Blood analysis may show increase in the number of eosinophils (Eosinophil is a specific type of white blood cell that increases in allergic reactions).

 Sputum examination may show increased eosinophils 

 The level of a certain antibodies can be elevated.

 Chest X ray may show abnormality in the airway.

Arterial blood gas analysis shows decreased oxygen concentration in blood.
Pulmonary function tests (lung function tests) are helpful in judging severity of airway obstruction. To do this test a spirometer is used and the test is often called spirometery. A spirometer is an instrument that measures the maximum volume one can exhale after breathing in as much as one can. There are various values that are calculated and the interpretation of the test is done looking at a combination of values. Some of the common values looked at are as follows:

Forced Vital Capacity: or FVC: This is the total volume of air one can exhale after breathing in as much as one can inhale

Forced Expiratory Volume in One Second, or FEV1: This measures the volume of air one can exhale in the first second. In general, the more air you breath out during the first second of a full exhalation, the better.