Lung function testing in the Top End Health Service (TEHS) region of the Northern Territory has found Indigenous patients have higher levels of airway bronchodilator responsiveness (BDR) than non-Indigenous patients.

While consistent with self-reported symptom-based surveys suggesting higher rates of asthma in the Indigenous population, a significant proportion of Indigenous patients also had evidence of COPD and bronchiectasis.

The study showed evidence of BDR was present in 17% of 742 Indigenous patients and 13% of the 4,579 non-Indigenous patients using the traditional criteria of ≥12% and ≥0.2L change.

Utilising the 2021 updated BDR guidelines, 30% of Indigenous and 20% of non-Indigenous patients fit the BDR criteria (p < 0.001).

The study, published in the Journal of Asthma and Allergy [link here], also found lower post-BD predicted values for FVC and FEV₁, and absolute FEV₁/FVC in the Indigenous group compared to the non-Indigenous group (mean 19%, 22% and 3.4 points lower respectively).

The study also found 46% of the BDR group had radiological evidence of chronic airway diseases such as COPD, bronchiectasis, or both – significantly more compared to the non-BDR group (30%, p = 0.001).

“Spirometry results in 59% (n = 73) of Indigenous and 47% (n = 270) of non-Indigenous patients with BDR demonstrated evidence for a potential diagnosis of COPD (ie, post-BD spirometry FEV₁/FVC ratio <0.7),” the study said.

“However, among the 50 Indigenous patients who did not display spirometric evidence of COPD, 29% (12/42 with radiology) showed evidence of COPD and/or bronchiectasis on radiology.”

“Excluding patients with spirometric or radiographic evidence of COPD or bronchiectasis, 38 (5%) Indigenous patients exhibited BDR, which could be assigned solely to asthma and 308 (7%) non-Indigenous patients.”

The study found increasing age, male sex and current smoking were associated with increased odds of BDR among non-Indigenous patients, while only abnormal radiology was associated with increased odds of BDR in Indigenous patients (OR 1.9, 95% CI 1.23, 2.93).

In both groups of patients obesity was associated with decreased odds of BDR.

The authors, led by Dr Subash Heraganahally from the Royal Darwin Hospital, said theirs was the first study to assess BDR as per the updated 2021 ERS/ATS guidelines in an Indigenous population.

“The findings of our study indicate that among Indigenous Australians, conditions other than asthma or concurrent presence of asthma and COPD, or bronchiectasis alongside asthma could explain the apparently high rates of self-reported asthma in previous population surveys.”

“When excluding the presence of COPD in the present study (via either radiology or spirometry), the prevalence of BDR dropped from 17% to 5% among Indigenous patients and from 13% to 7% among non-Indigenous patients (using the usual/traditional ≥12% and ≥0.2L criteria).”

“This was remarkable given the Indigenous study patients came from a population purported to have a high prevalence of asthma.”

The study concluded that “combining clinical/physical examinations, spirometry and radiology in the accurate diagnosis of airway disease among Indigenous Australians” may have long-term therapeutic implications and lead to overall better outcomes.