Aspergillosis serology for the diagnosis of chronic pulmonary aspergillosis: evaluation of Western Blot and ELISA with an optimized threshold

Author:

Jeanne Bigot (FR)

Abstract:

Background:
The diagnostic criteria of chronic pulmonary aspergillosis (CPA) encompass clinical, radiological, and mycological domains. Testing for anti-Aspergillus antibodies is one of the key diagnostic tools for the CPA diagnosis. In France, it is common that anti-Aspergillus IgG levels are measured using an ELISA method and their presence is confirmed through the detection of precipitins via immuno-electrophoresis (IEP). This latter technique is time-consuming and challenging to interpret. In addition, laboratories now face to discontinuation in reagents needed for IEP. Therefore, we aimed to assess new serological approaches exhibiting high sensitivity and specificity for CPA diagnosis.
Methods:
On the one hand, we selected 54 sera collected from patients with a definitive diagnosis of CPA (positive serology with ELISA (Platelia A. fumigatus, BioRad, Marnes la Coquette, France) confirmed with IEP (homemade technique using Microgen FSK Aspergillus antigen; n=25), asymptomatic pregnant women (n=5), patients with an A. fumigatus (A.f) contamination in their respiratory samples (n=5), and patients chronically colonized with A.f but after ruling out CPA diagnosis (n=19)). All those sera were tested with a Western Blot technique commercially available (LDBio, Lyon, France). Results for CPA patients were compared to those obtained from all other patients (negative control group). On the other hand, we selected ELISA results for 35 sera obtained from 35 CPA patients and for 100 sera from control patients in whom CPA was suspected but ruled out, for a Receiving Operating Curve analysis.
Results:
The Western Blot demonstrated a sensitivity and a specificity of 88% and 41%, respectively. Indeed we observed false positives with this technique in colonization and contamination group (n=12/19 and 5/5 respectively) by not in pregnant women. Using a threshold of 25 UA/mL offers the best sensitivity and specificity, i.e., 97% (85,47% – 99,85%) and 97% (91,55% – 99,18%) respectively, against 94% and 87% with the threshold recommended by the manufacturer (10 UA/mL.
Conclusions:
In conclusion, our results indicate that Western Blot lacks specificity for the diagnosis of CPA when colonized patients and patients with A.f contamination are included in control group. In contrast, the analytical performance of the ELISA technique is excellent when increasing the threshold of positivity from 10 to 25 UA/mL.

Abstract Number: 30

Conference Year: 2024

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