Introduction

    Zinc is a vital trace element that serves as a catalytic cofactor for over 300 metalloenzymes, driving DNA synthesis, protein translation, and cellular proliferation. It maintains metabolic homeostasis, supports neurocognitive processes, and regulates reproductive endocrinology. In the immune system, zinc orchestrates leukopoiesis and lymphopoiesis—guiding the proliferation, differentiation, and maturation of neutrophils, macrophages, and T- and B-lymphocytes—while fine-tuning cytokine production and optimizing phagocytic activity. (1)

     Zinc—the body’s second-most plentiful trace mineral after iron—is indispensable for maintaining immune system competence. Because it cannot be synthesized endogenously, sufficient zinc must be obtained through the diet.(2,3)

  Zinc confers immune-protection by modulating key cytokines, such as Interleukin-6 (IL-6), Tumor Necrosis Factor-alpha (TNF-α), Interleukin-2 (IL-2), and Interleukin-10 (IL-10), attenuating oxidative stress, and reinforcing the barrier and antimicrobial functions of the respiratory epithelium. (4,5) 

       Zinc deficiency has been implicated in a heightened risk of respiratory tract infections, most notably pediatric pneumonia in children under five, which continues to stand as a primary driver of global under-five mortality.(6)

Despite the established link between zinc and immune function, little is known about how serum zinc concentrations correlate with pneumonia severity in hospitalized children, especially when comparing those admitted to intensive care versus general wards. This study addresses that gap by measuring serum zinc levels in pediatric patients with community-acquired pneumonia and analyzing their associations with disease severity, clinical outcomes, and mortality risk.

Patients and Methods

A cross-sectional observational study was conducted over six months (October 2021 to April 2022) at Cairo University Children's Hospital. Ethical research protocol approval was granted by the Cairo University ethical committee (approval code: MS-363-2021, date: 19-8-2021). Informed consent was obtained from participants and/or their legal guardians before enrollment.

The study included 80 children with CAP from consecutive admissions over 6 months, categorized into two groups: Group 1 (n=40) admitted to the PICU, and Group 2 (n=40) admitted to the ward. Inclusion criteria required patients aged between one month and 15 years. Exclusion criteria included cognitive impairments, congenital heart diseases, chronic illnesses, chronic upper and lower respiratory tract infections, and zinc supplementation.

Clinical assessment included respiratory distress grading and body measurements analyzed using the WHO and CDC growth charts (7–9). Pneumonia diagnosis and severity determination were classified per WHO guidelines (10). PRISM, SOFA, and Glasgow Coma Scale (GCS) scores were calculated for all patients (11–13).  Sepsis and its classifications were defined per Obonyo et al. (14)

The study measured serum zinc levels within 24 hours of admission using a Zincon-based colorimetric method. Zinc in the sample binds to 2-carboxy-2′-hydroxy-5-sulfoformazylbenzene at alkaline pH, forming a complex detected at 610 nm. Serum sample on heparin plasma acceptable; EDTA not allowed. The normal range: is 16–25 mmol/L (109–167 mg/dl). The reagents are Carbonate buffer (pH 9.5) and zincon (0.05 mM/L). Samples are incubated at 25°C for 10 minutes, and absorbance is measured. Zinc contamination from glassware and rubber caps must be avoided.

The method provides accurate and stable zinc measurement, with linearity up to 153 mmol/L (1000 mg/dl). Radiological assessments included chest X-rays and CT scans, with pneumonia diagnosis confirmed by consolidation per the British Thoracic Society guidelines (15)

Ethics approval and consent to participate

     The study protocol was approved by the Ethical Scientific Committee of the Faculty of Medicine (code: MS-363-2021, date: 19-8-2021), and per the Declaration of Helsinki for medical research involving human subjects. Informed consent was obtained from patients’ legal guardians before enrolling patients in the study.

