Bronchiolitis may be diagnosed on the basis of clinical signs and symptoms. In a young child, the diagnosis can be made on the clinical
pattern of wheezing and hyperinflation.
Clinical symptoms and signs typically start with an upper respiratory prodrome, including rhinorrhoea, low-grade fever, cough and poor
feeding, followed 1 - 2 days later by tachypnoea, hyperinflation and wheeze as a consequence of airway inflammation and air trapping.
The illness is generally self limiting, but may become more severe and include signs such as grunting, nasal flaring, subcostal chest wall
retractions and hypoxaemia. The most reliable clinical feature of bronchiolitis is hyperinflation of the chest, evident by loss of cardiac
dullness on percussion, an upper border of the liver pushed down to below the 6th intercostal space, and the presence of a Hoover sign
(subcostal recession, which occurs when a flattened diaphragm pulls laterally against the lower chest wall).
Measurement of peripheral arterial oxygen saturation is useful to indicate the need for supplemental oxygen. A saturation of <92% at
sea level and 90% inland indicates that the child has to be admitted to hospital for supplemental oxygen. Chest radiographs are generally
unhelpful and not required in children with a clear clinical diagnosis of bronchiolitis.
Blood tests are not needed routinely. Complete blood count tests have not been shown to be useful in diagnosing bronchiolitis or guiding
its therapy. Routine measurement of C-reactive protein does not aid in management and nasopharyngeal aspirates are not usually done.
Viral testing adds little to routine management.
Risk factors in patients with severe bronchiolitis that require hospitalisation and may even cause death, include prematurity, congenital
heart disease and congenital lung malformations.