Table 2. Comparison of spirometry data according to free thyroxine quartiles.
| Variables | fT4 quartile | p value | |||
|---|---|---|---|---|---|
| Q1 (0.89–1.09 ng/dL) (n = 294, 23.4%) |
Q2 (1.10–1.19 ng/dL) (n = 321, 25.5%) |
Q3 (1.20–1.30 ng/dL) (n = 317, 25.2%) |
Q4 (1.31–1.76 ng/dL) (n = 329, 25.9%) |
||
| Spirometry parameters | |||||
| FVC (L) | 3.63 (0.05) | 3.73 (0.06) | 3.79 (0.05) | 3.98 (0.05) | <0.001 |
| FVC (%, predicted) | 96.08 (0.62) | 95.71 (0.69) | 95.47 (0.58) | 95.32 (0.60) | 0.840 |
| FEV1 (L) | 2.84 (0.03) | 2.89 (0.04) | 2.92 (0.04) | 3.06 (0.04) | 0.001 |
| FEV1 (%, predicted) | 95.69 (0.63) | 94.35 (0.71) | 93.42 (0.67) | 92.78 (0.71) | 0.012 |
| FEV1/FVC | 0.786 (0.003) | 0.779 (0.004) | 0.775 (0.004) | 0.769 (0.004) | 0.004 |
| FEF25-75 (L/sec) | 2.78(0.05) | 2.74 (0.05) | 2.74 (0.06) | 2.81 (0.07) | 0.898 |
| Obstructive lung pattern (%) | 4.9% | 9.3% | 13.0% | 15.9% | <0.001 |
fT4, free thyroxine; FVC, forced vital capacity; FEV1, forced expiratory volume in one second; FEF25-75, forced expiratory flow, mid-expiratory phase.
Data are presented as means (standard error) or weighted percentages as appropriate for the variable. Spirometry data of the study population with respect to the free thyroxine quartiles were compared using general linear model for continuous variables and chi-square test for categorical variables.