To better understand the use of the fixed ratio from spirometry to support a diagnosis of airflow obstruction, it is important to clarify some definitions. A diagnosis is a label given for a medical condition or disease identified by its signs, symptoms, and from the results of various diagnostic procedures (tests). COPD therefore is a disease, and its diagnosis is supported by a test. Spirometry is a test from which values are derived to help determine the function of the respiratory system. Thus, we cannot confuse the results of a test (spirometry) as a diagnosis proper with its use as a tool to support a diagnosis.