Site Eligibility Funnel: Referral to Randomization

Every research site follows the same basic process. A person shows interest in a study. The site checks whether that person fits the study. If everything lines up, the person is randomized into a study arm. What happens in between is the site eligibility funnel. The shape of that funnel decides whether a study hits its enrollment targets on time.

The scale of that work is large. As of July 2, 2026, ClinicalTrials.gov listed 17,873 recruiting interventional clinical trials with locations in the United States. That number moves daily as trials open, close, and update their status. Behind that number sits a simple reality for every site: many studies are competing for the same pool of people, coordinators have limited hours, and every hour spent on a referral that will not qualify is an hour lost from a referral that might.

This article walks through the funnel one stage at a time. It starts when an external referral arrives at the site and ends at randomization. The goal is to give research teams, sponsors, and referral partners a shared way to talk about where people actually drop out, and why.

Stage 1: External referral arrives at the site

The funnel begins when someone outside the site's own patient panel shows interest in a study. That interest can come from many places. A person may click on a sponsor's ad. A community doctor may send a note about a patient. An advocacy group may forward a family that reached out for help. In each case, the site receives a name, some contact details, and, ideally, enough context to know which study is in play.

At this point the referral is a lead, not a participant. The first job is triage. Is this person a plausible fit for a study the site is actively enrolling? Does the team have the bandwidth to work them up? Sites that treat every referral the same end up spending the same amount of time on high-quality and low-quality leads.

This is where structure at the top of the funnel matters. When referrals arrive already matched to a specific study and already checked against the basic inclusion criteria, the site works from a curated queue instead of a raw feed. That is the role DecenTrialz plays. AI-powered matching narrows the interested population to the studies where they plausibly fit. A registered nurse then pre-screens against the study's early filter criteria before the referral is routed to the site. The site's own research team still handles the full screening visit, the eligibility decision, and the informed consent conversation. What changes is that the referral has already cleared a first pass. The site's time goes to candidates with a real chance of moving forward.

Learn more about how DecenTrialz supports sites at the top of the funnel at decentrialz.com.

For more on the competitive pressure sites face when many studies chase the same referral pipeline, see The recruitment struggle is real: what today's sites need to compete.

Stage 2: Site pre-screening against the study

Once the site accepts a referral into its queue, the next step is pre-screening. This is a structured review, usually done by a coordinator or research nurse. It checks the referral against the study's inclusion and exclusion criteria before any billable study procedure is done.

Pre-screening at the site is deeper than the filter upstream. It usually includes a review of medical records, a phone call with the potential participant, and, when possible, a check inside the health system's electronic health record. The coordinator is looking for hard blockers. Wrong diagnosis. A prior therapy that violates a washout period. A comorbidity on the exclusion list. An age or lab value outside the required range.

A large share of referrals drop out at this stage. Some drops are unavoidable. A person's history simply does not match the study. Other drops trace back to missing information from further up the pipeline. Incomplete records. Missing lab values. Study details that were not communicated clearly to the referring source. When those gaps get closed earlier, more of the referrals that reach the site are viable at pre-screening.

For sites carrying heavy study volume, Pre-screening smarter: how technology reduces screen failures at sites covers the tooling and workflow changes that most directly reduce pre-screen loss.

Stage 3: The screening visit and informed consent

If a referral clears pre-screening, the site schedules a screening visit. This is the first formal visit where the participant meets the research team and study procedures begin.

The order matters and is often misunderstood. Informed consent comes first. Study screening procedures come after. That order is not optional. A person cannot be asked to undergo study-specific labs, imaging, or questionnaires without first understanding what the study involves, what the risks are, and what their rights are as a participant. The investigator, or a qualified team member, walks the participant through the informed consent document, answers questions, and confirms understanding. Only after consent is signed and filed do the formal screening procedures begin.

Drop-out at this stage happens in two main ways. Some participants learn what the study will actually require, such as the time commitment, the visit schedule, or the study intervention (the drug, device, or behavioral component being tested), and decide it is not right for them. Others begin the screening procedures and are found to be ineligible, for example because a lab value falls outside the study's window or an imaging finding matches an exclusion criterion.

