Sputum Neutrophil Gelatinase-Associated Lipocalin as a Biomarker in Asthma-COPD Overlap

Asthma COPD overlap (ACO) is a consensus-based phenotype having characteristics of both COPD and asthma. Distinguishing ACO from other diseases is even more important as it is related to low health-related quality of life, augmented exacerbation rate and hospital admission, a rapid deterioration in lung function, and increased morbidity and mortality. But it cannot be diagnosed explicitly based on spirometry tests, patient demographics, radiology, or by-sputum cytology. There is an unmet need to develop biomarkers.

To assess the role of sputum neutrophil gelatinase-associated lipocalin (NGAL) as a biomarker of ACO. To find the correlation between sputum NGAL levels with forced expiratory volume 1 (FEV1) and exacerbation rate in ACO. To find the correlation between sputum NGAL level with sputum neutrophils and eosinophils in ACO.

In this comparative correlational study, 180 subjects were enrolled into four groups with 45 patients each with asthma, COPD, ACO, and healthy nonsmokers respectively, respectively. After taking detailed history and demographics, sputum was analyzed for the differential count and NGAL.

Asthma COPD overlap (ACO) cases had high sputum NGAL levels; the second was the COPD group, and the last in the case asthma group. Nonsmokers had notably lower readings than the diseased. Out of three, receiver operating characteristic (ROC) figures, the validity of NGAL was best in selecting patients of ACO than COPD and asthma. The area under curve (AUC) was highest for ACO and less than the acceptable limit for the remaining two. NGAL cut-off value of 2473 pg/mL had 80% sensitivity and 50% specificity for ACO.

The present study investigated the sputum NGAL levels as a biomarker in ACO identified by the syndromic approach. Sputum NGAL, a biomarker associated with airway inflammation in airway diseases, was supportive of clinically differentiating ACO from asthma to COPD. How to cite this article: Babu A, Narayanswamy H, Baburao A. Sputum Neutrophil Gelatinase-Associated Lipocalin as a Biomarker in Asthma-COPD Overlap. J Assoc Physicians India 2023;71(9):34-38.