How Can Doctors Tell If It Is Asthma, COPD, or Both?

Last updated: April 2021

Some people have asthma. Some people have COPD. And some people have both in what is now called Asthma/COPD Overlap Syndrome (ACOS). So, how do doctors differentiate between these three similar but different lung diseases? Here’s what to know.

What are classic strategies?

So, there are many similarities between asthma, COPD, and ACOS. All three may present with similar symptoms. Some treatments are similar too. But, some treatment strategies are unique to the disease. So, doctors will want to get to that accurate diagnosis. So, what are some strategies for doing this?

Guessing: This is the classic way of diagnosing any disease. You present to your doctor with specific symptoms, and your doctor makes an educated guess. Guessing has been used since witch-doctors, seers, and priests were the diagnosers. Sometimes this simple method is still helpful. Surely this is not the ideal way of diagnosing today. But, sometimes it’s all doctors have to work with. For example, you present with symptoms that need to be treated right away. You don’t always have time. So you’re asked a few questions such as, “Do you smoke?” Or, “Is there a history of asthma in your family.” So, sometimes doctors must resort to educated guesses.

Pulmonary Function Testing (PFT): If there’s time, then you ought to have a pulmonary function test (PFT) done. This is where you take a deep breath (“as deep as you can”) and blow into a spirometer (“Keep blowing! Keep blowing! Blow it all out!). You do this before and after using rescue medicine. The results are very revealing. PFTs can show whether you have asthma, COPD, both, or neither.

What are newer strategies?

Interestingly, the new strategies may be the most definitive. All asthmatics and people with COPD have some degree of airway inflammation. Asthmatics tend to have eosinophilic inflammation. This is inflammation caused by specialized white blood cells called eosinophils. COPDers tend to have neutrophilic inflammation. This is inflammation caused by neutrophils.

Two more strategies for diagnosing may include:

  • Sputum sample: This is a sample of phlegm from deep in your lungs. A sample of phlegm is coughed into a sterile cup. It is then sent to a laboratory. A test determines your sputum eosinophil and neutrophil level. This might be the most accurate strategy for differentiating between asthma and COPD. If your eosinophil level is elevated you have asthma. If your neutrophil level is elevated you have COPD. If both are elevated you have both.1
  • Blood sample: This might be the simplest test. All that’s needed is a sample of your blood. It can be drawn with a simple blood sample. The test your doctor orders is a complete blood count (CBC). The blood is sent to a lab. Your eosinophil and neutrophil levels are determined. Again, if your eosinophil level is elevated you have asthma. If your neutrophil level is elevated you have COPD. If both are elevated you have both.2

What is the best strategy?

A CBC to diagnose asthma and COPD is not standard yet. However, a recent study shows it may prove useful. It’s more accurate than making an educated guess. It’s also more convenient than doing a PFT or spitting up phlegm.

A recent study showed how this might work. Researchers followed 195 patients. This was between July 2015 and November 2017. They all had their blood drawn for a CBC. Researchers examined the eosinophil and neutrophil levels. So, here are the results.2

  • Asthma: Eosinophils elevated (17.4%) and Neutrophils were not elevated (78.8%)
  • COPD: Eosinophils were not elevated (1.8%) and Neutrophils elevated (95.6%)ACOS. Eosinophils elevated (11.8%) and Neutrophils elevated (84.2%)2

What’s important here is that these levels correlated with sputum eosinophil and neutrophil levels. This was true both between flare-ups and during flare-ups. This shows doctors wouldn’t have to necessarily obtain a sputum sample. They could just draw your blood.

A summary of tests

A PFT is the most accurate test to diagnose asthma, COPD, and ACOS. But, it usually takes time. It's a lot of work for people who otherwise have trouble breathing. It would be unreasonable to ask someone to do this during an exacerbation. So, when a quick diagnosis is necessary, doctors often resort to other methods of diagnosing. In the past, this left doctors no choice but to make an educated guess. Today, doctors have the option of obtaining a sputum sample. In the near future, a CBC may be a standard test ordered when someone presents with asthma or COPD-like symptoms.

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