Parainfluenza and croup are often diagnosed by observing the symptoms you are experiencing. A bark-like cough and high-pitched sound when breathing in (inspiratory stridor) are common signs of croup. Your health care provider will also listen to your lungs with a stethoscope. A throat or nasal swab may be taken to determine which virus is causing croup symptoms (most often this is parainfluenza).  

Other tests such as blood work, a chest x-ray, or a CT scan of the chest may be done to rule out other causes, but are often not necessary.