Aspergillus-specific IgG antibodies for diagnosing chronic pulmonary aspergillosis compared to the reference standard

OBJECTIVES

To evaluate the performance of Aspergillus-specific IgG antibodies for diagnosing chronic pulmonary aspergillosis (CPA) by using a cohort of patients with histologically proven CPA as a reference standard.

METHODS

We collected Aspergillus-specific IgG antibody titres from patients with histologically proven CPA in collaboration with CPAnet study sites in Denmark, Germany, Belgium, India, Moldova, and Pakistan (N = 47). Additionally, sera from diseased and healthy controls were prospectively collected at the Medical Clinic of the Research Center, Borstel, Germany (n = 303). Aspergillus-specific IgG antibody titres were measured by the ImmunoCAP® assay (Phadia 100, Thermo Fisher Scientific, Uppsala, Sweden). An Aspergillus-specific IgG antibody titre ≥50 mgA/L was considered positive.

RESULTS

Using patients with histologically proven CPA as the reference standard, the ImmunoCAP® Aspergillus-specific IgG antibody test had a sensitivity and specificity of 85.1% (95% CI: 71.7-93.8%) and 83.6% (95% CI: 78.0-88.3%), respectively. Patients with histologically proven CPA had significantly higher Aspergillus-specific IgG antibody titre with a median of 83.45 mgA/L (interquartile range 38.9-115.5) than all other cohorts (p < 0.001). False-positive test results occurred in one-third of 79 healthy controls.

DISCUSSION

Our study results confirm a high sensitivity of the Aspergillus-specific IgG antibody test for the diagnosis of CPA when using patients with histologically proven CPA as a reference standard. However, positive test results should always match radiological findings as false-positive test results limit the interpretation of the test.

The clinical value of Aspergillus-specific IgG antibody test in the diagnosis of nonneutropenic invasive pulmonary aspergillosis

OBJECTIVES

Aspergillus-specific IgG antibody (Asp IgG) has been successfully applied in the diagnosis of chronic pulmonary aspergillosis. We explored its value in nonneutropenic invasive pulmonary aspergillosis (IPA) by a multicenter, prospective, and controlled study.

METHODS

We enrolled 372 clinically suspected nonneutropenic patients with IPA from February 2015 to August 2022. After excluding 4 cases with Aspergillus colonization, the remaining 368 cases were finally confirmed as patients with IPA (n = 99), or non-IPA patients (n = 269) consisting of community-acquired pneumonia (n = 206), tuberculosis (n = 22), nontuberculous mycobacteria (n = 5), lung abscess (n = 6), or noninfectious diseases (n = 30). Asp IgG in plasma samples was tested by enzyme-linked immunosorbent assay.

RESULTS

At cut-off value of ≥80 AU/mL, Asp IgG had much higher sensitivity (59.6% vs. 19.2%, p < 0.0001), but lower specificity (77.0% vs. 96.3%, p < 0.0001) than serum galactomannan (GM) (cut-off value of ≥1.0), and similar sensitivity (59.6% vs. 55.6%, p = 0.611) but lower specificity (77.0% vs. 91.2%, p = 0.001) than bronchoalveolar lavage fluid (BALF) GM (cut-off value of ≥1.0), respectively. Combination diagnosis of either positive for Asp IgG or BALF GM had higher sensitivity (81.0% vs. 55.6%, p = 0.002), but lower specificity (75.2% vs. 91.2%, p = 0.001) than BALF GM alone. The receiver operating characteristic curve showed that Asp IgG had an optimal diagnostic value when the cut-off value was 56.6 AU/ml, and the sensitivity and specificity were 77.8% and 63.9%, respectively.

DISCUSSIONS

The diagnostic value of Asp IgG for IPA is superior to serum GM, and a little inferior to BALF GM in nonneutropenic patients with IPA. Considering the convenience of taking blood samples, it is a good screening and diagnostic method for nonneutropenic patients with IPA, especially for those who cannot bear invasive procedures.

Prospective study of the serum Aspergillus-specific IgG, IgA and IgM assays for chronic pulmonary aspergillosis diagnosis

Background

Chronic pulmonary aspergillosis (CPA) is an underdiagnosed and misdiagnosed disease and now increasingly recognised. However, the diagnosis of CPA remains challenging. In this study, we aimed to investigate the diagnostic values of serum Aspergillus-specific IgG, IgA and IgM antibodies in patients with CPA.

Methods

The prospective study was performed at Chinese People’s Liberation Army General Hospital in Beijing, from January 2017 to December 2017. Adult patients with lung lesions presented as cavity, nodule, mass, bronchiectasis or severe fibrotic destruction with at least two lobes in CT imaging were enrolled. One hundred healthy persons were also enrolled as additional controls. The serum levels of Aspergillus-specific IgG, IgA and IgM antibodies and galactomannan (GM) levels were measured simultaneously by plate ELISA kit.

Results

A total of 202 patients were enrolled in this study, including 42 CPA patients, 60 non-CPA patients and 100 healthy persons. The most common underlying lung diseases in CPA patients were bronchiectasis (28.6%) and COPD (19.0%). The most common symptoms in the CPA patients were cough (76.2%), sputum (71.4%), and fever (45.2%); chest pain (4.8%) was infrequent. Receiver operating characteristic (ROC) curve analysis revealed that the optimal CPA diagnostic cut-off of Aspergillus-specific IgG, IgA and IgM assays and GM test were 89.3 AU/mL, 8.2 U/mL, 73.3 AU/mL and 0.5μg/L, respectively. The serum levels of Aspergillus-specific IgG and IgA in CPA patients were higher than these in non-CPA patients or healthy persons. The sensitivities and specificities of Aspergillus-specific IgG, IgA, IgM tests and GM test were 78.6 and 94.4%, 64.3 and 89.4%, 50.0 and 53.7% and 71.4 and 58.1%, respectively.

Conclusions

The sensitivity and specificity of serum Aspergillus-specific IgG assay are satisfactory for diagnosing CPA, while the performance of Aspergillus-specific IgA assay is moderate. Aspergillus-specific IgM assay and serum GM test have limited value for CPA diagnosis.

Trial registration

NCT03027089. Registered 20 January 2017.