Table 4

Multivariable linear regression models for FEV1 and FVC z-scores in 255 patients with sickle cell anaemia aged 6–18 years from Nigeria (n=154) and the UK (n=101)

Covariate*FEV1 z-score†FVC z-score†
Adjusted B
(95% CI; p value)		Adjusted B
(95% CI; p value)
Male sex0.26
(0.04 to 0.49; 0.02)		0.20
(−0.18 to 0.42; 0.07)
Age, years−0.09
(−0.12 to −0.05; <0.001)		−0.08
(−0.11 to −0.04; <0.001)
zBMI0.26
(0.17 to 0.35; <0.001)		0.29
(0.21 to 0.38; <0.001)
No hydroxyurea therapy−0.27
(−0.59 to 0.04; 0.09)		−0.30
(−0.62 to 0.00; 0.05)
Previous acute chest syndrome‡−0.41
(−0.67 to −0.17; 0.001)		−0.35
(−0.60 to −0.11; 0.004)

  • zBMI values are based on WHO growth charts.25

  • Spirometry z-scores are based on Global Lung Function Initiative 2012 equations for African–Americans.26

  • *Only the variables presented in the table were retained in the final models, whereas the original models also included the covariates ‘residency in Nigeria’ and ‘at least three pain crises in the last year’ that were excluded through a stepwise backward approach based on a p value<0.2.

  • †Adjusted R2 of the models: 0.25 for zFEV1 and 0.27 for zFVC.

  • ‡Fever and/or respiratory symptoms, plus a new pulmonary infiltrate on a chest X-ray.22

  • zBMI, z-score body mass index; zFEV1, z-score FEV1; zFVC, z-score FVC.