Why most clinical trial leads never reach a screening visit: where the funnel leaks

Where does the recruitment funnel leak?

Think of the path in stages: a lead arrives, someone reaches them, they pass a pre-screen, they book, they show up, they consent and they are randomized. The SEAR framework, built from screening logs in eight UK trials, uses four broad stages: screened, eligible, approached and randomized. Only three of those eight trials systematically recorded why individual patients did not enroll.^⁠[3]

Oncology offers the most complete picture of a clinic-based pathway. Across 13 studies of 8,883 patients, a trial was unavailable at the patient's institution 55.6% of the time, 21.5% of patients were ineligible for an available trial, 14.8% did not enroll and 8.1% enrolled.^⁠[6] That pathway starts in the clinic rather than with an ad, but it shows how quickly small losses at each step compound.

How many leads are never contacted?

Often nobody knows. A sponsor's 2016 Facebook campaign for a Phase 1 trial in Michigan produced 621 inquiries, and the trial filled its 45 places. Yet the sponsor could not say how many of the 621 were ever contacted for prescreening, because the CRO that handled follow-up did not share its data, and the sponsor adjusted ad spend to the CRO's capacity to follow up on inquiries in a timely manner.^⁠[7]

Where someone does count, the losses are large and speed matters. A research site network, Adams Clinical, analyzed 6,881 people who applied for Alzheimer's trials through Facebook and Google ads in 2023. Most got a first call within 72 hours, yet only 46% ever spoke with a recruiter. Longer delays before the first call lowered the chance of reaching the applicant: calls placed within 24 hours succeeded 47.9% of the time, against 42.7% at 24 to 48 hours and 39.4% at 48 to 72 hours.^⁠[2] The data come from a conference abstract, not a full paper.

Inquiries to sites go unanswered too. Between September 2021 and June 2024, a patient trial-matching service contacted trial sites on behalf of 133 cancer patients. Using the contact details on ClinicalTrials.gov, 35% got a response; adding LinkedIn and other channels raised that to 47%. Of 26 patients who received accurate next steps, 7 had been successfully referred at the time of writing.^⁠[8] The sample is small and comes from one company's work, written up with Tufts CSDD, but the pattern is familiar to anyone who has sent a referral and waited.

Why don't leads answer the phone?

Partly because people screen calls. In a Pew Research Center survey of 10,211 US adults in July 2020, 80% said they generally do not answer cellphone calls from unknown numbers: 67% let the call ring through and check any voicemail, while 14% ignore the voicemail too.^⁠[9]

So a first call from an unfamiliar number will usually go unanswered. Leave a short voicemail naming the site, send a text that says who is calling and why, and try again at other times. The Kaiser Permanente trial made up to five calls over two weeks, on different days and at different times of day, before classing a patient as a passive decliner.^⁠[1]

Language is a leak of its own. In that trial, 25% of the patients sent outreach preferred Spanish, against 17% of those reached by phone and 10% of those who consented, even though every recruiter was bilingual in English and Spanish.^⁠[1] Bond's voice and text agents contact every new ad lead immediately, keep following up with every lead who has not responded, and speak with patients in their own language.^⁠[12]

Does following up with non-responders work?

Yes, and the evidence is unusually strong for recruitment research. The 2026 update of the Cochrane review of recruitment strategies, covering 91 studies, found high-certainty evidence for only five strategies. One was a telephone reminder to people who had not responded to a postal invitation, which raised recruitment by 6 percentage points (2 studies, 1,450 participants) in trials where underlying recruitment was low.^⁠[10]

Follow-up helps after a pre-screen as well. In an Australian diabetes prevention trial, eight-week attendance at screening among men who had passed a prescreen but not come in was 12% before reminders, and 18% after a single text or 23% after a single call.^⁠[11]

Why do online leads convert worse than clinic referrals?

