The repeatability of interleukin-6, tumor necrosis factor-α, and C-reactive protein in COPD patients over one year

Figures & data

Table 1 Baseline characteristics of the study patients

Characteristic	n = 58 COPD
Age (years)	63.78 (8.32)
Gender, male/female	40/18
Current/Ex-smokers	23/35
Pack year history^a	42.5 (36–53.5)
Inhaled steroids use/no use	31
Long acting beta agonist use	27
Long acting anticholinergic use	10
Methylxanthines use	5
Pre-bronchodilator FEV1 % predicted	56.71 (13.11)
Pre-bronchodilator FVC % predicted	93.64 (17.77)
Post-bronchodilator FEV1% predicted	64.09 (14.16)
Post bronchodilator FEV1 (L)	1.79 (0.6)
Post bronchodilator FEV1/FVC ratio (%)	51.39 (10.05)

Abbreviations: COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in one second; FVC, forced vital capacity; IQR, interquartile range; SD, standard deviation.

Notes: Lung function measurements were standardized for age and gender. There were no patients on oral corticosteroids. Results presented as mean (SD) or median (IQR).

Table 2 Pulmonary function at the baseline visit and one-year visit

Pulmonary function	Baseline	Year 1
Pre-bronchodilator FEV1 % predicted	56.71 (13.1)	57.49 (13.2)
Post-bronchodilator FEV % predicted	64.09 (14.2)	63.63 (14.9)
Raw^a (kPa.sec)	0.46 (0.4–0.5)	0.47 (0.4–0.5)
sGaw^a (kPa.sec)	0.46 (0.4–0.5)	0.47 (0.4–0.5)
FRC (% predicted)	132.02 (29.0)	128.17 (30.5)
IC (L)	2.33 (0.6)	2.40 (0.6)
TLC % predicted	106.44 (16.2)	103.11 (15.2)
RV % predicted	147.27 (35.8)	131.16 (41.3)
KCO % predicted	89.49 (25.1)	89.08 (24.8)

Abbreviations: CI, confidence interval; FEV₁, forced expiratory volume in one second; FRC, functional residual capacity; IC, inspiratory capacity; KCO, carbon monoxide diffusion factor; Raw, airways resistance; RV, residual volume; SD, standard deviation; sGaw, specific airways conductance; TLC, total lung capacity.

Notes: Lung function measurements were standardized for age and gender. There were no patients on oral corticosteroids. Results presented as mean (SD) or geometric mean (95% CI).

Figure 1 FEV₁ % predicted for each patients at the baseline and year 1 visit.

Table 3 Repeatability of systemic measurements over the one year interval

Systemic indices	Baseline	Year 1	p value	Ri and p value
IL-6 (pg/ml)	3.2 (2.5–4.1)	3.1 (2.6–3.7)	0.75	0.50 0.001
CRP (pg/ml)	3.3 (2.5–4.4)	2.9 (2.3–3.6)	0.57	0.57 <0.0001
TNF-α (pg/ml)	1.8 (1.6–2.0)	1.6 (1.4–1.9)	0.41	0.57 <0.0001

Abbreviations: CRP, C-reactive protein; IL-6, interleukin-6; TNF-α, tumor necrosis factor-α.

Note: Data presented as geometric mean (95% CI).

Figure 2 Bland–Altman plots for a) IL-6, b) CRP and c)TNFα collected with a one year interval. The dotted lines represent the mean difference ± 2 SD.

Abbreviations: CRP, C-reactive protein; IL, interleukin; TNFα, tumor necrosis factor-α.

Table 4a Relationships between systemic inflammatory biomarkers and BMI at the baseline visit

	CRP	TNF-α	BMI
IL-6	r = 0.55, p = 0.0001	r = 0.11, p = 0.47	r = −0.10, p = 0.49
CRP		r = 0.18, p = 0.20	r = 0.18, p = 0.22
TNF-α			r = −0.11, p = 0.44

Abbreviations: BMI, body mass index; CRP, C-reactive protein; IL-6, interleukin-6; TNF-α, tumor necrosis factor-α.

Table 4b Relationships between systemic inflammatory biomarkers and BMI at the one-year visit

	CRP	TNF-α	BMI
IL-6	r = 0.51, p = 0.0002	r = 0.18, p = 0.23	r = 0.25, p = 0.09
CRP		r = −0.11, p = 0.41	r = 0.26, p = 0.06
TNF-α			r = −0.20, p = 0.16

Abbreviations: BMI, body mass index; CRP, C-reactive protein; IL-6, interleukin-6; TNF-α, tumor necrosis factor-α.

Figure 3a The relationship between CRP and IL-6 at the baseline visit.

Abbreviations: CRP, C-reactive protein; IL-6, interleukin-6.

Figure 3b The relationship between CRP and IL-6 at the one-year visit.

Abbreviations: CRP, C-reactive protein; IL-6, interleukin-6.