“Eosinophilic asthma is a newer concept underneath the umbrella of severe asthma,” says Geoffrey Lowell Chupp, MD, director of the Yale Center for Asthma and Airways Disease in New Haven, Connecticut. According to the National Heart, Lung, and Blood Institute, about half of people with severe asthma have high levels of eosinophils in their lungs and blood, which can cause inflammation and swelling in the airways and other parts of the respiratory system. Eosinophils often don’t respond to typical asthma treatments, such as inhaled corticosteroids. But new drugs have been developed to target eosinophils, and people with asthma who have high levels of eosinophils can benefit from these treatments, says Dr. Chupp. So if you’re struggling to control your asthma symptoms despite following your treatment plan, talk to your doctor about getting tested for eosinophilic asthma, or e-asthma. Chupp recommends seeing a specialist who understands the intricacies of managing patients with severe asthma. In addition to the basics, like taking your medical history, performing a physical exam, and reviewing your current asthma treatments, your doctor will perform one or more tests to measure your eosinophil levels. Sometimes it takes some sleuthing to find out why your asthma symptoms are still uncontrolled. “Physicians taking care of patients with asthma have to use their clinical acumen and the tests to determine what the patient has,” says Chupp.
Tests Used to Diagnose Eosinophilic Asthma
There are three main tests used to measure your level of eosinophils. Here’s what you need to know about each.
Blood eosinophil count
A blood test is commonly used to measure levels of eosinophils in your blood. It’s a simple blood draw, similar to a cholesterol or blood sugar screening. Though, you don’t need to fast before this blood test. How it works: The sample is sent to a lab for a complete blood count with a differential of your white blood cells to reveal your eosinophil levels, says Chupp. A normal blood test reading typically shows fewer than 500 eosinophils per microliter (mcL) of blood; a reading over 500 indicates blood eosinophilia (elevated levels of eosinophils). However, lower counts can still indicate a problem. For example, if a person has severe asthma symptoms despite treatment with inhaled steroids and prednisone, eosinophil counts above a few hundred cells/mcL can be a marker of eosinophilic asthma, says Chupp. In other words, there’s no magic number. “It’s just a marker to help us understand if a patient is going to respond to specific treatment targeted against eosinophils,” says Chupp. Important to know: While this test is a good indicator of the level of eosinophils in your blood, it doesn’t necessarily confirm that you have eosinophils in your lungs.
Sputum eosinophil count
This test measures eosinophils in your sputum, a mixture of saliva and mucus coughed up from your respiratory tract. How it works: Your doctor gives you a nebulizer with salt water to help you cough up a sample, says Chupp. Then the sample is tested for the presence of eosinophils. Generally, a sputum eosinophil count of 3 percent or more in a person with severe asthma who experiences persistent flares and symptoms despite using inhalers, would indicate eosinophilic asthma, says Chupp. Important to know: This test is not always practical because some people have trouble generating a sample, he says. However, it’s the most accurate test to confirm a diagnosis of eosinophilic asthma.
Bronchial biopsy
This test is more invasive than the others and less likely to be used for your initial diagnosis. How it works: While you are mildly sedated, a scope is inserted through your nose or mouth to collect tissue from your airways, which is then tested for eosinophils. If eosinophils are detected even though you’ve been treating your asthma with steroids, you may be diagnosed with eosinophilic asthma. Important to know: Most people with asthma will not need this test, but it can be helpful in severe cases, says Chupp. “In our patient population of hundreds of patients, we do these tests maybe a couple times a year,” he says. “It’s usually a very severe case or a case where we’re not really sure if the person has asthma or some other kind of airway disease, and we want to make sure that we’re not missing anything.” For example, a bronchial biopsy might be used to help people with chronic lung or airway infections or those suspected of having an airway disease such as primary ciliary dyskinesia. Your doctor might also recommend an exhaled nitric oxide test, a CT scan, or other lung function tests for additional information.
Your Eosinophilic Test Results: What to Expect Next
If you’re diagnosed with eosinophilic asthma, your doctor might prescribe one of three treatments designed to target eosinophils, says Chupp. These medications, called biologics, can help lower the levels of eosinophils and resulting inflammation in the lungs, which can reduce asthma attacks. Given as injections or infusions you receive every few weeks at your doctor’s office, these therapies work by targeting specific molecules involved in the action of eosinophils. Mepolizumab and reslizumab are antibodies against interleukin 5 (IL-5) molecules, while benralizumab is an antibody against the IL-5-receptor-alpha-chain. Studies suggest that these drugs are safe and effective in most people with eosinophilic asthma, says Chupp. If you have severe or hard-to-treat asthma, talk to your doctor about whether you should be tested for eosinophilia. If you do have eosinophilic asthma, it can affect the type of treatment you’ll need.
