Our eosinophilosophy
eos counts in
other lung conditions

There are several lung conditions in addition to severe eosinophilic asthma in which

eosinophils play an important role, including1,2:

Eosinophilic pneumonia

Eosinophilic pneumonia is considered a primary eosinophilic lung disease that is limited to the lung.1,3 The disease consists of both acute and chronic conditions in which eosinophils infiltrate the lung. The two forms of pneumonia differ with regard to cause, onset, and course of disease.3


Acute eosinophilic pneumonia is a rare eosinophilic lung disease with an estimated 9.1 cases per 100,000 patient-years. The disease tends to occur more in males than females, and patients are often in their 20s. A history of smoking is common in patients with acute eosinophilic pneumonia.3 The onset of pneumonia occurs within days and may be associated with a change in smoking habits, such as restarting smoking, increasing cigarette number, or recently starting smoking.1,3

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Role of eosinophils in acute eosinophilic pneumonia

Although the exact cause of acute eosinophilic pneumonia is unknown, eosinophil activation and recruitment to the lung is thought to occur via T helper 2 (Th2) cell- and group 2 innate lymphoid 2 (ILC2)-mediated immune responses following alveolar or airway epithelial damage from an inhaled antigen. The damage can lead to secretion of interleukin 25 (IL-25), IL-33, and thymic stromal lymphopoietin (TSLP), polarizing Th2 cells and stimulating ILC2. IL-33 is thought to play an important role in this condition, and elevated levels of IL-33, IL-8, and IL-5 have been found in the blood and bronchoalveolar lavage (BAL) fluid in patients.3

EOS counts in acute eosinophilic pneumonia diagnosis

Greater than 25% of eosinophils in BAL fluid is key to establishing a diagnosis¹
Greater than 25% of eosinophils in BAL fluid is key to establishing a diagnosis¹

Modified Philit criteria used for eosinophilic pneumonia diagnosis include1,3:

  • BAL fluid eosinophils >25% and/or lung biopsy showing eosinophil infiltration of the lung parenchyma
  • Diffuse pulmonary infiltrates (bilateral)
  • Hypoxemia
  • Acute febrile illness of <1 month
  • No known cause of eosinophilic lung disease

Although these criteria are used in diagnosis, there are no formal diagnostic criterion for acute eosinophilic pneumonia3

Blood eosinophilia (>500 cells/µL) in acute eosinophilic pneumonia is rare.3


Chronic eosinophilic pneumonia is a rare eosinophilic lung disease with a reported incidence in the US of 0.5-1.2%. The disease affects females more than males, and the age range of patients tends to be from 30 to 50, although any age can be affected.3 Patients with chronic eosinophilic pneumonia often have a history of asthma and allergies. Patients typically have BAL and blood eosinophilia in addition to elevated immunoglobulin E (IgE).1,3

Clinical manifestations of chronic eosinophilic pneumonia include1,3:

  • Prolonged respiratory symptoms (respiratory failure is rare)
    • Dyspnea
    • Cough
    • Wheezing
    • Sputum
  • Mild hypoxemia or normal blood oxygen
  • Low-grade fever
  • Loss of appetite and weight loss

EOS counts in chronic eosinophilic pneumonia diagnosis

Greater than 25% of eosinophils in BAL and/or 30% of eosinophils of total white blood cells

Criteria for chronic eosinophilic pneumonia diagnosis include1,3:

  • Respiratory symptom duration >2 weeks
  • Chest radiograph showing pulmonary infiltrates
    • Infiltrates often have a peripheral predominance
  • BAL eosinophilia typically >25%
  • Blood eosinophilia (often >30% of white blood cells) and/or evidence of eosinophil infiltration of lungs
  • Exclusion of other eosinophilic lung diseases such as ABPA or eosinophilic granulomatosis with polyangiitis (EGPA)

Could it be HES or EGPA?

