Response to Biologic Therapy in Patients with Asthma and Reduced Pulmonary Diffusion Capacity

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Introduction: Asthma patients with a smoking history are usually excluded from asthma trials to exclude smoking-related comorbidities like chronic obstructive pulmonary disease (COPD). Therefore, little is known about the efficacy of biologic therapy in asthma patients with reduced diffusing capacity of the lungs for carbon monoxide (DLCO). Methods: This study aimed to assess the response to biologic therapy in asthma patients with reduced DLCO. A total of 77 consecutive patients undergoing biologic therapy in a routine clinical setting were included in the analysis and divided into three groups: DLCO ≥60%, DLCO <60% and <10 pack-years, and DLCO <60% and ≥10 pack-years = asthma and COPD comorbidity. Follow-up evaluations were conducted after a minimum of 6 months of therapy. Results: After 34.0 ± 10.2 weeks, comparable therapeutic responses were observed between the three groups. There were no differences between the groups in terms of reduction in the annual acute exacerbation rate (AE median −3 [25th percentile −5; 75th percentile −1] vs. −6.1 [−11.3;−2.2] vs. −3 [−6;−2], p = 0.067), oral corticosteroid (OCS) doses (−5 [−10;0] vs. −1 [−7.5;0] vs. −7.5 [−10;−4] mg, p = 0.136), improvement in Asthma Control Test (ACT) scores (4 [0;9.3] vs. 3 [−1;6] vs. 4 [3;10], p = 0.276) or forced expiratory volume in 1 s (FEV1) improvement (5.5 [−2;21.5] vs. 0.5 [−2.8;9.3] vs. 5 [0;16] % predicted, p = 0.328). Linear regression analysis revealed no significant correlation between DLCO levels and changes in OCS dosage or AE rate, nor between DLCO and improvements in ACT scores or FEV1. Notably, a smaller proportion of patients exhibited a reduced transfer coefficient (DLCO/VA) (n = 13, 16.9%). This parameter did not significantly impact therapy response either. Conclusion: Our findings suggest that biologic therapy can effectively manage asthma irrespective of DLCO measurements. Thus, reduced DLCO values should not preclude thorough asthma diagnosis and treatment. Further investigation into the utility of DLCO/VA assessment in this context is warranted.