acute chest syndrome (MONDO_0005632, a Monarch Disease Ontology identifier) is a vaso-occlusive crisis of the pulmonary vasculature occurring in patients with sickle cell disease. It is characterized by the presence of a new radiodensity on a chest radiograph accompanied by fever, cough, sputum production, dyspnea, or hypoxia. Also known as: ACS, acute chest syndrome in sickle cell disease.