Point-of-care lung ultrasound is now widely used to evaluate acutely breathless patients, but the way it integrates with laboratory markers in different age groups and emergency settings is less clearly described. This systematic review summarizes clinical studies that used lung ultrasound to diagnose acute pulmonary conditions in adult and pediatric emergency or critical-care settings, with particular attention to protocols that combined imaging with biomarkers such as procalcitonin and natriuretic peptides. Electronic databases were searched up to 30 November 2025 for prospective or observational studies evaluating lung ultrasound in acute respiratory or hemodynamic emergencies. Studies in adult or pediatric patients with suspected pneumonia, cardiogenic pulmonary edema, ventilator-associated pneumonia or undifferentiated acute dyspnea were eligible if they reported diagnostic accuracy or management outcomes and used a clearly defined reference standard. Nine clinical studies met the criteria. Lung ultrasound consistently showed higher or comparable sensitivity to chest radiography for pneumonia and provided rapid bedside differentiation between cardiac and non-cardiac causes of dyspnea. Algorithms that combined lung ultrasound with procalcitonin or natriuretic peptides improved specificity for bacterial infection or heart failure and reduced unnecessary imaging or antibiotic exposure in pediatric intensive care. Evidence is still limited by heterogeneity and small samples for some laboratory-integrated protocols, but the overall signal supports lung ultrasound as a central tool for emergency pulmonary assessment in age groups.