Impact of a diagnostic strategy for appendicitis in children with acute abdominal pain in primary care: study protocol for a hybrid type 1 cluster randomised controlled trial

BACKGROUND: Children with acute abdominal pain pose a diagnostic challenge for general practitioners (GPs), as it can be difficult to distinguish appendicitis from self-limiting conditions due to overlapping symptoms. To support GPs, a diagnostic strategy for appendicitis was developed that integrates an externally validated prediction rule with C-reactive protein point-of-care testing (CRP POCT) and risk-based management advice. This study will compare the impact of this diagnostic strategy to usual care in children with acute abdominal pain in primary care in terms of: (i) clinical effectiveness, (ii) cost-effectiveness, and (iii) implementation potential. METHODS: We will conduct a pragmatic, hybrid type 1 effectiveness-implementation, cluster randomised controlled trial in Dutch general practice. Children aged 4-18 years with acute (≤ 7 days) abdominal pain will be included. GP practices will be randomly allocated to either: (i) use of the diagnostic strategy for appendicitis, or (ii) usual care. In the intervention group, children are stratified into low, medium, or high risk for appendicitis based on a seven-item prediction rule including symptoms and signs. Management advice is tailored to appendicitis risk: safety netting for low-risk, immediate referral for high-risk, or CRP POCT for medium-risk (CRP < 10 mg/L: safety netting; CRP 10-50 mg/L: reassessment or immediate referral (based on GPs' clinical judgement and parent/child preference); CRP ≥ 50 mg/L: immediate referral). The primary outcome is referral efficiency (proportion of non-referrals amongst patients with no appendicitis during 30 days follow-up). Secondary outcomes include safety, proportion of children with CRP POCT, proportion of children with planned reassessment, child anxiety, patient satisfaction, quality of life, and costs. A parallel process evaluation will assess implementation outcomes, including the reach, adoption, implementation, and maintenance of the diagnostic strategy. We aim to include 566 children without appendicitis to determine an improvement of efficiency from 88% to 95%. DISCUSSION: We hypothesise that use of the diagnostic strategy will reduce referrals without increasing delayed diagnoses of appendicitis, compared to usual care in children presenting with acute abdominal pain in primary care. This may ultimately result in better patient outcomes, lower costs, and reduced health care resource use. TRIAL REGISTRATION: ClinicalTrials.gov: NCT06762275 (registration date: 2024/12/03).