Sickle cell disease (SCD) is the most common among the inherited blood diseases, and its prevalence is rising worldwide. People with SCD often have abnormal lung function [9], which can lead to other health problems and a lower quality of life.

Our goal was to determine how common lung function problems are among young individuals with SCD. The results indicate a concerning trend that children with SCD seem to be at a higher risk for compromised lung function.

Lung function tests using spirometry showed that nearly a third (28%) of the SCD patients in this study had impairments. This finding is supported by another study conducted on Kuwaiti children with SCD (average age 10.5 years). The study reported that 26.3% of the SCD patients evaluated exhibited problems or changes in their lung function [10].

In the current study, changes in pulmonary functions could be observed as young as 8 years old (this was the youngest age group included in our study). The obstructive pattern (n = 5, 8.3%) was more prevalent in the younger patients (mean age = 10.8 years ± 1.6SD); however, the restrictive pattern (n = 10, 16.7%) was generally predominant among the total study population (mean age = 11.4 ± 2.2 SD).

A comparable study on 64 children (8–15 years old) found abnormal spirometry results in 15 patients (23.4%) [11]. These results included restrictive lung disease (n = 8, 12.5%) and obstructive lung disease (n = 7, 10.9%). Contrarily, in another study held on Kuwaiti SCD children, with a mean age of 10.5 years, there was a predominant obstructive pattern, but this may be because the studied age group was relatively younger [10]. Airflow restriction is frequently detected in SCD children undergoing spirometry [12]. The obstructive lung finding may be caused by pulmonary vascular engorgement compressing the distal airways as well as airway remodeling and inflammation associated with vascular occlusion together with hemolysis in the pulmonary microcirculation [13, 14]. However, research on SCA in adults and adolescents reveals that a restrictive physiology emerges with aging, most likely as a result of cumulative lung damage [15].

In our study, patients showing restrictive pulmonary function test had a significantly lower BMI Z score (p-value = 0.021) when compared with those SCD with normal PFT, contrary to another study that revealed a higher prevalence of obstructive spirometry in UK-based patients with SCA (hemoglobin SS phenotype) aged 6–18 compared with their Nigerian counterparts. This finding aligns with the observation that Black African children with SCA residing in low-income settings exhibited a more frequent restrictive spirometry pattern, suggesting a disparity in lung function presentations across income levels.

A Nigerian study involving 113 adults and children with sickle cell disease (SCD) found no correlation between body mass index (BMI) and lung function [16]. However, this research also showed that SCD patients had generally lower BMIs and lung function compared with healthy individuals [17]. Importantly, over 40% of the SCD patients had abnormal lung function, with the most frequent abnormality being a restrictive pattern (almost 28%) [17]. In children with SCD, a restrictive lung function pattern suggests a potentially more serious form of chronic lung disease [16].

Research suggests that frequent bone infarctions in the spine, breastbone, and ribs can restrict chest wall growth in SCD patients. This limitation may hinder their overall development and potentially cause reduced lung capacity [16].

Patients with sickle cell disease (SCD) and restrictive lung disease received higher hydroxyurea dosages compared with those with normal lung function (p-value = 0.022). This finding suggests a possible link between higher hydroxyurea dosage and greater disease severity. It could be that patients who require higher hydroxyurea doses have a more advanced stage of the disease and experience more complications [16]. Research from high-income countries has shown that hydroxyurea use improves lung function in patients with SCD in the long term [18].

This study found a trend towards lower hemoglobin levels in the group with restrictive lung function, although this was not statistically significant. This aligns with another study on African children with SCA, which showed a link between low hemoglobin and a restrictive spirometry pattern [16].

Studying the relationship between lung functions (FEV1, FVC, FEV1/FVC ratio) and other clinical data, there was a weak positive correlation between FEV1 and body mass index (BMI) percentile (r = 0.15, p = 0.24), but this was not statistically significant. This is similar to another study that used a more complex statistical model and found that lung function (FEV1) improves with increasing BMI, but only up to a certain point [19]. Additionally, research by Arigliani et al. suggests that SCA patients with wasting are more likely to have restrictive spirometry patterns [16].

Furthermore, our research identified a weak negative correlation between FVC and increased levels of HbS (r =  − 0.277, p = 0.032). This suggests a connection between HbSS severity (higher HbS) and restrictive lung disease (lower FVC). Klings et al. provide further explanation for this association [20]. Additionally, a separate Ghana study involving HbSS patients found a significantly higher risk of abnormal lung function compared with healthy individuals [21]. Therefore, HbS increases the chances of having problems with lung function and reduced lung volume.

In a previous study, Lunt et al. found that SCA patients with lower hemoglobin levels had more engorged lung capillaries together with higher resistance to airflow, suggesting a mixed pathology [22]. They proposed that blood vessel congestion in the lungs squeezed the small airways from outside, resulting in the increased resistance of the airways. It is possible a similar process is happening in our patients. The fact that a restrictive spirometry pattern was more common might indicate more severe chronic lung damage in Egyptian children with SCA compared with those in the UK.

This study also found that lung function measurements, FEV1 and FVC, decreased as both the dosage of hydroxyurea (HU) and the frequency of blood transfusions increased. This correlation was statistically significant (p-values < 0.05). These findings contradict a previous study on 38 Kuwaiti children with sickle cell disease (SCD) that did not observe any association between lung function and HU use or blood transfusions [10]. It is important to note that the previous study had a smaller sample size (n = 38) and compared children with SCD to healthy controls, whereas this study focused solely on individuals with SCD.