Agile evaluation including two pragmatic trials on the uptake of a digital screening service

Digital screening may divert lower-risk persons to lower-cost online screening, or offer higher-risk non-responders a more acceptable alternative. Population-based uptake estimates are lacking. We conducted four studies within four weeks by inviting 1700 Londoners (40-74 years, without cardiovascular disease) to a digital Health Check. A six-arm pragmatic unregistered randomised controlled trial (RCT) tested different Short Message Service (SMS) invitations. Uptake varied from 12% (standard SMS) to 20% (shortest SMS, P = 0.009). We tested three sequential reminders (an SMS, a second pragmatic trial [SMS vs postal reminder], and a final SMS). The first SMS reminder increased uptake by +3%. The postal reminder (+7%) was twice as effective as the SMS reminder (+3%, P < 0.0001). The "final reminder" SMS added +7%. Altogether, shorter invites, multi-modal reminders, and a "final reminder" all increased uptake. Adding digital care to in person care may raise uptake from 50 to 60%. Agile evaluations can rapidly improve invitation systems.