Concerns about inadequate performance and complexity limit routine use of clinical risk scores in lower respiratory tract infections. Our aim was to study feasibility and effects of adding the biomarker proadrenomedullin (proADM) to the confusion, urea>7 mmol·L(-1), respiratory rate≥30 breaths·min(-1), blood pressure<90 mmHg (systolic) or ≤60 mmHg (diastolic), age≥65 years (CURB-65) score on triage decisions and length of stay. In a randomised controlled proof-of-concept intervention trial, triage and discharge decisions were made for adults with lower respiratory tract infection according to interprofessional assessment using medical and nursing risk scores either without (control group) or with (proADM group) knowledge of proADM values, measured on admission, and on days 3 and 6. An adjusted generalised linear model was calculated to investigate the effect of our intervention. On initial presentation the algorithms were overruled in 123 (39.3%) of the cases. Mean length of stay tended to be shorter in the proADM (n=154, 6.3 days) compared with the control group (n=159, 6.8 days; adjusted regression coefficient -0.19, 95% CI -0.41-0.04; p=0.1). This trend was robust in subgroup analyses and for overall length of stay within 90 days (7.2 versus 7.9 days; adjusted regression coefficient -0.18, 95% CI -0.40-0.05; p=0.13). There were no differences in adverse outcomes or readmission. Logistic obstacles and overruling are major challenges to implement biomarker-enhanced algorithms in clinical settings and need to be addressed to shorten length of stay.