Statistical analysis:

Statistical analysis was performed using SPSS (Statistical Package for the Social Sciences) version 22 (IBM Corp., Armonk, NY, USA). Descriptive data were presented as means, medians, and standard deviations. Comparative tests included the chi-square test, Fisher's exact test, independent t-tests, Mann-Whitney U test, and ANOVA. Correlations were assessed using Pearson's and Spearman's correlation coefficients. ROC curves were constructed for zinc's predictive power regarding pneumonia severity and clinical outcomes. A p-value <0.05 was considered statistically significant.

 Results:The study investigated serum zinc levels in pediatric patients diagnosed with community-acquired pneumonia (CAP) and their correlation with pneumonia severity and clinical outcomes. A total of 80 children were recruited from consecutive admissions over 6 months, divided equally into two groups: Group 1 (n=40) was admitted to the pediatric intensive care unit (PICU) due to severe pneumonia, and Group 2 (n=40) managed in the hospital ward with less severe pneumonia.

Table (1) shows a homogenous distribution of the age and sex of the studied patients among both groups PICU and ward, with no significant differences (p>0.05). The medians of the age were 4.5 and 6.5 months in groups PICU and ward, respectively. Males comprised 47.5% of the PICU group compared to 65.0% in the ward group, while females constituted 52.5% of the PICU group versus 35.0% of the ward group.The anthropometric measurements are shown in table (1). The medians of the weight and Z-score of the weight were non-significantly different between both groups (PICU and ward). Similarly, the height classification showed a homogenous distribution of mild, moderately, and severely stunted children among the studied groups, with no significant difference (p=0.954). The mean BMI was 17.99±3.31 in the PICU group and 18.92±2.94 in the ward group, with no significant difference (p=0.189).

The mean serum zinc level in the PICU group was significantly lower (62.05 ± 14.83 µg/dl) than in the ward group (133.25 ± 27.05 µg/dl) with a highly significant difference (p<0.001). The median CRP was significantly higher in the PICU group than in the ward group p=0.001. The degree of respiratory distress ranged between grades 3 and 4 in the PICU group, while the ward group showed grades 1 and 2, (p<0.001). (Table 2)

Group 1 had a median PRISM score, Predicted death rate score, SOFA score, and a median GCS of 11.5, 8.4, 6.0, and 13.0 respectively. 55.0% needed MV, and the median duration of mechanical ventilation (MV) was 18 days. 35% of the PICU group needed inotropes, and the most frequently used inotrope was adrenaline 12.5%. (Table 3)

Sepsis and severe sepsis were almost equally distributed among both groups; however, septic shock was only in the PICU (p=0.007). All mortalities occurred in the PICU. The median duration of stay in the PICU was 18.0 days, and 12.0 days in the ward. (Table 4)

PICU patients with sepsis, severe sepsis, and septic shock exhibited progressively lower serum zinc levels. Mechanical ventilation (MV) requirements were associated with lower zinc levels (56.42 ± 13.37 mg/dl) compared to non-ventilated patients (68.93 ± 13.89 mg/dl) (p=0.006). Patients requiring inotropic support also showed lower serum zinc levels (54.36 ± 13.85 µg/dl) compared to those not requiring inotropes (66.19 ± 13.88 mg/dl) (p=0.014). (Table 5)

PICU patients with a prolonged stay of ≥18 days exhibited significantly lower zinc levels (57.45 ± 13.42 mg/dl) compared to those with shorter stays (p=0.028). Similarly, ward patients with a prolonged stay of ≥12 days had lower zinc levels (123.10 ± 25.17 mg/dl) compared to those with shorter stays (142.44 ± 25.89 mg/dl) (p=0.022). All mortalities occurred in the PICU group, with a 30% mortality rate. Non-survivors had significantly lower zinc levels (51.60 ± 11.65 mg/dl) compared to survivors (66.53 ± 13.90 mg/dl) (p=0.002). (Table 5)

