the original assent process that, if the study continues after they become legally able to consent, researchers may ask them to make their own decision about continued participation.

Before a child participant reaches legal consent age, prepare the transition

Frequently asked questions about reaching legal consent age during research

The participant eventually becomes the person who authorizes continued participation

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