Eosinophilic asthma is a specific type of asthma characterized by airway inflammation driven by elevated levels of white blood cells called eosinophils. This form often presents as severe and can be challenging to manage with standard treatments. Accurate diagnosis is important as it guides healthcare providers toward targeted therapies, improving symptom control and quality of life. The diagnostic process involves specific steps to identify this inflammatory pathway.
What Makes Eosinophilic Asthma Different
Eosinophilic asthma stands apart from other asthma types due to its underlying biological mechanism. An excessive presence of eosinophils, a type of white blood cell, contributes to airway inflammation. These cells, while normally fighting infections, release substances that cause swelling and damage in the respiratory system. This eosinophil-driven inflammation is distinct from other asthma phenotypes, such as allergic asthma, where triggers like pollen primarily drive the immune response. The unique inflammatory profile often means it does not respond well to conventional inhaled corticosteroids, highlighting the importance of identifying this specific subtype for appropriate treatment.
General Asthma Diagnosis Steps
Before considering eosinophilic asthma, a general diagnosis of asthma is typically established through a comprehensive evaluation. This process begins with a detailed review of a patient’s medical history and current symptoms. Healthcare providers inquire about common asthma symptoms such as chronic cough, wheezing, shortness of breath, and chest tightness, noting their frequency, intensity, and any specific triggers. A physical examination is also performed, including listening to the chest for wheezing and examining the nose and throat for signs of related conditions.
Pulmonary function tests objectively assess lung function. Spirometry measures how much air a person can exhale after a deep breath and how quickly they can breathe it out. If spirometry indicates airway obstruction, the test may be repeated after administering a bronchodilator; significant improvement suggests asthma. Peak flow tests, which measure how fast air can be blown out, may also track lung function variability. These foundational steps are important for confirming an asthma diagnosis before investigating an eosinophilic component.
Targeted Tests for Eosinophilic Markers
Once a general asthma diagnosis is established, specific tests identify the presence and extent of eosinophilic inflammation. These targeted tests help determine if eosinophils are a significant driver of the patient’s asthma. No single test is definitive; results are interpreted in conjunction with the patient’s clinical picture.
The blood eosinophil count measures the number of eosinophils circulating in the blood. An elevated count, typically above 150 cells/µL or over 300 cells/µL, can suggest eosinophilic asthma. While easy to obtain, this count alone does not definitively diagnose eosinophilic asthma, as other conditions can also cause elevated levels. Results are interpreted in the context of the patient’s overall health and symptoms.
The sputum eosinophil count is performed on a sample of mucus coughed up from the respiratory tract. This test directly measures airway inflammation. A finding of more than 2-3% eosinophils in the sputum suggests eosinophilic asthma. It provides a direct look at the inflammatory cells present in the airways, making it a valuable tool for diagnosis and monitoring.
The Fractional Exhaled Nitric Oxide (FeNO) test measures nitric oxide gas in exhaled breath. Nitric oxide is produced by cells involved in eosinophil-associated airway inflammation. Elevated FeNO levels, typically above 50 parts per billion (ppb) in adults, indicate significant eosinophilic airway inflammation. This non-invasive test helps assess inflammation and monitor response to corticosteroid treatment.
Making the Eosinophilic Asthma Diagnosis
Diagnosing eosinophilic asthma involves synthesizing information from the patient’s symptoms, medical history, general asthma tests, and specific eosinophilic marker tests. Healthcare providers consider clinical features, such as persistent, difficult-to-control asthma symptoms, alongside objective test results. Poor response to conventional inhaled corticosteroid therapy, chronic rhinosinusitis, and nasal polyps are often seen in individuals with eosinophilic asthma.
No single test result confirms the diagnosis; it is a comprehensive assessment. Elevated blood eosinophil counts, high sputum eosinophil levels, and increased FeNO readings collectively point towards eosinophilic inflammation as the primary driver of asthma. The diagnostic process also involves ruling out other conditions that might present with similar respiratory symptoms. This thorough approach ensures an accurate diagnosis, guiding treatment decisions. Identifying eosinophilic asthma allows for the selection of targeted therapies, such as biologic medications, that specifically address the underlying eosinophilic inflammation, leading to more effective management.