Components of the COPD Assessment Test (CAT) associated with a diagnosis of COPD in a random population sample

Figures & data

Table 1.  Subject characteristics

Variable	All n = 532	COPD n = 51	Non-COPD n = 481	p-value *
Age, yrs	60.1 (11.4)	63.0 (9.5)	59.7 (11.6)	0.05
Male, n (%)	248 (47)	23 (45)	225 (47)	0.82
Body mass index, kg/m2	28.3 (5.9)	28.4 (5.5)	28.3 (6.0)	0.90
Smoking status, n (%):				<0.0001
Never	250 (47)	10 (20)	240 (50)
Former	214 (40)	24 (47)	190 (40)
Current	68 (13)	17 (33)	51 (11)
Smoking history, pack-yrs	13 (21)	33 (21)	11 (19)	<0.0001
Post-bronchodilator spirometry:
FEV1, L	2.87 (0.78)	2.23 (0.74)	2.94 (0.76)	<0.0001
FEV1,% predicted	98 (17)	79 (19)	100 (16)	<0.0001
FVC, L	3.83 (1.02)	3.65 (1.07)	3.85 (1.01)	0.19
FEV1/FVC,%	75 (8)	60 (8)	77 (7)	<0.0001
Bronchodilator responsiveness:
ΔFEV1, L	0.09 (0.16)	0.09 (0.17)	0.09 (0.15)	0.91
ΔFEV1,%	3.6 (6.6)	4.8 (9.0)	3.5 (6.3)	0.16
GOLD stage, n (%):
I	49 (9.2)	27 (52.9)	22 (4.6)
II	21 (3.9)	20 (39.2)	1 (0.02)
III	3 (0.6)	3 (5.9)	0
IV	1 (0.2)	1 (2.0)	0
MRC dyspnea scale (0–4)	0.4 (0.7)	0.6 (0.8)	0.3 (0.7)	0.01
CAT score:
Total	7.1 (6.2)	9.2 (6.6)	6.9 (6.2)	0.01
Cough	1.3 (1.1)	1.7 (1.2)	1.3 (1.1)	0.01
Phlegm	0.9 (1.1)	1.4 (1.1)	0.8 (1.1)	0.001
Chest tightness	0.6 (1.0)	0.8 (1.1)	0.6 (1.0)	0.09
Breathlessness	1.1 (1.3)	1.8 (1.7)	1.0 (1.3)	0.003
Activity limitation	0.4 (1.2)	1.0 (1.5)	0.6 (1.1)	0.08
Confident to leave home	0.2 (0.8)	0.3 (0.9)	0.2 (0.8)	0.57
Sleep	0.9 (1.2)	0.7 (1.1)	0.9 (1.2)	0.31
Energy	1.4 (1.2)	1.5 (1.3)	1.4 (1.2)	0.62

Values are means (SD) unless otherwise specified.

* p-value is based on the significance test (t-test, ANOVA or Chi-square) used to compare COPD and non-COPD subjects.

Δ = pre- to post-bronchodilator change.

Figure 1.  ROC curve for the final model which included age, smoking status and the CAT breathlessness score. The area under the curve for the model is 0.772.

Table 2.  Odds ratio estimates for components of the final model that related to COPD

Effect	Point Estimate	95% Wald Confidence Limits
Ages ≥55 years	4.39	1.91	10.10
Smoking: current vs. never	8.46	3.31	21.58
Smoking: former vs. never	2.81	1.25	6.30
CAT breathlessness	1.28	1.05	1.58

Figure 2.  Decision tree based on the final logistic regression model. Where the outcome of the model had a low probability of COPD, we recommend no further screening. Where the model determines an increased probability of COPD, we recommend going on to confirmatory testing with spirometry.

Table 3.  Diagnosis of COPD based on components of the final model and a logistic probability of 0.097

Observation	Smoking	Breathlessness	Age	p value	Screen
1	0	0	0	0.00977	No
2	0	0	1	0.04150	No
3	0	1	0	0.01250	No
4	0	1	1	0.05263	No
5	0	2	0	0.01598	No
6	0	2	1	0.06653	No
7	0	3	0	0.02040	No
8	0	3	1	0.08378	No
9	0	4	0	0.02603	No
10	0	4	1	0.10501	Yes
11	0	5	0	0.03315	No
12	0	5	1	0.13083	Yes
13	1	0	0	0.02694	No
14	1	0	1	0.10838	Yes
15	1	1	0	0.03430	No
16	1	1	1	0.13491	Yes
17	1	2	0	0.04359	No
18	1	2	1	0.16673	Yes
19	1	3	0	0.05524	No
20	1	3	1	0.20427	Yes
21	1	4	0	0.06978	No
22	1	4	1	0.24776	Yes
23	1	5	0	0.08780	No
24	1	5	1	0.29705	Yes
25	2	0	0	0.07697	No
26	2	0	1	0.26800	Yes
27	2	1	0	0.09665	Yes
28	2	1	1	0.31960	Yes
29	2	2	0	0.12070	Yes
30	2	2	1	0.37604	Yes
31	2	3	0	0.14975	Yes
32	2	3	1	0.43605	Yes
33	2	4	0	0.18431	Yes
34	2	4	1	0.49800	Yes
35	2	5	0	0.22475	Yes
36	2	5	1	0.56001	Yes

Smoking status categories: 0 = non-smoker, 1 = former smoker, 2 = current smoker.

Breathlessness is from the CAT item score, 0-5.

Age categories: 0 = <55, 1 = ≥55 years.

The predictive probabilities (p) are calculated from the fitted logistic regression model for the COPD outcome with age category, smoking status, and CAT breathless score as independent variables.

Screen: Using a cutpoint determined from the ROC curve (0.097), any probability below the cutpoint is negative and any above is positive for screening.