Validation of the Summit Lab Score in Predicting Exacerbations of Chronic Obstructive Pulmonary Disease Among Individuals with High Arterial Stiffness

Figures & data

Table 1 Baseline Characteristics of the Study Population (N = 430), Overall and Stratified by Textiles of the Summit Lab Score

Characteristics	Overall (N = 430)	Summit Lab Score			P value
		Tertile 1 (n = 142)	Tertile 2 (n = 134)	Tertile 3 (n = 154)
Demographics
Age, years^a	68.5 ± 7.9	65.6 ± 7.9	69.6 ± 7.6	70.2 ± 7.5	< 0.001
Male, n (%)	341 (79)	100 (70)	109 (81)	132 (86)	0.004
Race/ethnicity
African American	17 (4)	6 (4)	4 (3)	7 (5)	0.064
Asian	206 (48)	53 (37)	74 (55)	79 (51)
White	205 (48)	83 (58)	55 (41)	67 (44)
Others/mixed race	2 (< 1)	0	1 (< 1)	1 (< 1)
Smoking history, n (%)
Current	160 (37)	48 (34)	50 (37)	62 (40)	0.517
Ex-smoker	270 (63)	94 (66)	84 (63)	92 (60)
Smoking history, pack years^a	49.7 ± 28.7	43.1 ± 26.4	50.7 ± 28.5	54.9 ± 30.0	0.002
Physical examination
Weight, kg	69.4 ± 18.1	75.2 ± 16.6	67.5 ± 17.7	65.7 ± 18.6	< 0.001
Height, cm	167.2 ± 9.4	168.2 ± 9.3	166.3 ± 9.6	167.0 ± 9.3	0.230
BMI,^a kg/m^2	24.6 ± 5.1	26.4 ± 4.9	24.2 ± 4.9	23.3 ± 5.1	< 0.001
Systolic blood pressure^a, mmHg	134.2 ± 15.1	132.4 ± 13.6	136.1 ± 15.9	134.4 ± 15.7	0.131
Diastolic blood pressure, mmHg	79.5 ± 9.7	79.6 ± 8.6	79.2 ± 10.7	79.8 ± 9.6	0.864
Heart rate^a (beats per minute)	77.4 ± 12.2	73.4 ± 10.2	77.4 ± 11.3	81.1 ± 13.6	< 0.001
Previous moderate/severe COPD exacerbation in the prior 3 years
Treated,^b not hospitalized	0.73 ± 1.17	0.61 ± 1.07	0.69 ± 1.20	0.88 ± 1.21	0.132
Hospitalized^a	0.21 ± 0.59	0.12 ± 0.42	0.18 ± 0.53	0.31 ± 0.74	0.015
Treated^b and hospitalized	0.94 ± 1.44	0.73 ± 1.15	0.87 ± 1.44	1.19 ± 1.64	0.020
Risk factors and medical history^c
History of hypertension^c	278 (65)	93 (65)	94 (70)	91 (59)	0.142
History of hyperlipidemia^c	178 (41)	77 (54)	44 (33)	57 (37)	< 0.001
Diabetes mellitus diagnosis^a,c	81 (19)	27 (19)	30 (22)	24 (16)	0.337
Prior myocardial infarction^a,c	27 (6)	8 (6)	5 (4)	14 (9)	0.161
Prior heart failure diagnosis^a,c	7 (2)	1 (<1)	2 (1)	4 (3)	0.433
Prior cerebrovascular accident^c	17 (4)	6 (4)	4 (3)	7 (5)	0.779
Prior CAD diagnosis^c	55 (13)	13 (9)	16 (12)	26 (17)	0.130
Prior pneumonia diagnosis^c	70 (16)	24 (17)	18 (13)	28 (18)	0.536
Spirometric measurements
FEV1, mL^a	1165 ± 446	1280 ± 486	1202 ± 461	1026 ± 348	< 0.001
FVC, mL	2465 ± 753	2593 ± 810	2482 ± 772	2331 ± 656	0.011
