The YKL-40 protein is a potential biomarker for COPD: a meta-analysis and systematic review

Figures & data

Figure 1 The flow diagram of included and excluded studies.

Table 1 Characteristics of studies involving the association between serum/sputum YKL-10 and COPD

Author	Year	Size	Sex (M/F)		Samples	Age		Case			Control			Unit	Method	Score
		Case/control	Case	Control		Case	Control	Mean	SD	N	Mean	SD	N
Cai^Citation19	2013	125/20	68/57	13/7	Serum	59.50±9.06	56.7±8.21	52.59	17.05	125	26.38	3.29	20	ng/mL	ELISA	7
Gu et al^Citation20	2015	80/80	47/33	44/46	Serum	64.85±7.62	65.12±7.73	78.34	10.62	80	65.63	8.98	80	ng/mL	ELISA	7
Gumus et al^Citation21	2013	52/26	48/4	23/3	Serum	60.2±10.1	57.8±9.9	199.4	108.8	52	171.1	80.0	26	ng/mL	ELISA	7
Han et al^Citation22	2016	16/20	16/0	0/20	Serum	70.33±32.51	49±13.56	353	239.71	16	190.5	162.18	20	ng/mL	ELISA	6
Holmgaard et al^Citation23	2013	493/3,130	247/246	1,293/1,837	Serum	70.69±7.46	NR	275.0	151.03	493	62.25	19.91	3,130	ng/mL	ELISA	6
James et al^Citation15	2016	45/48	NR	NR	Serum	NR	NR	81.2	80.26	45	22.2	7.18	48	ng/mL	ELISA	7
Kim et al^Citation24	2012	30/73	20/10	41/32	Serum	70±13	48±13	298.67	228.08	30	33.33	33.28	73	ng/mL	ELISA	6
Létuvé et al^Citation25	2008	30/15	23/7	8/7	Serum	NR	54.17±3.68	81.0	95.59	30	21.3	24.7	15	ng/mL	ELISA	6
Sakazaki et al^Citation26	2011	45/58	38/7	36/22	Serum	67.9±1.3	63.25±2.90	268.9	32.3	45	252.14	83.27	58	ng/mL	ELISA	7
Song et al^Citation27	2016	60/60	41/19	NR	Serum	NR	NR	168.1	26.65	60	58.5	24.83	60	ng/mL	ELISA	7
Wen et al^Citation28	2016	119/50	56/63	25/25	Serum	59.3±6.4	59.5±7.4	52.93	16.94	119	26.32	3.54	50	ng/mL	ELISA	7
Zeng et al^Citation29	2016	110/20	74/36	13/7	Serum	70.05±11.05	68.69±9.86	46.52	20.85	110	26.18	7.78	20	ng/mL	ELISA	7
Gao et al^Citation30	2016	24/28	9/15	18/10	Sputum	59.3±7.0	47.3±13.14	50.83	21.30	20	22.35	25.22	28	ng/mL	ELISA	6
Gao et al^Citation30	2016	35/62	34/1	44/18	Sputum	72.2±8.1	61.55±11.25	21.27	15.23	35	16.34	18.55	62	ng/mL	ELISA	6
Otsuka et al^Citation31	2012	45/7	45/0	6/1	Sputum	72±9	67±5	346	325	45	125	122	7	ng/mL	ELISA	7

Abbreviations: M, male; F, female; SD, standard deviation; N, sample size; ELISA, enzyme-linked immunosorbent assay; NR, not reported.

Figure 2 The results of association between serum YKL-40 levels and COPD.

Note: Weights are from random effects analysis.
Abbreviations: SMD, standardized mean difference; CI, confidence interval.

Figure 3 The result of sensitivity analysis on association between serum YKL-40 levels and COPD.

Abbreviation: CI, confidence interval.

Table 2 Characteristics of studies involving in comparison of the differences of serum YKL-40 levels in the exacerbation group and the stable group

Author	Year	Size	Sex (M/F)		Stable			Exacerbation
		Case/control	Case	Control	Mean (ng/mL)	SD	N	Mean (ng/mL)	SD	N
Cai^Citation19	2013	125/20	68/57	13/7	40.40	8.83	65	65.8	13.60	60
Lai et al^Citation32	2016	81/47	54/27	28/19	51.13	33.95	44	84.37	53.91	37
Wen et al^Citation28	2016	119/50	56/63	25/25	40.32	8.43	59	65.32	13.74	60
Zeng et al^Citation29	2016	110/20	74/36	13/7	36	16.64	50	55.29	20.02	60

Abbreviations: M, male; F, female; SD, standard deviation; N, sample size.

Figure 4 Comparison of the differences of serum YKL-40 levels in the exacerbation group and the stable group.

Note: Weights are from random effects analysis.
Abbreviations: SMD, standardized mean difference; CI, confidence interval.

Figure 5 Pooled correlation coefficients between serum YKL-40 levels and FEV₁/predict%.

Note: Weights are from random effects analysis.
Abbreviation: CI, confidence interval.

Figure 6 The results of association between sputum YKL-40 levels and COPD.

Note: Weights are from random effects analysis.
Abbreviations: SMD, standardized mean difference; CI, confidence interval.

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