Spirometry is a technique used to measures the amount of air moving in and out of the lungs during various respiratory maneuvers. It allows one to determine how much air can be inhaled and exhaled, and how fast. The test involves having a patient blow forcefully into a mouthpiece connected to the spirometer for up to six seconds. It is usually easily performed by children older than seven years of age but can be done in some children as young as 4 years of age. By measuring how much air is exhaled, and how quickly, a spirometry can evaluate a broad range of lung diseases and can help assess the progression of lung disease and monitor the effectiveness of therapy. To get the “best” test result, the test is repeated three times and American Thoracic Society (ATS) Guidelines are used to determine if the test has been effectively and acceptably performed.