3. 1 Baseline Characteristics of Participants
Among the 5, 807 participants analyzed in this study, 550 were diagnosed with COPD (9.47%). The eligible subjects had an average age of 50.61 ± 17.20 years, with 2, 880 females and 2, 927 males. The study revealed that, when compared with the non-COPD group, the COPD group exhibited higher proportions of males, non-Hispanic whites, individuals with a high school education or above, widowed/divorced/separated individuals, smokers, drinkers, and those with underlying diseases (such as hypertension, diabetes, and coronary heart disease) (p < 0.05). Moreover, there were statistically significant differences between the two groups in terms of age, PIR, BMI, and NPAR levels (p < 0.05). The general characteristics of the study population are detailed in Table 1.
TABLE 1 Basic characteristics of participants (n =5807) in the NHANES 2017–2020.
Outcomes
|
Total, N = 5807(100%)
|
Non-COPD, N = 5257 (93%)
|
COPD, N = 550 (7. 3%)
|
P-value
|
Age (years)
|
50.62 ± 17.27
|
49.63 ± 17.20
|
60.05 ± 14.89
|
<0.001
|
PIR
|
2.66 ± 1.63
|
2.72 ± 1.63
|
2.09 ± 1.43
|
<0.001
|
BMI (kg/m2)
|
30.23 ± 7.63
|
30.05 ± 7.38
|
31.98 ± 9.55
|
<0.001
|
NAPR
|
14.20 ± 2.85
|
14.11 ± 2.80
|
15.12 ± 3.15
|
<0.001
|
Gender
|
|
|
|
0.202
|
Male
|
2927 (50.40%)
|
2664 (50.68%)
|
263 (47.82%)
|
|
Female
|
2880 (49.60%)
|
2593 (49.32%)
|
287 (52.18%)
|
|
Race
|
|
|
|
<0.001
|
Mexican American
|
681 (11.73%)
|
662 (12.59%)
|
19 (3.45%)
|
|
Other Hispanic
|
565 (9.73%)
|
532 (10.12%)
|
33 (6.00%)
|
|
Non-Hispanic White
|
2276 (39.19%)
|
1946 (37.02%)
|
330 (60.00%)
|
|
Non-Hispanic Black
|
1456 (25.07%)
|
1344 (25.57%)
|
112 (20.36%)
|
|
Other Race
|
829 (14.28%)
|
773 (14.70%)
|
56 (10.18%)
|
|
Education level
|
|
|
|
<0.001
|
Less than high school
|
906 (15.60%)
|
801 (15.24%)
|
105 (19.09%)
|
|
High school
|
1402 (24.14%)
|
1229 (23.38%)
|
173 (31.45%)
|
|
More than high school
|
3499 (60.25%)
|
3227 (61.38%)
|
272 (49.45%)
|
|
Marital Status
|
|
|
|
<0.001
|
Married/Living with Partner
|
3410 (58.72%)
|
3135 (59.63%)
|
275 (50.00%)
|
|
Widowed/Divorced/Separated
|
1315 (22.65%)
|
1121 (21.32%)
|
194 (35.27%)
|
|
Never married
|
1082 (18.63%)
|
1001 (19.04%)
|
81 (14.73%)
|
|
Smoke status
|
|
|
|
<0.001
|
Now
|
1110 (19.11%)
|
911 (17.33%)
|
199 (36.18%)
|
|
Never
|
3162 (54.45%)
|
3025 (57.54%)
|
137 (24.91%)
|
|
Former
|
1535 (26.43%)
|
1321 (25.13%)
|
214 (38.91%)
|
|
Alcohol
|
|
|
|
<0.001
|
Yes
|
2802 (48.25%)
|
2469 (46.97%)
|
333 (60.55%)
|
|
No
|
3005 (51.75%)
|
2788 (53.03%)
|
217 (39.45%)
|
|
Hypertension
|
|
|
|
<0.001
|
Yes
|
3586 (61.75%)
|
3352 (63.76%)
|
234 (42.55%)
|
|
No
|
2221 (38.25%)
|
1905 (36.24%)
|
316 (57.45%)
|
|
Diabetes
|
|
|
|
<0.001
|
Yes
|
4734 (81.52%)
|
4356 (82.86%)
|
378 (68.73%)
|
|
No
|
1073 (18.48%)
|
901 (17.14%)
|
172 (31.27%)
|
|
CHD
|
|
|
|
<0.001
|
Yes
|
5537 (95.35%)
|
5072 (96.48%)
|
465 (84.55%)
|
|
No
|
270 (4.65%)
|
185 (3.52%)
|
85 (15.45%)
|
|
Results are shown as N (%) for binary variables, and as mean ± standard deviation (SD) for continuous variables. Bold values indicate p-value < 0.05.
NHANES, National Health and Nutrition Examination Survey; COPD, Chronic Obstructive Pulmonary Disease; PIR, Poverty Income Ratio; BMI, Body Mass Index; NPAR, Neutrophil percentage-to-albumin ratio;CHD,Coronary heart disease.
