Aspergillus Fumigatus IgG Level Greater Than 60 Mg/l Increases Diagnostic Specificity of Allergic Bronchopulmonary Aspergillosis

The Modified ISHAM (International Society for Human and Animal Mycology) working group 2013 criteria for diagnosis of allergic bronchopulmonary aspergillosis (ABPA) does not specify a cut-off value for specific IgG anti-Aspergillus fumigatus. Case notes of 80 patients (all with severe asthma and peripheral blood eosinophilia >500/ul) suspected of ABPA were retrospectively analyzed. Total IgE, specific IgE (m3IgE) and specific IgG Aspergillus fumigatus (Gm3) were measured using ImmunoCAP. Patients were assigned into 3 groups based on Modified ISHAM criteria: definite, possible, not ABPA. Gm3 levels were excluded at this assignment. Of 80 patients (48 male, age range 19-86 years), 30 (37.5%) had positive specific IgE against Aspergillus fumigatus (>0.35kUA/L). 13 patients had ‘definite’ ABPA, 15 ‘possible’ and 52 ‘not ABPA’ group. Median total IgE levels of patients with definite and possible ABPA were 2144kU/L and 2597kU/L respectively (non-signifcant), while median m3IgE levels were 4.35kUA/L and 1.47kUA/L (p<0.05). Mean Gm3 levels compared using ANOVA (Statgraphics Centurion Professional XV, Statpoint Inc) showed a significant difference between definite and other groups (p<0.001), that was confirmed using multiple range tests (Fisher's least significant difference procedure). Mean Gm3 level in definite ABPA was 125.17mgA/L (±SD 54.84, 95%CI 92.03-158.32), while mean Gm3 levels in possible and not ABPA were 18.61mgA/L and 30.05mgA/L respectively. Sensitivity for definite ABPA was 69% and 85% using 90mgA/L and 60mgA/L, with specificity 100% for both. Positive Gm3 supports a diagnosis of ABPA but low level false positives are common. Using a higher cut-off of 60mgA/L gave good sensitivity while maintaining excellent specificity.