Spirometry is indispensable in establishing airway obstruction, and how this condition responds to treatment. It is therefore an important tool in the diagnosis and treatment of respiratory disease. The clinical picture, however, is always of paramount importance.
An example. The diagnosis ‘asthma’ need not be rejected if the patient does not have demonstrable airway obstruction at the time of measurement; if the history is unambiguous spirometric data within the normal range indicate that the condition is not clinically alarming. Indeed, in spite of a ‘normal lung function’ you might, in particular in the case of a first contact with a patient with a history of asthma do consider testing the effect of a bronchodilator drug. Bronchodilator responsiveness would strengthen the diagnosis, whilst lack thereof would still not exclude asthmatic attacks at another time. Similarly, in a patient with COPD symptomatic improvement not accompanied by an improved FEV1 means that the patient rather than the physician records a beneficial effect.
The physician has access to a multitude of data: history, previous medical record, family and professional history, physical examination, clinical impression, spirometric data, etc. Ultimately the physician makes a clinical diagnosis by weighting each piece of information, and then decides on a line of action. The clinical picture is decisive, consequently professionally obtained spirometric data are indispensable in decision making.