Both outcomes are legitimate. The first shows that informed consent is doing its job. The second shows the study's eligibility rules doing their job. Sites should track the split between them. That ratio signals whether the upstream referral pipeline is well matched to the study or whether it is delivering people who never had a realistic chance.

The tone and structure of the screening visit shape participant experience and retention later on; Building a patient-centric culture at your site explores that in more detail.

Stage 4: Eligibility confirmation and randomization

Between the screening visit and randomization sits a short but important stage: eligibility confirmation. This is the point where all screening results are back, the investigator reviews them against the full inclusion and exclusion criteria, and a formal decision is made. In many studies this also includes source verification, which means filing documented evidence for each eligibility criterion in the participant's study record.

Some studies use independent adjudication, such as a central imaging review or a lab core review. In those cases, eligibility can pause here until the outside read comes back. That waiting period is a common source of funnel loss. Participants can withdraw, get sicker, get better, or simply lose interest during the delay. Sites that track their time-in-screening against a documented target tend to catch these stalls early. They either speed up the outstanding steps or declare a screen failure and move on.

Once eligibility is confirmed, randomization follows. The participant is assigned to a study arm using the study's randomization scheme, and the study intervention begins. This is the point the entire funnel is built to reach. It is also the point that reveals, in hindsight, how efficient the pipeline actually was. A site's referral-to-randomization ratio says far more about the health of the funnel than the raw referral count does.

For a deeper operational look at this stage, Reducing screen failures in clinical trials: how sites can improve eligibility matching unpacks the practices that lift the conversion rate between screening visit and randomization.

Diagnosing where the funnel breaks

Every site's funnel has a shape, and that shape tells a story. Two sites with the same referral volume can end up with very different randomization counts, because they lose people at different points.

A funnel that loses heavily at pre-screening usually points to an upstream mismatch. The referral pipeline is delivering people whose basic profile does not fit the study. A funnel that clears pre-screening but loses heavily during screening procedures usually points to study design pressure. The inclusion or exclusion criteria are set at a level that a large share of otherwise reasonable candidates cannot meet. A funnel that loses people between eligibility confirmation and randomization usually points to operational drag. Long screening windows. Slow adjudication. Scheduling friction that gives candidates time to reconsider.

Sites that measure the funnel at each stage, not just referrals in and randomizations out but drop-out counts and reasons at every step in between, can pinpoint the problem and act on it. They can push back on referral sources delivering low-quality leads. They can flag study criteria that are producing outsized screen failures for the sponsor's protocol team. They can restructure their own workflow to shorten time-in-screening. Without that stage-level view, all a site sees is a top-line conversion number that does not tell them what to change.

Screen failure rates vary widely across the industry. Reported patterns range from roughly one in five participants in some indications to more than half in others. The range depends on study stringency, therapeutic area, and how well the referral pipeline is matched to the study. The point is not the specific number. The point is that the number a site inherits from an industry average is not the number that site has to accept for itself.

For the reporting cadences that make funnel visibility legible to the sponsor teams making site-selection decisions on future studies, see Building sponsor trust: metrics that show site performance.

Bringing structure to the top of the funnel

The eligibility funnel is not something a research site can escape. Every study has one. Every protocol shapes it. Every site's operational performance is measured through it. What sites can control is the quality of what enters the funnel and the discipline with which candidates move from stage to stage.

DecenTrialz supports the earliest section of that funnel. AI-powered matching connects interested people to studies where they plausibly fit. Registered-nurse pre-screening applies a first structured filter against the study's early criteria. The referrals that arrive at the site have already cleared that first pass. That means coordinators and investigators spend their time on candidates with a real chance of reaching randomization. The site's research team keeps full authority over screening procedures, eligibility determination, informed consent, and enrollment.

If your site is carrying heavy study volume and looking for a referral partner that reduces the pre-screen loss you absorb from cold leads, visit decentrialz.com to see how the platform structures the top of your funnel.