Combined ImmunoCAP and Western Blot for the Diagnosis of Aspergillus Lung Disease.

Background: Pulmonary aspergillosis is a major global health concern, yet its diagnosis remains challenging. Aspergillus-specific IgG measurement is essential for identifying chronic and allergic forms.

Objective: This study aimed to evaluate a quantitative method, the ImmunoCAP assay IgG m3 (ICAP) (Phadia-ThermoFisher Scientific, Waltham, USA), a qualitative method, the Aspergillus IgG Western blot kit (Asp-WB) (LDBio Diagnostics, Lyon, France) and a combination of both methods for the diagnosis of Aspergillus lung disease.

Methods: A retrospective study was conducted at the University Hospital of Marseille, France, during 1 year. Patients undergoing Aspergillus serology were divided into three groups: Group 1 (G1) with ICAP ≥ 40 mgA/L and positive Asp-WB, Group 2 (G2) with ICAP ≥ 40 mgA/L and negative Asp-WB and Group 3 (G3) with ICAP < 40 mgA/L and positive Asp-WB. Data were collected on demographics, underlying diseases, imaging and biological outcomes. Patients were classified according to their Aspergillus lung disease, whether acute pulmonary aspergillosis, chronic pulmonary aspergillosis (CPA), allergic broncho-pulmonary aspergillosis (ABPA), colonisation or Aspergillus sensitisation.

Results: A total of 536 patients were studied: 173 in G1, 204 in G2 and 200 in G3, with 38 patients found in several groups. The primary underlying disease was cystic fibrosis in 44.6% of patients. Twenty-two patients were diagnosed with ABPA. The number of diagnosed ABPA cases in G1 (20; 11.6%) combining positive ICAP and Asp-WB was significantly higher than that found in the groups with a single positive test result (p < 0.001). Fifteen patients were diagnosed with CPA. Isolated positive Western blot (G3) identified five cases of aspergilloma. Significantly fewer Aspergillus lung diseases were diagnosed in isolated positive ICAP G2 (8.8%) than in G1 (53.8%) and G3 (42.5%) (p < 0.001).

Conclusions: This study highlights the benefits of combining Asp-WB and ICAP for the diagnosis of Aspergillus lung disease and the relatively high false-positive rate in patients with isolated positive ICAP results.