Abstract
The currently prescribed tests for asthma diagnosis require compulsory patient compliance, and are usually not sensitive to mild asthma. Development of an objective test using minimally invasive samples for diagnosing and monitoring of the response of asthma may help better management of the disease. Raman spectroscopy (RS) has previously shown potential in several biomedical applications, including pharmacology and forensics. In this study, we have explored the feasibility of detecting asthma and determining treatment response in asthma patients, through RS of serum. Serum samples from 44 asthma subjects of different grades (mild, moderate, treated severe and untreated severe) and from 15 reference subjects were subjected to Raman spectroscopic analysis and YKL-40 measurements. The force expiratory volume in 1 second (FEV1) values were used as gold standard and the serum YKL-40 levels were used as an additional parameter for diagnosing the different grades of asthma. For spectral acquisition, serum was placed on a calcium fluoride (CaF2) window and spectra were recorded using Raman microprobe. Mean and difference spectra comparisons indicated significant differences between asthma and reference spectra. Differences like changes in protein structure, increase in DNA specific bands and increased glycosaminoglycans-like features were more prominent with increase in asthma severity. Multivariate tools using Principal-component-analysis (PCA) and Principal-component based-linear-discriminant analysis (PC-LDA) followed by Leave-one-out-cross-validation (LOOCV), were employed for data analyses. PCA and PC-LDA results indicate separation of all asthma groups from the reference group, with minor overlap (19.4%) between reference and mild groups. No overlap was observed between the treated severe and untreated severe groups, indicating that patient response to treatment could be determined. Overall promising results were obtained, and a large scale validation study on random subjects is warranted before the routine clinical usage of this technique.
Highlights
Asthma is a chronic inflammatory disorder of the airways characterized by airway hyper-responsiveness (AHR) and reversible airflow obstruction that fluctuates over time [1]
Such an approach could serve as an objective method for asthma diagnosis for all patients and could enable “distance diagnosis” where the samples could be transported to a centralized facility for analyses
No statistically significant difference in YKL-40 levels was observed between the controls and the treated severe group (p-value = 0.2918)
Summary
Asthma is a chronic inflammatory disorder of the airways characterized by airway hyper-responsiveness (AHR) and reversible airflow obstruction that fluctuates over time [1]. New international guidelines recommend the measurement of serial peak expiratory flows, spirometry or bronchoprovocation to confirm the diagnosis of asthma [9,10,11] These are primarily based on demonstrating abnormal airway physiology, which may not always be present in mild asthma, leading to a decreased sensitivity. In light of need for better diagnostic tools with attributes like rapidity, objectivity and the use of minimally invasive samples, RS could serve useful for detection of asthma. This pilot study was carried out to explore the potential applicability of RS in detecting disease-related perturbations in serum of mild, moderate and severe asthma as well as reference subjects. The serum YKL-40 level was measured and the estimated levels were used as an additional parameter to confirm the clinical status of all subjects
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