TABLE 3.
Forced expiratory volume in 1 s (FEV1) of patients with primary ciliary dyskinesia (PCD) from the International PCD Cohort compared to Global Lung Function Initiative 2012 reference values (linear mixed effects regression, adjusting for all covariates)
| Estimate (95% CI) | p-value # | |
| Intercept¶ (lung function at age 6 years for “reference patient”) | −1.26 (−2.19– −0.3) | |
| Age at measurement | −0.04 (−0.12–0.04) | |
| Country (ref: Germany) | <0.01 | |
| Australia | −0.34 (−1.26–0.59) | |
| Belgium | −0.20 (−1.03–0.64) | |
| Cyprus | −1.19 (−2.14– −0.23) | |
| Czech Republic | −0.95 (−1.68– −0.22) | |
| Denmark | 0.21 (−0.42–0.84) | |
| France | 0.14 (−0.65–0.93) | |
| Greece | 0.92 (−2.35–4.19) | |
| Israel | 0.11 (−0.71–0.93) | |
| Italy | −0.28 (−1.02–0.47) | |
| The Netherlands | 1.63 (0.84–2.43) | |
| Norway | −0.31 (−1.24–0.63) | |
| Poland | −0.86 (−1.70– −0.03) | |
| Switzerland | 0.13 (−0.63–0.89) | |
| Turkey | −1.76 (−2.46– −1.06) | |
| UK | −1.09 (−1.90– −0.28) | |
| Sex (ref: male) | 0.37 | |
| Female | −0.03 (−0.33–0.27) | |
| Age at diagnosis | −0.01 (−0.05–0.02) | 0.21 |
| Diagnostic period | 0.02 (−0.005–0.05) | 0.26 |
| Diagnostic certainty (ref: definite PCD diagnosis+) | 0.49 | |
| Probable PCD diagnosis§ | −0.04 (−0.43–0.35) | |
| Clinical diagnosis only | 0.38 (−0.27–1.03) | |
| Laterality defects (ref: situs solitus) | 0.59 | |
| Ambiguous | 0.42 (−0.53–1.36) | |
| Situs inversus | 0.33 (−0.001–0.66) | |
| Unknown | 0.15 (−0.54–0.85) | |
| BMI | 0.32 (0.28–0.37) | <0.01 |
| Change of lung function over time ƒ | ||
| Country (ref: Germany) | <0.01 | |
| Australia | −0.02 (−0.10–0.07) | |
| Belgium | 0.02 (−0.05–0.10) | |
| Cyprus | 0.07 (−0.01–0.15) | |
| Czech Republic | 0.04 (−0.03–0.11) | |
| Denmark | −0.01 (−0.07–0.05) | |
| France | −0.05 (−0.12–0.03) | |
| Greece | 0.01 (−0.29–0.32) | |
| Israel | −0.05 (−0.13–0.03) | |
| Italy | −0.03 (−0.10–0.04) | |
| The Netherlands | −0.14 (−0.24– −0.04) | |
| Norway | −0.02 (−0.12–0.09) | |
| Poland | 0.04 (−0.05–0.13) | |
| Switzerland | −0.03 (−0.10–0.05) | |
| Turkey | 0.11 (0.04–0.18) | |
| UK | 0.03 (−0.04–0.11) | |
| Sex (ref: male) | 0.36 | |
| Female | −0.01 (−0.04–0.02) | |
| Age at diagnosis | 0.003 (0.00–0.01) | 0.08 |
| Diagnostic period | −0.001 (−0.004–0.001) | 0.32 |
| Diagnostic certainty (ref: definite PCD diagnosis+) | 0.92 | |
| Probable PCD diagnosis§ | −0.01 (−0.04–0.03) | |
| Clinical diagnosis only | −0.001 (−0.07–0.07) | |
| Laterality defects (ref: situs solitus) | 0.52 | |
| Ambiguous | −0.01 (−0.11–0.08) | |
| Situs inversus | −0.02 (−0.05–0.01) | |
| Unknown | −0.02 (−0.08–0.04) | |
| BMI | 0.02 (0.01–0.02) | <0.01 |
BMI: body mass index. #: likelihood ratio test p-value indicating whether the characteristic explains differences in FEV1 within the study population. ¶: describes the FEV1 of a reference patient at 6 years, who is male, from Germany, with a BMI z-score of 0, diagnosed at birth (age=0) in 1978, with a definite PCD diagnosis. Categorical variables describe the change from the reference category, while continuous variables describe the change from the reference patient for each unit of increase. +: hallmark PCD ultrastructural defect identified by electron microscopy findings or biallelic PCD causing gene mutation based on the European Respiratory Society PCD diagnosis guidelines [19]. §: abnormal light or high-frequency video microscopy finding and/or low (≤77 nL·min−1) nasal nitric oxide value. ƒ: based on interaction terms between the characteristics (e.g. country, sex) and age. Change of lung function over time thus describes the change in the trajectory of FEV1 per year increase, based on the reference category for categorical variables and for each unit of increase for continuous variables.