Influences of Two FEV₁ Reference Equations (GLI-2012 and GIRH-2017) on Airflow Limitation Classification Among COPD Patients

Figures & data

Figure 1 Subjects included for analysis.

Abbreviations: COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in one second; FVC, forced vital capacity; GLI, Global Lung Function Initiative; GIRH, Guangzhou Institute of Respiratory Health; LLN, Lower Limit of Normal.

Table 1 Consistency of AFL and COPD-SQ Score Groups and Clinical Characteristics of Each Group

COPD-SQ Score Group	FEV1/FVC<0.7		FEV1/FVC≥0.7		P value*
	N=743		N=2460
	≥16	<16	≥16	<16
N(%)	438 (59.0)	305 (41.0)	221 (9.0)	2239 (91.0)
COPD-SQ scores(SD)^#	18.78 (2.5)	10.69 (3.3)	17.98 (2.2)	8.74 (3.6)	<0.001
Age-year(SD)	67.45 (6.98)	58.5 (8.0)	69.15 (8.4)	54.91 (9.7)	<0.001
Male-N(%)^§	411 (93.6)	264 (86.5)	140 (63.3)	1211 (54.1)	<0.001
BMI scores(SD)	4.45 (1.8)	2.76 (1.7)	4.58 (1.9)	2.84 (1.7)	<0.001
Smocking index scores(SD)^£	1.79 (0.6)	1.41 (0.8)	0.87 (1.0)	0.59 (0.9)	<0.001
Cough scores(SD)	2.15 (1.4)	0.68 (1.3)	1.95 (1.4)	0.68 (1.3)	<0.001
Dyspnea scores(SD)	1.58 (1.2)	0.63 (1.0)	1.21 (1.0)	0.62 (0.9)	<0.001
Biofuel exposure scores(SD)	0.39 (0.5)	0.29 (0.5)	0.42 (0.5)	0.19 (0.4)	<0.001
Family history scores(SD)	0.64 (0.9)	0.38 (0.8)	0.73 (1.0)	0.25 (0.7)	<0.001

Notes: *P represents intra-group differences among the 4 groups; ^#The scores of each variable is expressed in the form of mean value and standard deviation, one-way ANOVA and Bonferroni method were used to analyze the differences of continuous variables in each group; ^§p value of the comparison between the normal group and the COPD group in subjects with COPD-SQ scores≥16 was <0.001; ^£p value of the comparison between the normal group and the COPD group in subjects with COPD-SQ scores≥16 was <0.001.

Abbreviations: AFL, airflow limitation; COPD-SQ, COPD screening questionnaire; BMI, body mass index; FEV1, forced expiratory volume in 1 s; FVC, forced vital capacity; SD, standard deviation.

Table 2 Severity Classification and Characteristics of Patients with GLI-2012 and GIRH-2017 FEV₁ Predicted Value Reference Equations

GOLD Grade	GLI-2012	GIRH-2017	P value^#
GOLD 1			P<0.001^$
N(%)	206 (34.5)	280 (46.9)	-
Sex (male, %)	167 (81.1)	229 (81.8)	0.336
Age (year, SD)	63.7 (8.6)	62.9 (8.5)	0.721
Smoking* (Yes, %)	148 (71.8)	201 (71.8)	0.564
GOLD 2
N(%)	244 (40.9)	202 (33.8)	-
Sex (male, %)	206 (84.4)	173 (85.6)	0.15
Age (year, SD)	64.6 (8.1)	65.2 (7.7)	0.683
Smoking* (Yes, %)	174 (71.3)	143 (70.8)	0.602
GOLD 3
N(%)	114 (19.1)	90 (15.1)	-
Sex (male, %)	109 (95.6)	87 (96.7)	0.44
Age (year, SD)	65.0 (8.1)	66.3 (8.4)	0.206
Smoking* (Yes, %)	85 (74.6)	68 (75.60)	0.888
GOLD 4
N(%)	33 (5.5)	25 (4.2)	-
Sex (male, %)	32 (97.0)	25 (100.0)	0.652
Age (year, SD)	62.9 (8.2)	63.8 (7.5)	0.674
Smoking* (Yes, %)	29 (87.9)	24 (96.0)	0.655
Total	597	597	-

Notes: ^#Data were collected from 597 patients who were diagnosed with COPD by GOLD 0.7 fixed ratio and both the GLI-2012 and GIRH-2017 LLN diagnosis thresholds. Differences in age were compared using t-test, and the chi-square test was used for comparison of categorical variables (percentage of patients in four severity stages, sex and smoking). ^$P value represents the difference of chi-square test in percentage of patients in four severity stages with the two reference formulas. *Smoking includes current smoking and ex-smoking.

Abbreviations: COPD, chronic obstructive pulmonary disease; SD, standard deviation; GOLD, Global initiative for chronic obstructive pulmonary disease; GLI, Global Lung Function Initiative; GIRH, Guangzhou Institute of Respiratory Health; LLN, lower limit of normal.

