Allergic bronchopulmonary aspergillosis (ABPA) is a condition characterised by an exaggerated response of the immune system (a hypersensitivity response) to the fungus Aspergillus (most commonly Aspergillus fumigatus). It occurs most often in people with asthma or cystic fibrosis. Aspergillus spores are ubiquitous in soil and are commonly found in the sputum of healthy individuals. A. fumigatus is responsible for a spectrum of lung diseases known as aspergilloses. ABPA causes airway inflammation, leading to bronchiectasis—a condition marked by abnormal dilation of the airways. Left untreated, the immune system and fungal spores can damage sensitive lung tissues and lead to scarring. The exact criteria for the diagnosis of ABPA are not agreed upon. Chest X-rays and CT scans, raised blood levels of IgE and eosinophils, immunological tests for Aspergillus together with sputum staining and sputum cultures can be useful. Treatment consists of corticosteroids and antifungal medications. Signs and symptoms
Almost all patients have clinically diagnosed asthma, and present with wheezing (usually episodic in nature), coughing, shortness of breath and exercise intolerance (especially in patients with cystic fibrosis). Moderate and severe cases have symptoms suggestive of bronchiectasis, in particular thick sputum production (often containing brown mucus plugs), as well as symptoms mirroring recurrent infection such as pleuritic chest pain and fever. Patients with asthma and symptoms of ongoing infection, who do not respond to antibiotic treatment, should be suspected of ABPA. Pathophysiology
Aspergillus spores are small (2–3 μm in diameter) and can penetrate deep into the respiratory system to the alveolar level.
A raised IgE increases suspicion, though there is no universally accepted cut-off value. Values can be stated in international units (IU/mL) or ng/mL, where 1 IU is equal to 2.4 ng/mL. Since studies began documenting IgE levels in ABPA during the 1970s, various cut-offs between 833 and 1000 IU/mL have been employed to both exclude ABPA and to warrant further serological testing. The current consensus is that a cut-off of 1000 IU/mL should be employed, as lower values are encountered in SAFS and asthmatic sensitization.IgG antibody precipitin testing from serum is useful, as positive results are found in between 69 and 90% of patients, though also in 10% of asthmatics with and without SAFS. Therefore, it must be used in conjunction with other tests. Various forms exist, including enzyme-linked immunosorbent assay (ELISA) and fluorescent enzyme immunoassay (FEIA). Both are more sensitive than conventional counterimmunoelectrophoresis. IgG may not be entirely specific for ABPA, as high levels are also found in chronic pulmonary aspergillosis (CPA) alongside more severe radiological findings.Until recently, peripheral eosinophilia (high eosinophil counts) was considered partly indicative of ABPA. More recent studies show that only 40% of people with ABPA  present with eosinophilia, and hence a low eosinophil count does not necessarily exclude ABPA; for example patients undergoing steroid therapy have lower eosinophil counts. Radiological investigation
Consolidation and mucoid impaction are the most commonly described radiological features described in ABPA literature, though much of the evidence for consolidation comes from before the development of computed tomography (CT) scans.