Cut-off value of FEV₁/FEV₆ as a surrogate for FEV₁/FVC for detecting airway obstruction in a Korean population

Figures & data

Table 1 Baseline characteristics of the study population

	Male	Female	Total
Subject, n (%)	6,515 (43.5)	8,463 (56.5)	14,978 (100)
Age (years)	56.9±10.9	57.0 ±10.6	57.0±10.7
Age group (years)
40–49	1,944 (29.8)	2,342 (27.7)	4,286 (28.6)
50–59	1,922 (29.5)	2,739 (32.4)	4,661 (31.1)
60–69	1,625 (24.9)	2,077 (24.5)	3,702 (24.7)
≥70	1,024 (15.7)	1,305 (15.4)	2,329 (15.5)
Height (cm)	168.4±6.0	155.4±5.8	161.0±8.7
Weight (Kg)	69.0±9.7	58.3±8.4	62.9±10.5
BMI (Kg/m^2)	24.3±2.8	24.1±3.2	24.2±3.0
Pulmonary function test
FEV1 (L)	3.11±0.66	2.33±0.45	2.67±0.67
FEV1 (%, pred)	89.79±13.69	94.40±12.95	92.40±13.47
FVC (L)	4.15±0.69	2.93±0.50	3.46±0.85
FVC (%, pred)	91.52±11.65	94.10±11.57	92.98±11.67
FEV1/FVC (%)	0.75±0.08	0.79±0.06	0.77±0.08
FEV6 (L)	3.98±0.71	2.87±0.50	3.35±0.82
FEV1/FEV6 (%)	0.78±0.07	0.81±0.05	0.80±0.06
Normal	4,291 (65.9)	7,145 (84.4)	11,436 (76.4)
Restricted	688 (10.6)	750 (8.9)	1,438 (9.6)
Obstructed	1,536 (23.6)	568 (6.7)	2,104 (14.1)
GOLD stage I	740 (11.4)	278 (3.3)	1,018 (6.8)
GOLD stage II	731 (11.2)	265 (3.1)	996 (6.6)
GOLD stage III	57 (0.9)	23 (0.3)	80 (0.5)
GOLD stage IV	8 (0.1)	2 (0.0)	10 (0.1)

Notes: Data are presented as numbers (percentages) for categorical variables. Continuous variables are presented as means ± standard deviations.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FEV₆, forced expiratory volume in 6 seconds; FVC, forced vital capacity; BMI, body mass index; pred, predicted; GOLD, Global Initiative for Chronic Obstructive Lung Disease.

Table 2 Sensitivities and specificities of thresholds of FEV₁/FEV₆ for predicting FEV₁/FVC <70%

FEV1/FEV6 ratio	Sensitivity	Specificity	PPV	NPV	Accuracy	Kappa value (95% CI)
<70	44.1	100.0	100.0	91.6	92.2	0.576 (0.554–0.598)
<73	74.2	98.9	91.6	95.9	95.4	0.794 (0.778–0.810)
<75	93.8	94.8	74.7	98.9	94.7	0.800 (0.786–0.814)
<76	98.0	90.8	63.6	99.6	91.8	0.724 (0.710–0.738)

Note: Data are presented as percentages.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FEV₆, forced expiratory volume in 6 seconds; FVC, forced vital capacity; PPV, positive predictive value; NPV, negative predictive value; CI, confidence interval.

Table 3 Comparison of FEV₁/FEV₆ with FEV₁/FVC for diagnosing airway obstruction

	FEV1/FEV6#		Totals
	No obstruction	Obstruction
FEV1/FVC§
No obstruction	12,204 (94.8)	670 (5.2)	12,874 (86.0)
Obstruction	130 (6.2)	1,974 (93.8)	2,104 (14.0)
Totals	12,334 (82.3)	2,644 (17.7)	14,978 (100)

Notes: Data are presented as numbers (percentages);

§ using FEV₁/FVC <70% as a fixed cut-off;

# using FEV₁/FEV₆ as a fixed cut-off <75%; prevalence of obstruction =17.7%, Kappa value =0.80, 95% CI 0.79–0.81, P<0.001.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FEV₆, forced expiratory volume in 6 seconds; FVC, forced vital capacity; CI, confidence interval.

Table 4 Comparison of FEV₁/FEV₆ with FEV₁/FVC for the diagnosis of normal, restricted, and obstruction patterns

	FEV1/FEV6#		Totals
	No obstruction	Obstruction
FEV1/FVC§
Normal	10,862 (95.0)	574 (5.0)	11,436 (76.4)
Restricted	1,342 (93.3)	96 (6.7)	1,438 (9.6)
Obstructed	130 (6.2)	1,974 (93.8)	2,104 (14.1)
GOLD stage I	102 (10.0)	916 (90.0)	1,018 (6.8)
GOLD stage II	28 (2.8)	968 (97.2)	996 (6.6)
GOLD stage III	0 (0)	80 (100)	80 (0.5)
GOLD stage IV	0 (0)	10 (100)	10 (0.1)
Totals	12,334 (82.3)	2,644 (17.7)	14,978 (100)

Notes: Data are presented as numbers (percentages);

§ using FEV₁/FVC <70% as a fixed cut-off;

# using FEV₁/FEV₆ as a fixed cut-off <75%.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FEV₆, forced expiratory volume in 6 seconds; FVC, forced vital capacity; GOLD, Global Initiative for Chronic Obstructive Lung Disease.

