D23-14 CT-Sparing ILD Monitoring: An Evidence-Derived Algorithm Integrating Lung Ultrasound, Digital Auscultation, and FVC Trajectories

Rationale Repeated high resolution computed tomography (HRCT) is the monitoring anchor in fibrotic ILD but imposes radiation, cost, and access burdens. We asked whether validated non-ionizing signals—lung ultrasound (LUS) B-lines/pleural changes, digitally detected “Velcro” crackles, and forced vital capacity (FVC) trajectories—support a pragmatic algorithm to reduce discretionary HRCT without sacrificing safety. Prior studies report strong LUS-HRCT concordance and high diagnostic accuracy of digital crackle detection; FVC decline remains a robust progression marker. Methods We registered a protocol and conducted a PRISMA-conform systematic review (MEDLINE/Embase/Cochrane/CINAHL, inception-September 2025). Inclusion: adults with ILD or CTD-ILD; index tests LUS and/or digital auscultation and/or longitudinal FVC; reference HRCT or adjudicated progression. Outcomes: diagnostic accuracy, agreement, and longitudinal associations. Two reviewers screened/extracted; risk of bias (QUADAS-2/QUIPS). Using prespecified accuracy thresholds from individual studies, we synthesized an evidence-derived “CT-Minimal” clinic algorithm and performed a rule-in/rule-out decision analysis anchored to reported cut-points (no new patient recruitment). Results Twenty-three studies met criteria. Key reproducible anchors were: (1) LUS B-lines ≥10 identified significant ILD versus HRCT with sensitivity 96.3% and specificity 92.3% in systemic sclerosis (Warrick≥7), with strong LUS-HRCT correlation (ρ≈0.82-0.96). Examination time ≈9 minutes. (2) Digital auscultation (VECTOR) detected CTD-ILD with accuracy 82.6% (sensitivity 88.1%, specificity 78.6%) against HRCT. (3) Physician agreement for digitally recorded crackles in fibrotic ILD was moderate-to-good (κ 0.57 overall; intra-rater up to 0.87), supporting longitudinal use. (4) FVC decline is firmly linked to progression/mortality; contemporary cohorts and registries validate FVC change as the principal clinical end point. New contribution: We operationalized a CT-Minimal algorithm: defer HRCT when all are true—LUS <10 B-lines without pleural irregularity; negative digital crackle screen; no absolute FVC decline ≥5% over 6-12 months—while obtaining HRCT when any criterion is positive. Mapping these thresholds onto the accuracy estimates above indicates high rule-out safety for significant ILD and provides a structured pathway to reserve HRCT for progression signals. Conclusion High-quality studies show that LUS, digital auscultation, and FVC trajectories carry actionable signals in fibrotic ILD. An evidence-derived algorithm can rationalize HRCT use and is ready for prospective validation as a clinic workflow to cut radiation exposure while maintaining vigilance for progression.