Importance of Spirometry

Spirometry is one of the Pulmonary Function Tests, which is a series of laboratory studies used in diagnosing COPD. It measures the flow and volume of air out of the lungs. An arterial blood gas study determines the level of oxygenation and gas exchange. Pulmonary function tests also measure lung volume and diffusion capacity. Most of these studies must be done in a reference lab, but spirometry can be done anywhere.

In-office spirometry used to be very complicated and difficult to do. Reliable equipment was not available. That is not the case anymore. Today we have spirometers that you can purchase for between $500 and $800 dollars that are as reliable as the $25,000 machine that is in the pulmonary function laboratory.

It should be used as a follow-up in patients with a diagnosis of other airway diseases, like asthma.

Now, the question is who should be tested. Anyone complaining that he or she gets short-winded with even minimal exertion should be tested. It should be used for a patient with a chronic cough, which by definition is a cough that has persisted for more than three weeks. It should be used as a follow-up in patients with a diagnosis of other airway diseases, like asthma. And it should be used for anyone over the age of 40 who smokes, or has smoked in the past. In short, in all of the patients who you suspect have any abnormality in the lungs, because spirometry is going to guide you to the right diagnosis and the appropriate therapy.

Very often when you test a patient who has been referred with a diagnosis of COPD the spirometry result shows that there is no COPD. The patient might have a restrictive lung disease or may have other pathology that has gone undiagnosed and untreated. Spirometry enables an appropriate diagnosis in order to institute appropriate therapy.

In the study conducted in the U.S./Canada and Spain that was cited previously, when the hypothetical patient's spirometry results were added to the equation, the diagnosis for COPD increased to over 70% and was the same for both men and women. There is no way for us to know if a patient has the disease. We underestimate the disease. We have to measure the disease and the only way we can measure the disease is with the use of spirometry.

To summarize, it is important to have spirometry in your office and use it in your practice. It will complement your other diagnostic tools and enable you to diagnose patients with COPD and treat them effectively. It will also help you avoid making a diagnosis of COPD when it is not present.

Spirometry is not difficult to perform. You don't have to worry about calibration because most of the equipment auto-calibrates. You enter the patient's age, sex, height and weight and the result will reflect the average function of the status in the patient. It is simple to do and it is a measurement that can be easily reproduced. This has become the gold standard for the diagnosis of COPD. A spirometry report lists a lot of numbers, a lot of terminology and parameters which can make it confusing, but we focus on three key measurements, the Forced Vital Capacity (FVC), the Forced Expiratory Volume (FEV1) and the ratio of FEV1 to FVC.

Forced Vital Capacity is how much air the patient was able to blow in up to a six-second time. The reality is that if your patient can do up to four seconds, the numbers are going to be appropriate. As the table indicates, after two to three seconds the patient has reached a steady state.

The Forced Expiratory Volume, FEV1, is the volume of air that can be forced out in one second after taking a deep breath. This is a vital value that is going to give you information related to the patency of the airway and how much obstruction exists in the airway — how easy it is for the air to flow out of the lungs.

The ratio of FEV1 to FVC is what GOLD and other organizations have established as determining the severity of the patient's obstruction. If a patient's ratio is less than 70% there is an obstruction. A ratio of 30% has severe COPD. A patient with a ratio of more than 80% has mild COPD. These percentages are important in determining harmacotherapy and what kind of interventions the patient should receive.

Several organizations and groups believe that we should include the FEV1 result as one of the vital signs. When a patient comes into your office, you have to know that blood pressure, pulse and respiratory rate are okay. It is also very important to know the patient's smoking status. If the patient is an active smoker, you will have to intervene. If he or she is a former smoker, this is a red flag. Even if the patient has stopped smoking she or he may have COPD.

The National Lung Health Education Program (NLHEP) is an organization that reviews the different spirometers that are available. Their website (see Resources) compares equipment. It will give you a rating of the adequacy of the spirometer and a rating of the value relative to price. There are a number of billing codes you can use for a spirometry and you can also bill for interpretation of the spirometry. Early recognition of the reduction of lung function can lead to specific treatment plans that may potentially slow the progression of the disease.