Figure 1 A receiver operating characteristic (ROC) curve showing the ability of FEV₁/FEV₆ to diagnose FEV₁/FVC <70%.

Notes: Area under the ROC curve is 0.989 (95% confidence interval, 0.987–0.990). The best cut-off value is 0.75 with 0.971% sensitivity and 0.927% specificity.
Abbreviations: FEV₁, forced expiratory volume in 1 second; FEV₆, forced expiratory volume in 6 seconds; FVC, forced vital capacity; AUC, area under the curve.

Table 5 Comparison of FEV₁/FVC LLN with FEV₁/FVC <70% or FEV₁/FEV₆ <75%

	FEV1/FVC LLN*		Totals
	No obstruction	Obstruction
FEV1/FVC§
No obstruction	12,857 (99.9)	11 (0.1)	12,868 (85.9)
Obstruction	1,030 (49.0)	1,074 (51.0)	2,104 (14.1)
FEV1/FEV6#
No obstruction	12,327 (100.0)	1 (0.0)	12,328 (82.3)
Obstruction	1,560 (59.0)	1,084 (41.0)	2,644 (17.7)
Totals	13,887 (92.8)	1,085 (7.2)	14,972 (100)

Notes: Data are presented as numbers (percentages);

* lower limit of normal using ERS/GLI 2012 equations;

§ using FEV₁/FVC <70% as a fixed cut-off;

# using FEV₁/FEV₆ as a fixed cut-off <75%.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FEV₆, forced expiratory volume in 6 seconds; FVC, forced vital capacity; LLN, lower limit of normal; ERS, European Respiratory Society; GLI, Global Lung Initiative.

Table 6 Age and forced expiratory volume in 1 second (FEV₁) dependency of the lower limit of normal (LLN) for FEV₁/forced vital capacity (FVC) and FEV₁/forced expiratory volume in 6 seconds (FEV₆) in airway obstruction

	FEV1/FVC <LLN	FEV1/FVC <70%	FEV1/FEV6 <75%	ΔFEV1/FVC*	ΔFEV1/FEV6§	Δ(FEV1/FEV6−FEV1/FVC)#
	1,085 (7.2)	2,104 (14.1)	2,644 (17.7)	14,972 (100)	14,972 (100)	14,972 (100)
Age group (years)
40~49	153 (3.6)	151 (3.5)	310 (7.2)	10.5±5.2	11.8±4.6	1.3±1.2
50~59	278 (6.0)	417 (8.9)	594 (12.7)	9.9±6.0	12.0±4.9	2.1±1.7
60~69	361 (9.8)	766 (20.7)	888 (24.0)	9.0±8.4	12.3±5.7	3.1±2.3
70~	293 (12.6)	770 (33.1)	852 (36.6)	9.7±6.6	12.6±5.3	3.7±2.8
FEV1 (%)
>80	336 (2.6)	1,018 (8.0)	1,409 (11.1)	11.0±5.1	13.9±4.2	2.1±1.8
50~80	661 (30.3)	996 (45.6)	1,144 (52.4)	3.4±8.0	7.3±6.2	3.9±2.8
30~50	78 (89.7)	80 (92.0)	81 (93.1)	−15.7±10.9	−7.5±8.1	8.2±4.1
<30	10 (100.0)	10 (100.0)	10 (100.0)	−29.8±7.9	−19.9±5.4	9.9±3.3

Notes: Data are presented as numbers (percentage) or mean ± standard deviations;

* difference between LLN (%) and FEV₁/FVC (%),

§ difference between LLN (%) and FEV₁/FEV₆(%);

# difference between FEV₁/FEV₆ (%) and FEV₁/FVC (%).

Figure 2 FEV₁/FVC LLN, FEV₁/FVC, FEV₁/FEV₆, and the mean difference between FEV₁/FEV₆ and FEV₁/FVC according to the age group.

Notes: With increasing age, the mean difference between FEV₁/FEV₆ and FEV₁/FVC was increasingly larger. However, the mean difference between FEV₁/FVC LLN and FEV₁/FVC or FEV₁/FEV₆ showed only a slight difference.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FEV₆, forced expiratory volume in 6 seconds; FVC, forced vital capacity; LLN, lower limit of normal.

Figure 3 FEV₁/FVC LLN, FEV₁/FVC, FEV₁/FEV₆, and the mean difference between FEV₁/FEV₆ and FEV₁/FVC according to the FEV₁ (%) group.

Notes: With increasing severity of obstruction, the mean difference between FEV₁/FEV₆ and FEV₁/FVC was increasingly larger. The mean difference between FEV₁/FVC LLN and FEV₁/FEV₆ was larger than the mean difference between FEV₁/FVC LLN and FEV₁/FVC at mild–moderate stages of airway obstruction, but was smaller at severe and very severe stages.
Abbreviations: FEV₁, forced expiratory volume in 1 second; FEV₆, forced expiratory volume in 6 seconds; FVC, forced vital capacity; LLN, lower limit of normal.