Correlation of spirometry indices to chest radiology in the diagnosis of chronic airway disease among regional and rural Indigenous Australians

Background: The majority of Indigenous Australians reside in non-urban locations, with reduced access to chest radiology such as computed tomography (CT). Spirometry and chest X-ray (CXR) may be used in the absence of CT; however, the correlation of spirometry indices to CT-defined chronic airway diseases (i.e. chronic obstructive pulmonary disease (COPD) and bronchiectasis) compared with CXR among Indigenous people is sparsely reported. Aim: To evaluate spirometry indices against CXR and CT findings among adult Indigenous Australians. Methods: Indigenous patients who had undergone a spirometry test between 2012 and 2020 and had a CXR or chest CT scan assessed for the presence (⁺)/absence (⁻) of airway diseases were included in this study. Results: Of 643 patients (57% female, 31% remote/very remote), 364 (57%) had CT and CXR available. Patients who were ‘CT⁻ and CXR⁻’ for airway diseases (48%) recorded a mean FVC, FEV₁ and FEV₁/FVC of 61%, 59% and 0.76 compared to 57%, 49% and 0.66 in the ‘CT⁺ and CXR⁻’ group and 53%, 39% and 0.58 in the ‘CT⁺ and CXR⁺’ group. CXR showed sensitivity (44%) and specificity (88%), while spirometry showed 62% and 77% compared to CT. Spirometry demonstrated predominately restrictive impairment among ‘CT⁻ and CXR⁻’ and mixed/obstructive impairment among ‘CT⁺ and CXR⁻’ and ‘CT⁺ and CXR⁺’ groups. Conclusion: Indigenous Australians tend to demonstrate restrictive impairment in the absence of radiological evidence of airway disease. However, in the presence of airway disease, combinations of mixed and obstructive impairments were common. Obstructive impairment shows greater sensitivity for identifying COPD than that shown by CXR; however, CXR shows greater specificity. Hence, spirometry in conjunction with chest radiology should be utilised to aid in the assessment of airway diseases in this population.