CAT score as a prognostic tool in low resource setting: Exploring the correlation between CAT score, exacerbation history with BODE Index in stable COPD

Abstract

Background:

Chronic obstructive pulmonary disease (COPD) is a significant global health concern, projected to be the fourth leading cause of death by 2030. This study explores the correlation between the COPD assessment test (CAT) score, history of exacerbations, and the BODE Index in stable COPD patients. While the BODE Index is a validated multidimensional grading system, its application in outpatient settings, especially in resource-constrained setting, can be challenging due to the need for spirometry.

Methods:

We conducted a cross sectional, observational study. It was conducted over 18 months in Mumbai and recruited 50 stable COPD patients. The CAT score and history of exacerbations in the previous year were evaluated alongside the BODE Index and other demographic data.

Statistical:

The correlation between quantitative variables was performed using Pearson and Spearman’s correlation coefficient, with P < 0.05 considered statistically significant.

Results:

In the study population, the mean rate of exacerbation observed was 1.52 (SD = 2.279)/person/year, and the mean CAT score was 9.88 ± 7.34 (range: 0–27). The median BODE Index was 3 with most of the patients 44% (n = 22) having a BODE score falling in the first quartile. Positive correlations r (Pearson’s) =0.468 (P = 0.000614) and σ (Spearman’s) =0.2797 (P = 0.0490) were observed between CAT score with BODE Index and exacerbation history and BODE Index, respectively, indicating a moderate positive correlation between CAT score and BODE Index and statistically significant, albeit weak, correlation with exacerbation history.

Conclusions:

Our findings suggest that simple tools like CAT and exacerbation history can be used as surrogates for the BODE Index.

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is a common chronic disease, causing significant morbidity and mortality, worldwide. By the year 2030, it is projected to be the cause of 7.8% of total deaths worldwide, becoming the fourth leading cause of death.[1] Mirroring global trends, COPD is projected to be the third leading cause of death and the fifth leading cause of loss of Disability Adjusted Life Years in India by 2030.[1]

COPD, though historically defined by the spirometric parameter of obstruction, is now considered to be a complex disease, characterized by systemic inflammation with various comorbidities and systemic consequences.[2] The recognition of the systemic effects of COPD led to the development of a multidimensional grading system, the BODE index, for the categorization and prediction of mortality outcomes in COPD patients.[3]

Though a well-validated tool, the use of the BODE index can potentially be limited in outpatient clinical settings, particularly in low and middle-income countries such as India owing to the requirement of spirometry for measuring airway obstruction and enough resources to perform a six-minute walk test (6MWT). Another concern is the inapplicability of the BODE index in patients who are too sick or otherwise immobilized to perform spirometry and the 6MWT. Likewise, other prognostic indices such as the age dyspnoea obstruction index, useful in severe and longstanding COPD, also require spirometry.[4]

Acute exacerbation is a known risk factor for reduction in lung function[5] and poor overall health status in COPD patients.[6] It is also associated with higher mortality rates.[7,8,9] The COPD assessment test (CAT) score is a short, simple questionnaire for assessing and monitoring COPD. It provides a valid, reliable, and standardized measure of COPD health status.[10] The predictive power of CAT for all-cause mortality in COPD patients has also been exhibited.[11]

The current management guidelines for stable COPD by the global initiative for chronic obstructive lung disease recommend the use of the CAT score and history of exacerbations in the previous year, to categorize patients and to decide their pharmacological management.

In this study, we have examined the correlation of CAT score and history of exacerbations with the BODE index in stable COPD patients – as an easier means to predict the outcome of the disease.

SUBJECTS AND METHODS

The study was conducted in the Outpatient Department of the Department of Respiratory Medicine, in a tertiary care centre in Mumbai. The study was carried out over a period of 18 months. Fifty subjects meeting the inclusion criteria were selected from amongst the patients attending the outpatient clinic.