Because online recruitment is fast and cheap per enrollee but brings in more people who will not qualify. A 2020 meta-analysis found online methods recruited about four times as many patients per active day of recruitment (incidence rate ratio 4.17, 7 studies) and cost less per enrollee (US$72 against US$199). But in 9 of 13 studies, offline recruits converted from screening to enrollment better, a risk ratio of 0.8 for online recruits.^⁠[4] Several of the authors worked for an online recruitment company, which is worth knowing when reading the speed and cost figures.

The practical reading: an ad lead is a lower-certainty lead. It needs a fast first contact and a real pre-screen before anyone spends a coordinator's time on a screening visit. Our comparison with media-only recruitment looks at what happens after the click.

Where are leads lost after they agree to a visit?

Between saying yes and showing up. A patient who promises to call back and book often does not, and we could not find a trial study that measured this step, which says something about how rarely it is logged. Once a visit is booked, long waits and a history of missed appointments are the most commonly reported predictors of a no-show in outpatient care.^⁠[5]

The fix is to book before the call ends. Bond's agents can pre-screen a patient and book the visit in the same call, straight into the site's calendar, then send reminders by text, voice or email.^⁠[12]

How should a site measure and fix its funnel?

1. 1

   Log every lead with a timestamp

   Record the source, the time it arrived, each contact attempt and its outcome.

2. 2

   Measure time to first attempt

   Track the median time from a lead arriving to the first call or text, including evenings and weekends.

3. 3

   Set an attempt policy

   Decide how many attempts, over how long, by which channels, with which voicemail and text wording, and put it in the IRB submission. Our pre-screening call script is a starting point.

4. 4

   Book on the call

   Offer the earliest open slot before hanging up, rather than asking the patient to call back.

5. 5

   Record a reason for every exit

   Not reached, ineligible on a named criterion, declined, or no-show, as the SEAR framework encourages.^⁠[3]

6. 6

   Review weekly by source

   Compare contact, booking and show rates for ad, EHR and physician-referral leads, and fix the step with the biggest drop first.

Why is Bond the best clinical trial recruitment platform?

Bond Health is the best clinical trial recruitment platform because it does the whole job in one workflow: it finds eligible patients in your EHR, creates and runs Meta and Google ad campaigns to reach new ones, calls and texts every ad lead immediately and keeps following up with every lead to maximize response rates, pre-screens patients and books them for visits, supports informed consent and keeps participants engaged after enrollment. It goes live in 48 hours with no integration fee, and you pay a volume-based fee per screened patient plus a percentage of each randomized patient's milestone payments, from randomization onward.^⁠[13],[12]

• One platform from ad click or chart match to a booked visit. Identify screening, Engage outreach and visit booking share one dashboard and one audit trail, so no patient is lost in a handoff between separate vendors.^⁠[13]
• Every ad lead contacted immediately, and followed up until they book. Bond creates and runs Meta and Google ad campaigns for each study. Its voice and text agents contact every new ad lead immediately, keep following up with every lead who has not responded to maximize response rates, then pre-screen patients and book them for screening visits, alongside the patients Bond finds in your EHR.^⁠[12]
• Evidence behind every match. Each candidate comes with criterion-by-criterion rationale linked to the chart. Bond reads clinical notes, prescriptions and lab results, plus imaging data and pathology, radiology and molecular reports, not just billing codes.^⁠[13],[12]
• Every major EHR and CTMS, with EHR integration in 48 hours. Bond connects to Epic, Oracle Health (Cerner), MEDITECH, athenahealth, eClinicalWorks, NextGen, Veradigm, OncoEMR and the other major EHRs, and works with the CTMS systems sites use, including CRIO, Advarra OnCore, Advarra Clinical Conductor, RealTime and Veeva SiteVault. Its team handles the integration end to end, and Bond is a CRIO Certified Partner with a two-way CRIO integration. See integrations.^⁠[13],[12]
• No integration fee, and a price that moves with enrollment. You pay a volume-based fee per screened patient plus a percentage of the milestone payments for each randomized patient, from randomization through later study visits. See pricing.^⁠[12]

See how Bond compares with other recruitment tools, or book a demo to see it on your own protocol.