The Eligibility Decision Is Medical

Part of Principal Investigator (PI) Training: Eligibility and the Enrollment Decision.

About 4 minutes. Free, in your language, no account needed.

Why this matters

An ineligible enrollment is the one error you cannot correct. A late form can be filed. A missed visit can be documented. A person who should never have been randomized has already been exposed to a risk they should not have been offered, and their data may be unusable — which means their exposure bought nothing.

Eligibility is where the investigator's medical judgment does the most good, and it is the routine most often reduced to a tick-box exercise run by someone else.

Two questions, not one

The eligibility checklist asks whether each criterion is met. That is necessary and it is not sufficient. The investigator's decision has two parts.

Question one — does this person meet the criteria as written? A factual question, largely answerable from source. A coordinator can assemble the evidence; you confirm it.

Question two — is this trial a reasonable thing for this person? A clinical judgment that no checklist contains. Someone can satisfy every criterion and still be a poor candidate: a participant whose social circumstances make the visit schedule impossible, whose comorbidity makes the risk profile unfavorable in a way the criteria did not anticipate, whose prognosis means the trial's burden outweighs any plausible benefit to them.

Question two is why §2.7.1(a) puts trial-related medical decisions with a physician investigator. Nobody else on the team is positioned to answer it, and no protocol can answer it in advance.

The evidence behind each criterion

Section 2.12.3 is the sub-section to know here: the investigator should be given access to, and is responsible for reviewing, data relevant to the trial — explicitly including data from external sources that affect participant eligibility, treatment or safety, unless access is restricted to protect blinding.

Practically, that means eligibility rests on source you have seen, not on assertions you have been given.

The recurring failure is the criterion assessed from the participant's account alone. "No prior exposure to this drug class" is a reasonable thing to ask a patient and a poor thing to enroll them on. Where the protocol depends on it, get the record.

Recording the decision so it is defensible

Your eligibility decision should be visible in the source record without archaeology. Four elements are enough:

  1. A dated statement that you reviewed eligibility, signed by you.
  2. The specific source relied on for any criterion requiring judgment.
  3. A one-line rationale wherever judgment was applied — a borderline laboratory value, a historical diagnosis of uncertain date, a comorbidity you considered and accepted.
  4. Confirmation that the decision preceded any trial-specific procedure beyond screening.

That fourth point matters. Consent precedes screening procedures; the eligibility decision precedes enrollment and first dose. Getting the sequence right in the record is as important as getting it right in the clinic, because the record is what will be reconstructed.

Borderline values and the temptation to round

Sooner or later a participant will miss a threshold by a trivial margin — a hemoglobin one unit below the floor, a value that would almost certainly be inside the range if repeated. The protocol's rule governs. If it permits a repeat, repeat it and document both results. If it does not, the person is not eligible today.

The uncomfortable truth is that this is not really a scientific judgment in the moment; it is a judgment about whether the criteria mean what they say. Once a site starts treating thresholds as approximate, it has no threshold at all — and the participant carries the consequence.

Key takeaways