Table 3 Severity Distribution and Differences of 597 COPD Patients Classified by GIRH-2017 and GLI-2012 FEV₁ Predicted Value Reference Equations

FEV1 Reference Equation		GLI-2012^#(N)					GLI-2012(N)
		GOLD1	GOLD2	GOLD3	GOLD4		Yes	No	Total	P-value
GIRH-2017	GOLD1	201	79	0	0	Yes	201	79	280	<0.001
						No	5	312	317
						Total	206	391	597
	GOLD2	5	163	34	0	Yes	163	39	202	<0.001
						No	81	314	395
						Total	244	353	597
	GOLD3	0	2	80	8	Yes	80	10	90	0.001
						No	34	473	507
						Total	114	483	597
	GOLD4	0	0	0	25	Yes	25	0	25	0.039
						No	8	564	572
						Total	33	564	597

Notes: ^#Data were collected from 597 patients who were diagnosed with COPD by GOLD 0.7 fixed ratio and both the GLI-2012 and GIRH-2017 LLN diagnosis thresholds. McNemar method was performed for comparison analysis of the two FEV₁ reference equations, and the overall statistical difference between the two standards was P<0.001.

Abbreviations: COPD, chronic obstructive pulmonary disease; GOLD, global initiative for chronic obstructive pulmonary disease; GLI, Global Lung Function Initiative; GIRH, Guangzhou Institute of Respiratory Health; LLN, lower limit of normal.

Table 4 Correlations Between FEV₁%pred and CAT Scores, mMRC Grades, CCQ Scores, and Average AEs with GLI-2012 and GIRH-2017 FEV₁ Reference Equations

Variables	FEV1%pred
	GLI-2012	GIRH-2017
CAT scores
P	P<0.001	P<0.001
r^†(95% CI)	−0.386 (−0.462,-0.316)	−0.315 (−0.387,-0.242)
mMRC grades
P	P<0.001	P<0.001
r(95% CI)	−0.399 (−0.469,-0.322)	−0.342 (−0.418,-0.262)
CCQ scores
P	P<0.001	P<0.001
r(95% CI)	−0.296 (−0.373,-0.217)	−0.245 (−0.319,-0.166)
AE histories in the previous year
P	P<0.001	P<0.001
r(95% CI)	−0.227 (−0.305,-0.154)	−0.274 (−0.342,-0.206)

Notes: ^†r stands for correlation coefficient using Spearman correlation analysis. Data were collected from 597 patients who were diagnosed with COPD by GOLD 0.7 fixed ratio and both the GLI-2012 and GIRH-2017 LLN diagnosis thresholds.

Abbreviations: AEs, acute exacerbations; CAT, COPD assessment test; CCQ, COPD Clinical Questionnaire; COPD, chronic obstructive pulmonary disease; FEV₁%pred, FEV₁% predicted value; GOLD, Global initiative for chronic obstructive pulmonary disease; GLI, Global Lung Function Initiative; GIRH, Guangzhou Institute of Respiratory Health; LLN, Lower Limit of Normal; mMRC, the modified British Medical Research Council; 95% CI, 95% confidence interval.

Figure 2 Distribution of symptoms and exacerbation risk assessments of AFL severity under GIRH-2017 and GLI-2012 FEV₁ predicted reference equations. Subfigures (A–D) represent the assessments of CAT scores (A), mMRC grades (B), CCQ scores (C), AE histories in the last year (D) of GOLD grades under the two FEV₁ predicted reference equations respectively. Data were collected from 597 patients who were diagnosed with COPD by GOLD 0.7 fixed ratio and both the GLI-2012 and GIRH-2017 LLN diagnosis thresholds. Data were shown as the mean with standard error. t-test was used for statistical analysis.

Abbreviations: AE, acute exacerbation; AFL, airflow limitation; CAT, COPD Assessment Test; CCQ, COPD Clinical Questionnaire; COPD, Chronic Obstructive Pulmonary Disease; FEV₁, forced expiratory volume in one second; GOLD, Global initiative for chronic obstructive pulmonary disease; GLI, Global Lung Function Initiative; GIRH, Guangzhou Institute of Respiratory Health; LLN, Lower Limit of Normal; mMRC, the modified British Medical Research Council.

Figure 3 ABCD assessment scheme in every GOLD grade with GIRH-2017 and GLI-2012 FEV₁ predicted reference equations. Data were collected from 597 patients who were diagnosed with COPD by GOLD 0.7 fixed ratio and both the GLI-2012 and GIRH-2017 LLN diagnosis thresholds. Chi-square test was used for comparison of ABCD groups distribution with the two reference equations.

Abbreviations: COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in one second; GOLD, Global initiative for chronic obstructive pulmonary disease; GLI, Global Lung Function Initiative; GIRH, Guangzhou Institute of Respiratory Health; LLN, Lower Limit of Normal.