Pneumonia is considered one of the leading infectious causes of pediatric morbidity and mortality. In 2010, 120 million cases of pneumonia were reported in children younger than 5 years, with 14 million of them proceeding to severe episodes. In 2011, a study estimated that 1.3 million cases of pneumonia deceased and 81% of deaths occurred in the first 2 years of life [8].
Investigating the association of serum leptin and pulmonary diseases in adults attracted a great interest in the past few years. A meta-analysis included ten articles that concluded a positive association between leptin and tumor necrosis factor (TNF-α) levels in COPD exacerbations in adults [9]. Moreover, other studies reported that asthma severity positively correlated with serum leptin [10, 11]. It was suggested that leptin presence is essential for an effective immune response against variable bacterial pulmonary infections [12]. Recently, research proved that leptin has a critical role in the immune system, and its deficiency results in increased severity of pulmonary infections [13]. Therefore, the present study evaluated serum leptin in CAP children.
We found that serum leptin was more elevated in severe cases of pneumonia than moderate cases. However, ROC curve analysis revealed that serum leptin fairly discriminated between moderate and severe pneumonia (AUC = 0.646).
Interestingly, in our study serum leptin showed good discriminatory ability between CAP cases admitted in PICU and those admitted in the general ward. This finding offers a good tool in the emergency department to aid in making a sound objective decision for the appropriate admission location of the patients. Up to the best of the authors’ knowledge, no previous research has studied this point.
In our study, we found a significant association between high serum leptin in the studied patients and sputum cultures growing more than one organism. This was in agreement with Mancuso et al. who reported increased leptin levels in serum, BAL fluid, and whole lung homogenates in response to intra-tracheal challenge with Klebsiella pneumonia in experimental murine models [14] Likewise, another study demonstrated upregulation of pulmonary leptin levels in both humans and mice following bacterial- and viral-induced pneumonia [15].
On the other hand, Al Biltagi et al. found that low serum leptin level was associated with pneumonia in malnourished children [16]. This may be attributed to lower serum leptin in malnourished children than in healthy controls [17, 18]. Hence, malnourished patients were excluded from our study. Another study by Diez et al. reported the lack of significant differences in leptin levels between adult patients hospitalized for community-acquired pneumonia and healthy controls, after adjusting for BMI [19].
We did not find an association between high serum leptin level and mortality from CAP. This finding is in line with comparable studies which concluded that leptin lacks prognostic value for pneumonia lethality [19] and overall all-cause mortality rates in adult males [20].
We found a significantly elevated CRP level in patients with a high serum leptin level. Moreover, the correlation between serum leptin and CRP levels in the studied patients was positive, significant, and strong. Similarly, Somech et al. reported that leptin levels significantly correlated with CRP levels during acute infections in children [21]. Likewise, a research on chronic COPD in adults studied the complex relationship between adipokine metabolism and mild systemic inflammation in chronic COPD and reported the presence of significant correlation between circulating leptin and CRP levels [22].
The present study was subject to few limitations, including the limited number of patients and the non-inclusion of mild cases of CAP as these cases were sent on home treatment from the emergency department.