FEV1/FVC ratio	0.48 ± 0.12	0.50 ± 0.11	0.49 ± 0.11	0.45 ± 0.12	< 0.001
Medications at baseline
Lipid lowering agents	115 (27)	50 (35)	26 (19)	39 (25)	0.011
Antithrombotic agents^a	113 (26)	42 (30)	31 (23)	40 (26)	0.48
Beta-blockers	57 (13)	22 (15)	18 (13)	17 (11)	0.53
Diuretics	73 (17)	26 (18)	24 (18)	23 (15)	0.70
Calcium channel blockers	116 (27)	36 (25)	44 (33)	36 (23)	0.17
Anti-arrhythmics^a	3 (< 1)	1 (< 1)	1 (< 1)	1 (< 1)	0.995
RAAS inhibitors	149 (35)	56 (39)	45 (34)	48 (31)	0.31
Anti-hypertensives	30 (7)	9 (6)	14 (10)	7 (5)	0.14
Xanthines^a	1 (< 1)	0	1 (< 1)	0	0.33
Short-acting anticholinergics	26 (6)	8 (6)	7 (5)	11 (7)	0.77
Mucolytics	22 (5)	7 (5)	7 (5)	8 (5)	0.99
Supplemental oxygen	12 (3)	2 (1)	4 (3)	6 (4)	0.42
Corticosteroids (inhaled)	1 (< 1)	0	0	1 (< 1)	0.41
Long-acting beta-2 agonists	2 (< 1)	0	0	2 (< 1)	0.17
Long-acting anticholinergics	1 (< 1)	0	0	1 (< 1)	0.41
Laboratory parameters
Hematocrit, %	43.8 ± 4.4	43.6 ± 3.5	43.3 ± 4.5	44.3 ± 4.9	0.13
White blood cell count, 10^9/L	7.39 ± 2.09	7.64 ± 2.24	7.05 ± 1.86	7.44 ± 2.13	0.06
Platelet count, 10^9/L	231.7 ± 65.1	223.0 ± 52.5	241.3 ± 79.3	231.4 ± 61.0	0.07
Mean corpuscular volume^a, fL	95.4 ± 5.6	93.5 ± 3.8	94.7 ± 6.2	97.7 ± 5.7	< 0.001
MCHC, g/dL	32.7 ± 1.0	33.0 ± 0.9	32.8 ± 1.0	32.4 ± 1.0	< 0.001
Red cell distribution width,^a %	15.1 ± 1.5	14.5 ± 0.9	15.0 ± 1.5	15.7 ± 1.8	< 0.001
Mean platelet volume, fL	8.98 ± 1.20	9.24 ± 1.21	8.82 ± 1.22	8.88 ± 1.15	0.007
Sodium, mmol/L	140.3 ± 3.1	140.5 ± 2.6	139.8 ± 3.3	140.5 ± 3.3	0.10
Potassium, mmol/L	4.39 ± 0.49	4.37 ± 0.45	4.38 ± 0.54	4.42 ± 0.48	0.58
Bicarbonate, mmol/L	23.3 ± 2.8	22.8 ± 2.6	23.4 ± 2.64	23.8 ± 2.96	0.006
Calcium, mg/dL	9.38 ± 0.45	9.39 ± 0.44	9.34 ± 0.42	9.40 ± 0.49	0.48
Glucose, mg/dL	107.6 ± 33.7	106.5 ± 29.5	110.9 ± 38.9	105.7 ± 32.4	0.37
Creatinine, mg/dL	0.96 ± 0.37	0.91 ± 0.36	0.96 ± 0.35	1.02 ± 0.39	0.0497
C-reactive protein, mg/L	2.8 (1.3, 6.3)	2.8 (1.4, 5.7)	2.9 (1.3, 7.5)	2.6 (1.2, 6.3)	0.34

Notes: Data are expressed as mean ± standard deviation or number (%), with one exception: C-reactive protein is expressed as median (interquartile range). ^aComponent variable of the Summit Lab Score. ^bTreated with oral or systemic corticosteroids with or without antibiotics. ^cThe statistical comparison across risk score tertiles includes both patients with and without the risk factor or medical history for this characteristic.