3. 2 Relationship Between NAPR and COPD
Table 2 presents the correlation between NAPR and COPD. The findings reveal a positive correlation between the NAPR index and COPD. In the unadjusted model, a one-unit increase in NAPR was associated with a 13% increase in the prevalence of COPD (OR=1.13; 95% CI: 1.09~1. 16, P<0.001). Model 1, which adjusted for gender, age, and race, showed a consistent relationship between NAPR and COPD (OR=1.10; 95% CI: 1.06~1.13, P<0.001). Even in the fully adjusted Model 2, which accounted for various factors including age, gender, race, education level, marital status, PIR, BMI, smoking status, drinking status, hypertension, diabetes, and coronary heart disease, the correlation between NAPR and COPD remained significant (OR=1.05; 95% CI: 1.01~1.08, P=0.007). Model 2 also revealed that individuals in the highest quartile of NAPR (Q4) had a 34% higher risk of developing COPD compared to those in the lowest quartile (Q1) (OR=1.34; 95% CI: 1.01~1. 77, P=0.039). Furthermore, the study observed a trend of increasing prevalence of COPD with higher NAPR levels (P for trend =0.015).
TABLE 2 The associations between NAPR and COPD
Exposure
|
Non-adjusted
|
Adjust I
|
Adjust II
|
OR (95% CI)
|
p-value
|
OR (95% CI)
|
p-value
|
OR (95% CI)
|
p-value
|
NAPR
|
1.13 (1.09, 1.16)
|
<0.001
|
1.09 (1.06, 1.13)
|
<0.001
|
1.05 (1.01, 1.08)
|
0.007
|
Q1
|
Ref
|
|
Ref
|
|
Ref
|
|
Q2
|
1.07 (0.80, 1.43)
|
0.636
|
0.99 (0.73, 1.33)
|
0.926
|
0.96 (0.71, 1.31)
|
0.811
|
Q3
|
1.56 (1.19, 2.04)
|
0.001
|
1.24 (0.94, 1.65)
|
0.124
|
1.08 (0.81, 1.45)
|
0.584
|
Q4
|
2.41 (1.87, 3.10)
|
<0.001
|
1.79 (1.37, 2.33)
|
<0.001
|
1.34 (1.01, 1.77)
|
0.039
|
P for trend
|
<0.001
|
<0.001
|
0.015
|
Non-adjusted model adjust for: None ;
Adjust I model adjust for: Gender; Age ;Race;
Adjust II model adjust for: Gender;Age ; Race; Education level; Marital Status; Income to poverty ratio; BMI; Smoke status; Alcohol; Hypertension; Diabetes; Coronary heart disease;BMI was classified as normal (<25kg/m2), overweight (≥25kg/m2, <30kg/m2) and obese (≥30 kg/m2).
NPAR, Neutrophil percentage-to-albumin ratio;Ref, Reference; OR,odds ratio. 95%CI,95% confidence interval; Q1-4 respectively represent the groups divided according to the quantiles of NAPR.
3. 3 Smoothing Curve Fitting and Threshold Effect Analysis
A smoothing curve fitting model was utilized, revealing a non-linear correlation between NAPR and the prevalence of COPD, as illustrated in Figure 2. Below the inflection point of 16. 34, NAPR did not exhibit a statistically significant difference with COPD (OR=1.02, 95% CI: 0.96-1.07, P=0.577); however, above the inflection point, NAPR demonstrated a significant positive correlation with COPD (OR=1.20, 95% CI: 1.10-1.31, P<0.001). The results of the Log-likelihood ratio test further supported these findings (P=0.007) as shown in Table 3.
TABLE 3 Two-piecewise linear regression explained the threshold effect analysis of NAPR with COPD prevalence
NAPR
|
Adjusted β(95% CI), P-value
|
ULR Test
|
1.07 (1.03, 1.11) < 0.001
|
PLR Test
|
Inflection point
|
16.34
|
NAPR < 16.34
|
1.02 (0.96, 1.07) 0.577
|
NAPR ≥ 16.34
|
1.20 (1.10, 1.31) < 0.001
|
|
LRT
|
0.007
|
Adjust for: Gender;Age ; Race; Education level; Marital Status; Income to poverty ratio; BMI;Smoke status; Alcohol; Hypertension; Diabetes; Coronary heart disease;BMI was classified as normal (<25kg/m2), overweight (≥ 25kg/m2, < 30kg/m2) and obese (≥ 30 kg/m2).
NPAR, Neutrophil percentage-to-albumin ratio; ULR, univariate linear regression; PLR, piecewise linear regression; LRT, logarithmic likelihood ratio test; 95%CI,95% confidence interval; statistically significant: P = 0.007.
3. 4 Subgroup Analysis and Interaction Test
A subgroup analysis (Figure 3) was conducted to explore potential variations in the association between NAPR and COPD across different populations. Following adjustment for all covariates, NAPR showed a significant relationship with COPD incidence in subgroups including males, individuals aged over 40, those with a BMI < 25 kg/m2, former smokers, drinkers, and non-coronary heart disease patients (all P < 0.05). Moreover, irrespective of hypertension or diabetes status, the subgroup analysis revealed a notable correlation between NAPR and COPD incidence (all P < 0.05). Interaction tests indicated that age, gender, race, BMI, smoking status, drinking status, hypertension, diabetes, and coronary heart disease did not significantly impact this relationship (P for interaction > 0.05).