Background
Chronic cough was a common complaint of patients in respiratory clinics, which was involved in many conditions, such as cough variant asthma, eosinophilic bronchitis, atopic cough, upper airway cough syndrome and gastro-oesophageal acid reflux disease [
1,
2]. The global prevalence of chronic cough was up to 9.6% in general adult populations [
3]. Chronic cough could cause significant physical, psychological and social morbidity. Besides routine clinical evaluations, reliable and valid evaluation on the impact of cough on their health status is an important step in management of the patients. An ideal measure for chronic cough should include information on cough severity, social and psychological aspects of patients and promote communication between patient and clinician. A few measurements have been used in clinical practice and clinical trials. Cough Symptom Score (CSS) was a simple two-part questionnaire relating to cough symptoms [
4], which is focused on cough frequency, and overall impact on daily life. However, CSS is not easy to distinguish the different score level based on cough numbers, and there was little clinical experience with this tool. Cough Visual Analog Scales (VAS) is a brief subjective assessment of cough severity, but lost sight of other aspects of cough-impact on health. Available cough-specific health status measures, such as the Leicester Cough Questionnaire (LCQ) [
5], and Cough-Specific Quality of-Life Questionnaire (CQLQ) [
6], were reliable, valid, widely used in clinical trials. It takes more than 5 min to complete and calculate score of CQLQ with 28 items in six domains, and it needs scoring algorithms to calculate scores of each domain and total score of LCQ with 19 items in three domains, which makes these questionnaires are time-consuming and complex to use in clinical practice. There is a lack of a simple, effective method to assess different aspects of chronic cough in routine care [
7,
8]. Therefore, we aim to develop a new simple measurement for chronic cough, Cough Evaluation Test (CET), including physical, psychological and social aspects.
Discussion
This study has created a short, simple patient-completed test for chronic cough patients with good measurement properties. Almost all patients could complete the CET within 1 minute in this study. The 5 items selected for CET parallel the dimensions of cough management—cough severity, social impact and psychological effect. In this study, scores computed from CET were shown to be highly repeatable and responsive, suggesting CET may be a useful outcome measure in assessing the response to intervention in clinical practices and trials.
Cronbach’s alpha coefficient of CET was 0.80, which was sufficient in internal consistency. No matter at baseline or after treatment, CET has shown a strong correlation with cough VAS and LCQ-MC, and its correlation intensity were significantly higher than that between cough VAS and LCQ-MC, and were also higher than those between cough VAS or LCQ-MC and other measures, indicating CET was useful to assess cough severity and cough-related quality of life. Although intraclass correlation coefficient of LCQ-CM was lower than that in the previous researches (0.89–0.96) [
5,
9,
10], but it still has excellent level of repeatability. The intraclass correlation coefficient of cough VAS (0.85) was almost the same as Birring’s data (0.84) [
5], indicating VAS also has a stable and excellent test-retest reliability. In addition, CET has the same excellent degree of test-retest reliability as LCQ-MC and cough VSA did, and Bland-Altman plot of CET also showed its excellent repeatability.
Our data also showed that the CET was responsive to change after treatment and the effect size was less than that seen with the cough VAS, but was more than that seen with LCQ-MC. Cohen proposed benchmarks that serve to guide the interpretation of effect sizes: 0.2 for ‘small’ effects, 0.5 for ‘medium’ effects, and 0.8 for ‘large’ effects [
15]. In our study, CET and cough VAS can detect “large” effects, while LCQ-MC can just reflect the “medium” effect after the treatment, suggesting that CET and cough VAS might be better outcome measures of choice in clinical trials. The effect size represents individual change in terms of the number of pre-test SD, which mean that characteristics of the distribution, particularly at baseline, may strongly influence the effect size [
13]. And it could explain why effect sizes in our data were less than that in Birring’ result [
5].
More than 80% of cough occurs during awake time [
16], while some patients like cough variant asthma may also suffer from nocturnal cough. One direct effect of nocturnal cough was sleep disturbance. Moreover, cough intensity was also an important determinant of cough severity in some patients [
16,
17]. Three items of CET including “How frequently did you cough during the day?”, “Have your cough disturbed your sleep?”, “Did you have intense cough?” correspond to cough severity that was a single concept with three inter-related components: frequency, intensity, and disruption [
18]. Cough is protective reflex. Some smokers may cough a lot, but that may not be a big deal for them, while some patients who are social or have to give a speech frequently, coughing may be a huge issue. In addition to physical discomfort, a protracted cough could also cause anxiety, social and personal embarrassment, and deterioration in quality of life especially in psychosocial condition [
19,
20], which was also reflected in the last two items of CET with “Have your cough interfered with your daily life?”, and “Have your cough made you feel anxious or depressive?” . The CET correlated well with cough VAS and LCQ-MC, suggesting its great capability of assessing cough severity and cough-specific quality of-life. However, for chronic cough patients, especially for those who were diagnosed as unexplained or refractory chronic cough whose pathogenesis is inadequately understood and effective treatment is still lacking, whether CET is appropriated tool for long-term management and which cutoff score of CET is appropriate to identify the need of drug therapy still require further research.
Koo, Hyeon-Kyoung et al. have described the validation of another cough assessment test (COAT) [
21]. Unlike the full evaluation of CET on cough severity, social impact and psychological effect, the COAT focuses on cough frequency, limitation on daily activities, sleep disturbance, fatigue and hypersensitivity to irritants, no sight of cough intensity and psychological impact. Further work is necessary to compare the CET and COAT in the evaluation of chronic cough.
There are limitations to our study. The MID of CET was just based on distribution-based method. Several studies have showed that a MID based on anchor-based approach was close to the value of one SEM [
22,
23], while a few discrepancies were showed in other researches [
24,
25]. It seems that one SEM equals the MID is not a universal truth [
26]. In addition, the subjects selected for the test validation were older than 14 years without overt identifiable abnormalities on chest X-ray, which may restrict its application in children and those with abnormal chest radiograph.
Conclusion
We develop a new cough evaluation test consisting 5 items. Through assessment with concurrent validation, internal consistency, repeatability, responsiveness and the minimal important difference, CET is a reliable, valid and responsive tool to simply evaluate full impact of chronic cough in regard of physical, social and psychological aspects. CET would facilitate an easy and efficient way to assess chronic cough in routine care and clinical trials.
Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit
http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (
http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.