Chronic eosinophilic pneumonia can have uncommon non-respiratory manifestations (arthralgias, neuropathy, skin, and gastrointestinal symptoms) in addition to pulmonary infiltrates and eosinophilia. Also, patients often have a history of allergies and asthma; therefore, differentiating among chronic eosinophilic pneumonia, hypereosinophilic syndrome (HES), and EGPA in some cases may be challenging.1

Allergic bronchopulmonary aspergillosis

ABPA is an eosinophilic lung condition caused by a hypersensitivity reaction to fungus Aspergillus fumigatus, typically occurring in patients with asthma or cystic fibrosis.1,4,5 ABPA is a subset of allergic bronchopulmonary mycosis (ABPM) and includes hypersensitivity reactions to Aspergillus fumigatus, other Aspergillus species, and other filamentous fungi.4,6 Prevalence of ABPA is estimated to be approximately 1-2% in patients with asthma, and approximately 8-10% in patients with cystic fibrosis.5

EOS counts in ABPA diagnosis

Greater than or equal to 500 cells/µL for blood eosinophils

Diagnostic criteria for ABPA/ABPM without cystic fibrosis4

Patients must meet 6 or more of the following 10 criterion for diagnosis of ABPA/ABPM:

  • Asthma or history of asthma
  • Blood eosinophilia (≥500 cells/µL)
  • Elevated serum IgE (≥417 IU/mL)
  • Specific IgE for filamentous fungi* or immediate cutaneous hypersensitivity to filamentous fungi on skin test*
  • Specific IgG or precipitins for filamentous fungi*
  • Filamentous growth in BAL or sputum cultures*
  • Presence of mucus plugs in central bronchi
    • History of mucus plug expectoration, or seen on computed tomography (CT) scan or bronchoscopy
  • Fungal hyphae in bronchial mucus plugs
  • CT imaging showing high attenuation mucus in the bronchi
  • Central bronchiectasis on CT

*Fungi should be identical

Early diagnosis and treatment of ABPA/ABPM is important for
prevention of long-term tissue damage6

Chronic obstructive pulmonary disease

COPD is a respiratory disease characterized by airflow limitation and persistent respiratory symptoms including dyspnea, cough, and sputum production. Airflow limitation in COPD is due to airway and/or alveolar abnormalities, which are often a result of marked exposure to noxious gases or particles, with tobacco smoking being the main risk factor. US prevalence is estimated at less than 6% of the adult population.2

Eosinophils icon

Eosinophilic inflammation can occur in COPD

Blood eosinophils are elevated in some patients with COPD. Increased eosinophils in these patients can lead to the release of inflammatory mediators. Some studies show increased risk of exacerbations in patients with elevated blood eosinophil levels; however, other studies show no relationship.2

EOS counts in
COPD treatment considerations

Greater than 300 eosinophils/µL

Blood eosinophil levels provide guidance for the use of inhaled corticosteroids (ICS) to help prevent exacerbations. Several studies have shown that blood eosinophil counts help predict how well adding ICS to bronchodilator therapy will help prevent exacerbations.2,7 ICS has little to no effect in patients with COPD with lower eosinophil counts of <100 cells/μL.2

Counts of >300 cells/μL can be used to identify patients who
will benefit the most from adding ICS to their bronchodilator

Less than 2% of eosinophils in white blood cell count

Patients with blood eosinophils <2% were found to have an increased risk of developing pneumonia, therefore, this threshold may also be considered in treatment decisions.2

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  1. Wechsler ME. Pulmonary eosinophilic syndromes. Immunol Allergy Clin North Am. 2007;27(3):477-492.
  2. Global Initiative for Chronic Obstructive Lung Disease (GOLD). Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease. 2021 report. https://goldcopd.org/2021-gold-reports/. Accessed June 6, 2021.
  3. Suzuki Y, Suda T. Eosinophilic pneumonia: A review of the previous literature, causes, diagnosis, and management. Allergol Int. 2019;68(4):413-419.
  4. Asano K, Hebisawa A, Ishiguro T, et al. New clinical diagnostic criteria for allergic bronchopulmonary aspergillosis/mycosis and its validation. J Allergy Clin Immunol. 2021;147(4):1261-1268.e5.
  5. Vitte J, Ranque S, Carsin A, et al. Multivariate analysis as a support for diagnostic flowcharts in allergic bronchopulmonary aspergillosis: A Proof-of-Concept Study. Front Immunol. 2017;8:1019.
  6. Fukutomi Y, Tanimoto H, Yasueda H, Taniguchi M. Serological diagnosis of allergic bronchopulmonary mycosis: Progress and challenges. Allergol Int. 2016;65(1):30-36.
  7. Global Initiative for Asthma (GINA). Global strategy for asthma management and prevention. 2021 main report. https://ginasthma.org/gina-reports/. Accessed June 6, 2021.