How to recruit patients for a clinical trial: a small-trial playbook

The most common recruitment plan is a target number copied from the sample size and a hope that sites will find the patients. A better plan starts from the other end. For each site, ask how many patients with the condition they saw in the last twelve months, how many of those would pass your inclusion and exclusion criteria, and how many would plausibly agree to the visits you are asking for. The gap between the first and last number is typically large, and it is better to learn that from a chart review than from a stalled study.

Read your own eligibility criteria as a recruiter would. Each criterion removes people. A washout period, a narrow age band, a required lab value or a restriction on concomitant medication can each cut the pool by a large share. If a criterion is there for scientific reasons, keep it. If it is there out of habit, the protocol is the cheapest place to fix recruitment, before approval rather than through an amendment. Our guide to how to write a clinical trial protocol covers this trade-off.

For a small trial, also ask whether the visit burden is realistic. Weekly clinic visits for a working adult shrink the pool. Hybrid designs, remote questionnaires and fewer, longer visits can widen it. See edc for hybrid clinical trials and how to run a pilot study if you are testing whether the design is workable at all.

A short pre-screening questionnaire saves everyone time. It checks the criteria a participant can reliably self-report, such as age, diagnosis, medication and availability, before a site schedules a visit. It does not replace the formal eligibility assessment, and it should collect no more personal data than it needs. See online patient screening for clinical trials and clinical trial pre-screening tools for the design of these flows.

The screening and enrolment log is the record that makes your funnel measurable. For every person assessed, it notes the date, the outcome (consented and enrolled, consented but screen failed, declined, not eligible) and the reason. Reasons matter more than counts. If a third of screen failures trace to one lab threshold, you have found your recruitment problem and a potential protocol question. The screening and enrolment log template is a ready starting point, and an eligibility screening eCRF captures the same decisions inside the study record.

In Capture, participants can join through a QR code, either site-specific or study-specific, with no app install. Participant numbers are assigned per site (for example 001-0042), the site coordinator portal gives staff their own view, and data and exports can be filtered by site. That makes it practical to see recruitment by site on one screen rather than collating spreadsheets from each coordinator.

Consent is where interest becomes commitment, and it is also where people quietly leave if the document is long and unreadable. A consent form written in plain language, with the visit commitments up front, converts better and produces fewer withdrawals later. The informed consent readability checker helps you test the draft. With eConsent, participants sign on-screen after confirming by email one-time code, the investigator countersigns with re-authentication, and the signed document exports as a PDF with the signature data and audit trail.

Retention deserves its own plan. List the reasons a participant in your design would leave: travel, time off work, unpleasant procedures, unclear next steps, diary fatigue. Then design against each one. Fewer, better-timed visits, reminders for questionnaires, and a named person participants can contact all help. ePRO diaries that participants complete on their own phone reduce clinic visits, and the ePRO compliance reminders page covers prompting without nagging. Reimbursing expenses promptly, within what your ethics committee has approved, also protects retention.

Finally, plan for the participants who withdraw. Record the reason, keep the data collected up to withdrawal as your protocol and consent allow, and use what you learn. A cluster of withdrawals at the same visit tells you that visit is the problem.

Look at the funnel before you change anything. If pre-screening volume is low, the problem is reach, and the fix is a new or better channel. If volume is fine but few are eligible, the problem is the criteria or the message. If eligible people decline, look at the burden and the consent. Treating all three as one problem, and buying more advertising, is the expensive way to learn this.

Where a change to the protocol is justified, do it properly: ethics approval, updated registration where relevant, and an updated data system. With a self-serve system you can amend an approved form yourself in a draft-then-approve cycle, which keeps amendments from becoming vendor negotiations; see protocol amendments without change orders. Add sites rather than stretching existing ones if the pool is the limit, and use multi-site clinical trial management and patient recruitment software to keep new sites on the same records.

Capture is a data platform, not a recruitment marketplace: it does not find patients for you. What it does is make each step of the funnel visible in the same record as the clinical data, so decisions rest on numbers rather than coordinator impressions.