Diagnosing Asthma

Diagnosing asthma can be tricky simply because most asthmatics only have occasional symptoms. For most people, asthma tends to come and go with symptom-free periods that can last for days or months. If you see your doctor when you're not having symptoms, it may be difficult to establish the diagnosis. Adding to this difficulty is that, even among physicians, there is controversy over how to define asthma. Despite this, most physicians will use personal history followed by a variety of clinical and laboratory tests to make the diagnosis.

 

Most doctors can make a presumptive diagnosis of asthma after listening to your complaints and doing a physical exam. To establish a diagnosis, however, formal pulmonary testing is needed. The "gold standard" for measuring lung function is called the Pulmonary Function Test (PFT). During the PFT, a person blows into a machine that measures a variety of lung volumes. Sometimes a less complicated machine called a spirometer is used to make these measurements. For the asthmatic, the most important measurements are the Forced Expiratory Volume (FEV) and Forced Expiratory Volume in One Second (FEVi).

 

FEV is the volume of air you can force out from your lungs. FEV is measured by having you take the deepest breath possible, then blowing all the air out into the PFT machine. FEVi is the amount of air you can blow out in one second after taking the deepest breath possible. By measuring FEV and FEV1, we can determine how well your lungs work. If FEV and FEV1 are measured during as asthma attack, the severity of the attack can be accurately determined.

 

Normal FEV and FEV1 values vary from person to person and depend in part on age and height. As we age, there is a normal reduction in lung function that is reflected by a lower FEV and FEV1. Conversely, the taller you are, the bigger your lungs tend to be, which can increase your FEV and FEV1. FEV and FEV1 measurements are expressed as a percentage of predicted normal. Given the wide fluctuations in asthma, FEV and FEV1 can range from perfectly normal to less than 10 percent of predicted normal. In fact, most asthmatics have normal FEV and FEV1 except when they have an attack.

 

Asthma symptoms are usually perceived when FEV drops below 50 percent of predicted normal or the RV doubles. RV, or residual volume, is another lung measure representing the amount of air left in the lungs after completely exhaling. As mentioned earlier, asthma has more to do with not getting air out of the lungs than getting air in, and during an attack air can be trapped in the lungs. During a severe attack, RV can increase to four times normal.

 

While FEV and FEV1 are useful measures of lung function, these measurements alone cannot definitively establish a diagnosis of asthma. First of all, the measurements must be taken during an attack. Second, even if FEV and FEV1 are abnormal, this finding can be caused by another medical condition, such as emphysema or chronic bronchitis. In order to nail a diagnosis of asthma, we have to demonstrate hyperreactivity and reversibility, in addition to recording abnormal FEV and FEV1.

 

Asthmatic airways are overly sensitive, or hyperreactive, which can lead to reversible bronchoconstriction. We test for hyperreactivity by measuring the reduction in FEV and FEV1 after inhalation of a known bronchoconstrictor, such as methacholine, histamine, or cold air. Most people will experience mild airway narrowing when exposed to these stimuli; however, asthmatics have an exaggerated response that results in significantly abnormal FEV and FEV1.

 

Once we have established that the lungs are hyperreactive, we can then test for reversibility by giving the patient a bronchodilator and remea-suring FEVj. An increase in FEV1 of 15 percent or more after bronchodilator inhalation is considered a positive test for reversible bronchoconstriction. Hence, a definitive diagnosis of asthma can only be made with an appropriate clinical history coupled with PFT-documented airway hyperreactivity and reversible bronchoconstriction.

 

Many doctors feel comfortable diagnosing asthma on clinical grounds alone, with PFT reserved for those cases where the diagnosis is in question. I believe that most people with wheezing should have a PFT as well as a bronchoconstrictor challenge. These tests are recommended not only to measure asthma severity but also to establish a definitive diagnosis, excluding the possibility of misdiagnosis.

 

Should you be concerned about receiving the wrong diagnosis? Presented with the classic symptoms, most doctors are correct when they make a diagnosis of asthma. Nobody is perfect, however, and when a doctor makes a mistake in diagnosing asthma, the consequences can be severe. This is why it is always wise to get a second opinion. You may learn that your asthma is not as severe as first suspected or discover that you don't even have asthma.

 

Warning signs that may mean misdiagnosis include a new diagnosis of asthma over age forty or symptoms that fail to get better with treatment. Most people with asthma are diagnosed prior to age forty and any new diagnosis after age forty should be held suspect. Suspicion is also warranted for the patient who does not respond to standard therapy. For a physician, this means one of five things:

 

 

A healthy dose of skepticism never hurt and will keep your doctor on his or her toes. Remember, it's your life, not the doctor's, and you have the most to lose in all of this. You and your doctor should also be aware that there are several medical conditions that can masquerade as asthma and may need to be eliminated as possibilities.

 

Because GERD is such a common condition and a known asthma trigger, talk to your doctor about being tested for GERD, especially if you have symptoms like heartburn. Many asthmatics report improved symptoms once their GERD is treated.

 

Dysfunctional breathing goes by many names, including behavioral breathlessness and hyperventilation syndrome. No matter what you call it, dysfunctional breathing adds up to a breathing disorder characterized by hyperventilation. Not only does dysfunctional breathing contribute to asthma, but it can be mistaken for asthma and lead to a misdiagnosis. It is suspected that therapies like Buteyko Breathing and yoga are so helpful to asthmatics because they train people how to breathe properly. Given how common dysfunctional breathing is among asthmatics, ask your doctor if this disorder may be contributing to your symptoms.

 

Asthmalike symptoms can also be caused by chronic bronchitis. Bronchitis is an inflammation of the large airways and is usually caused by infection. Like GERD, treating the bronchitis may cure the "asthma." Another lung disorder that can cause asthmalike symptoms is allergic bronchopulmonary aspergillosis, a fungal infection of the lung. People with heart failure can have their symptoms confused with asthma, because heart failure can cause pulmonary edema that results in wheezing and shortness of breath. Known as "cardiac asthma," these symptoms disappear once the heart problem is treated.

 

Bronchiectasis is an uncommon medical condition in which the lung's airways become dilated and stiff, resulting in asthmalike symptoms. The glottis, which helps keep food you swallow from entering your lungs, can also cause airway obstruction if it is not working properly. Other rare conditions that can cause airway problems are tumors, foreign bodies (for example, accidentally swallowed objects), vocal cord dysfunction, and laryngeal (voice box) edema.

 

When visiting your doctor, suggest the possibility that another medical condition is causing your symptoms. Chances are, if your doctor thinks you have asthma, you probably have asthma; however, by mentioning these possibilities, you get your doctor to think more broadly about your condition and, if indicated, order the necessary tests.