Patients with stable COPD were considered eligible for inclusion in the study, where the stable was defined as patient’s stable condition continuing for ≥3 months with normal day-to-day variations and without any signs of airway infection,[12] and COPD was defined as postbronchodilator forced expiratory volume in the first second (FEV1)/forced vital capacity (FVC) ratio of <0.7. Patients with a diagnosis of bronchial asthma, active pulmonary tuberculosis, and decompensated heart disease were excluded from the study.

The study was initiated after approval from the Institutional Ethics Committee. A written informed consent was obtained from all study subjects before enrolling them in the study.

Patient data was collected using a structured case record form, developed for the study. This included relevant demographic data, illness course, risk factors, history of exacerbations in the previous year, symptoms, physical examination findings, and relevant investigations. Airflow limitation was measured with spirometry, measuring FEV1, FVC, and FEV1/FVC ratio. Both pre-bronchodilator and post-bronchodilator (15 min after administration of 200–400 µg of salbutamol) values were obtained. The CAT respiratory questionnaire was administered to all the subjects in their own language. Patients were explained how to fill out the questionnaire and assisted in its completion. The 6MWT was performed according to American Thoracic Society guidelines. The total 6-minute walk distance (6MWD) and nadir oxygen saturation during the test as well as vitals before and after the test were recorded. The BODE index for each patient was calculated for each patient, combining body mass index (BMI), FEV1 (percentage predicted), and dyspnoea as assessed by modified Medical Research Council (mMRC) grading and the 6MWD.

Statistical analysis

Descriptive analyses were conducted by calculating mean and standard deviation (SD) for continuous variables and frequency and percentages for discrete variables. The correlation between quantitative variables was performed using Pearson and Spearman’s correlation coefficient, with P < 0.05 considered statistically significant.

RESULTS

Table 1 summarizes the sociodemographic and clinical profile of the study subjects. Among the study subjects, 64% (n = 32) had either no or only one exacerbation in the previous year, whereas 20% (n = 10) had two or three exacerbations, and 16% (n = 8) had more than three exacerbations in the previous year. The mean rate of exacerbation observed in the study population is 1.52 (SD = 2.279) per person per year. It was also observed that 14.47% of the exacerbations were severe enough to warrant hospital admission.

Table 1.

Characteristics of patients’ sample

Variable		Mean		Standard deviation
Age (years)		61.98		10.40
Duration of COPD (years)		6.91		8.54
FEV1 (%)		51.42		13.79
BMI (kg/m2)		22.11		3.78
6MWD (m)		297.90		64.82
Smoking index		685.87		633.09
Variable		Percentage		Number (n)
Gender
Male		96		48
Female		4		2
Symptoms
No symptom		14		7
Breathlessness		78		39
Cough		50		25
Sputum production		34		17
Wheezing		12		6
Comorbidities
Chest pain		8		4
No comorbidity		50		25
Hypertension		28		14
Post-tuberculosis sequalae		16		8
Ischaemic heart disease		12		6
Diabetes mellitus		10		5
Environmental risk factor
None		0		0
Indoor air pollution		82		41
Smoking		60		30
Outdoor air pollution		14		7
GOLD stage
I		2		1
II		54		27
III		42		21
IV		2		1

GOLD=Global initiative for chronic obstructive lung disease, BMI=Body mass index, 6MWD=6-minute walk distance, COPD=Chronic obstructive pulmonary disease, FEV1=Forced expiratory volume in first second

The mean CAT score was 9.88 ± 7.34 (range 0–27). The most frequently reported domain in the CAT score was exertional breathlessness and the least reported one pertained to sleep disturbances. CAT impact level categorization was done based on the CAT scores for all study subjects.[13] A total of 60% of subjects (n = 30) had LOW–CAT impact (CAT score 0–10), 28% (n = 14) had MEDIUM–CAT impact (CAT score 11–20), and 12% (n = 6) had high-CAT impact (CAT score 21–30). None had scores more than 30 meeting the criteria for very high-CAT impact.

