AbstractBackgroundHigh‐attenuation mucus (HAM) is a specific manifestation of allergic bronchopulmonary mycosis (ABPM) on chest computed tomography (CT).ObjectivesTo compare the diagnostic accuracy of the two definitions of HAM and to clarify the clinical and radiographic characteristics of HAM‐positive and HAM‐negative ABPM.MethodsCT images at the diagnosis of ABPM using Asano's criteria were retrospectively analysed. In Study #1, radiographic data obtained using the same CT apparatus in a single institute were analysed to determine the agreement between the two definitions of HAM: a mucus plug that is visually denser than the paraspinal muscles or that with a radiodensity ≥70 Hounsfield units. In Study #2, HAM was diagnosed by comparison with the paraspinal muscles in patients with ABPM reporting to 14 medical institutes in Japan.ResultsIn Study #1, 93 mucus plugs from 26 patients were analysed. A substantial agreement for HAM diagnosis was observed between the two methods, with a κ coefficient of 0.72. In Study #2, 60 cases of ABPM were analysed; mucus plugs were present in all cases and HAM was diagnosed in 45 (75%) cases. The median A. fumigatus‐specific IgE titre was significantly lower in HAM‐positive patients than in HAM‐negative patients (2.5 vs. 24.3 UA/mL, p = .004). Nodular shadows were observed more frequently in the airways distal to HAM than in those distal to non‐HAM mucus plugs (59% vs. 32%, p < .001).ConclusionIn conclusion, agreement between the two methods to diagnose HAM was substantial. HAM was associated with some immunological and radiographic characteristics, including lower levels of sensitization to A. fumigatus and the presence of distal airway lesions.