Abbreviations: BMI, body mass index; CAD, coronary artery disease; COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; MCHC, mean corpuscular hemoglobin concentration; RAAS, renin angiotensin aldosterone system.

Figure 1 Kaplan–Meier survival curves for moderate-to-severe AECOPD by Summit Lab Score tertile.

Abbreviation: AECOPD, acute exacerbation of chronic obstructive pulmonary disease.

Figure 2 Kaplan–Meier survival curves for CV event by Summit Lab Score tertile. CV event includes any of the following: myocardial infarction, unstable angina, stroke, transient ischemic attack, or CV mortality.

Abbreviation: CV, cardiovascular.

Table 2 Analysis of Spirometry Measures by Summit Lab Score Tertile

Spirometry Measure	Timepoint	Overall^a	Summit Lab Score			P value^f
			Tertile 1^b	Tertile 2^c	Tertile 3^d,e
FEV1 (mL)	12 weeks	1243 ± 480	1379 ± 517	1282 ± 483	1051 ± 362	< 0.001
	24 weeks	1217 ± 481	1337 ± 525	1251 ± 488	1042 ± 359	< 0.001
FEV1 change from baseline (mL)	12 weeks	63.5 ± 216.5	92.5 ± 240.2	76.1 ± 218.6	17.9 ± 177.4	0.007
	24 weeks	41.2 ± 228.8	54.7 ± 289.2	60.1 ± 192.2	4.1 ± 181.6	0.105
FVC (mL)	12 weeks	2570 ± 799	2713 ± 878	2622 ± 794	2357 ± 665	< 0.001
	24 weeks	2512 ± 798	2660 ± 863	2537 ± 793	2315 ± 685	0.001
FVC change from baseline (mL)	12 weeks	93.0 ± 384.0	119.9 ± 378.6	119.6 ± 427.3	35.1 ± 335.6	0.087
	24 weeks	52.5 ± 400.7	81.5 ± 456.4	63.0 ± 349.8	7.1 ± 386.1	0.173
FEV1/FVC ratio	12 weeks	0.49 ± 0.12	0.51 ± 0.12	0.50 ± 0.13	0.45 ± 0.11	< 0.001
	24 weeks	0.49 ± 0.13	0.51 ± 0.12	0.50 ± 0.16	0.45 ± 0.10	0.006
FEV1/FVC change from baseline	12 weeks	0.01 ± 0.06	0.01 ± 0.06	0.01 ± 0.06	0.00 ± 0.07	0.064
	24 weeks	0.01 ± 0.08	0.00 ± 0.05	0.02 ± 0.11	0.00 ± 0.08	0.503

Notes: ^an = 429 at baseline; 362 at 12 weeks, and 333 at 24 weeks. ^bn = 142 at baseline; 127 at 12 weeks, and 116 at 24 weeks. ^cn = 134 at baseline; 120 at 12 weeks, and 115 at 24 weeks. ^dFor absolute values: n = 153 at baseline; 115 at 12 weeks, and 102 at 24 weeks. ^eFor values of change from baseline: n = 153 at baseline; 114 at 12 weeks, and 101 at 24 weeks. ^fP-values are from a test of linear contrasts.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity.

Figure 3 Length of stay (y-axis) in the hospital, hospital ward, or intensive care by Summit Lab Score tertile. P values are from tests of linear contrasts with coefficients of –1, 0 and 1. Error bars are the mean ± standard deviation, with the relevant mean and standard deviation provided on the graph near each tertile’s line.