BODE Index was calculated for all subjects based on BMI, airway obstruction (indicated by FEV1-percentage predicted), dyspnoea level (indicated by mMRC grading), and exercise tolerance (indicated by 6MWD distance). The median BODE Index of the study sample was 3 with most of the patients 44% (n = 22) having a BODE score falling in the first quartile, 30% (n = 15) in the second quartile, 20% (n = 10), and 6% (n = 3) in the third and fourth quartiles, respectively.

The correlation between the CAT score and BODE Index was calculated using Pearson’s Correlation coefficient (r) [Figure 1]. A positive correlation of r = 0.468 (P = 0.000614) was observed between the CAT Score and the BODE Index. The correlation between the CAT Impact Score and BODE Index was calculated using Spearman’s rank correlation coefficient (ρ). A positive correlation of ρ =0.3803 (P = 0.0064) was noted.

Figure 1.

Correlation of chronic obstructive pulmonary disease assessment test score and BODE Index

The correlation between exacerbation in the previous year and the BODE Index was calculated using the Spearman’s rank correlation (ρ) coefficient, and it was found to be 0.2797 (P = 0.0490).

DISCUSSION

Our study aimed to identify the correlation of CAT score and exacerbation pattern in the previous year with BODE Index in stable COPD patients. Both of these factors have already been recognized as important for the overall assessment and management of stable COPD patients by the global initiative for chronic obstructive lung disease.[14] As such, these are routinely assessed and used in daily clinical practise as well. We propose that the demonstration of a strong positive correlation between each of these factors and the BODE Index would make the case for the adoption of CAT score and exacerbations as prognostic markers in stable COPD patients. This would be particularly useful in outpatient clinics in low and middle-income (LAMI) countries such as India, where large patient volumes make complex measures such as the BODE Index impractical for daily use.

We observed a positive correlation between the CAT Score and the BODE Index with r = 0.468, r² = 0.022 (P < 0.05). The CAT Impact Scores were correlated with the BODE Index (Spearman’s rank correlation) with r = 0.38 (P < 0.05). A study by Ladeira et al. established a positive correlation between the CAT score and BODE Index of r = 0.475 (P < 0.01) and between the CAT Impact Score and BODE Index of r = 0.377 (P = 0.004).[15] Similarly, Singh et al. demonstrated a positive correlation between CAT scores and the BODE Index of r = 0.8038 (P < 0.001).[16] We postulate that the comparatively weaker correlation that we observed may be attributed to differences in our study sample. The mean duration of illness (COPD) of our study sample was relatively lesser at 6.91 ± 8.54 years. Also, the mean CAT score in our sample (mean = 9.88, SD = 7.34) was smaller as compared to a mean CAT score of 19.61 (SD = 8.07) observed by Singh et al. Interestingly, Ladeira et al., who had a sample mean CAT score of 10.7, SD = 7.4, observed a positive correlation of r = 0.475 (P < 0.01), similar to ours.

We observed a mean rate of 1.52 exacerbations per person per year. 64% of our study subjects reported less than two exacerbations in a year. Sadatsafavi et al. reported 1.53 exacerbations per patient annually[17] similar to our study. Most studies report an annual rate of between 0.5 and 3.5 exacerbations per year.[18] We also observed a weak positive correlation between exacerbations in the previous year and the BODE Index (Spearman’s Rank correlation) with r = 0.279, P = 0.049. A similar weak positive correlation was observed by Hodgev et al. with r = 0.36; P = 0.002.[19]

Limitations

Our study sample had a skewed sex distribution with 96% of subjects being males. Most of our study subjects had a relatively shorter duration of illness and had comparatively smaller CAT scores. We acknowledge that this may hinder generalisability to a sicker patient population.

CONCLUSIONS

We were able to establish a moderate positive correlation between the CAT Score and the BODE Index and a statistically significant albeit weak positive correlation between exacerbations and the BODE Index. Our findings are in agreement with previous research in this field and highlight that a simple, easy-to-administer questionnaire like CAT can have significant value in daily clinical practice in resource-constrained outpatient settings in LAMI countries such as India.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.