Serum zinc levels were inversely correlated with the grade of respiratory distress (r = -0.451), indicating more severe respiratory distress in children with lower zinc levels. A weak negative correlation was observed between zinc levels and both the SOFA score (r = -0.349) and PRISM score (r = -0.319), indicating more severe disease presentations were associated with lower zinc levels. (Table 6)

 Serum zinc levels showed a moderate negative correlation with CRP in both groups (PICU: r = -0.775, p<0.001; Ward: r = -0.567, p<0.001). Zinc showed significant negative correlations with TLC and platelet counts in the ward group only. (Table 6)

Zinc levels ≤88.9 mg/dl predicted severe pneumonia with 100% sensitivity and 92.5% specificity (AUC=0.983, p<0.001). (Figure 1 & Table 7). Zinc cut-off ≤64.41 mg/dl predicted the need for MV with 77.27% sensitivity and 72.22% specificity (AUC=0.744, p=0.003). (Figure 2, Table 7). Serum zinc level at a cut-off ≤68.44mg/dl demonstrated good power for predicting the need for inotropes (AUC=0.732, p=0.007). (Figure 3, Table 7). Zinc cut-off ≤68.44 mg/dl predicted mortality with 100% sensitivity and 50% specificity (AUC=0.793, p<0.001). (Figure 4, Table 7).

  Discussion

Pneumonia continues to rank among the foremost causes of childhood death worldwide. In 2019 alone, it claimed over 700,000 lives of children under five, representing 14 percent of all fatalities in that age group, and accounted for more than 22 percent of deaths in older children. The greatest burden falls on Southern Asia and sub-Saharan Africa. Preventive interventions, such as ensuring adequate nutritional status and providing vitamin and micronutrient supplementation, can substantially lower the incidence of pneumonia.(16,17)

 Preventive zinc supplementation has been shown to reduce pneumonia incidence in children by enhancing host defense mechanisms. Zinc is integral to adaptive immunity, promoting immunoglobulin G production, intracellular pathogen clearance, cytokine secretion, and phagocytic activity. (4)

Zinc also functions as a crucial antioxidant and cytoprotective agent, mitigating damage caused by toxins and inflammatory mediators to the respiratory epithelium. Even mild to moderate zinc deficiency can compromise immune competence, leading to reduced infection resistance and impaired T-lymphocyte function (5)

In this study, we measured serum zinc concentrations on admission in children with community-acquired pneumonia, comparing those admitted to the PICU with those managed on the general ward. We found that lower zinc levels at presentation were significantly correlated with greater disease severity, longer hospital stays, increased need for mechanical ventilation and inotropic support, and higher mortality risk.

Consistent with prior research linking zinc deficiency to severe respiratory infections, children in the PICU demonstrated markedly lower serum zinc concentrations (62.05 ± 14.83 µg/dl) than those managed on the ward (133.25 ± 27.05 µg/dl). (17) Studies have also shown that children with severe pneumonia and pronounced respiratory distress have significantly lower serum zinc levels, highlighting zinc’s immunomodulatory capacity to lessen infection severity. (5,19–21)

Zinc is indispensable for both innate and adaptive immunity, driving lymphocyte proliferation, cytokine secretion, and phagocytic clearance. When zinc levels fall, these defenses are compromised, impairing the host’s ability to contain infection. In our cohort, children admitted to the PICU with lower serum zinc on presentation experienced more severe clinical courses and higher mortality. These findings mirror those of Hamed et al. (2019), who similarly linked diminished zinc concentrations to poorer outcomes in pediatric pneumonia.(4,22)

Both PICU and ward cohorts exhibited a robust inverse relationship between serum zinc and C-reactive protein (PICU: r = –0.775, p < 0.001; Ward: r = –0.567, p < 0.001). Serum zinc also correlated negatively with total leukocyte and platelet counts in the ward, implying that zinc insufficiency may drive heightened systemic inflammation. Since CRP is a well-validated acute-phase reactant, its elevation in zinc-deficient patients underscores zinc’s role in attenuating oxidative stress and modulating inflammatory responses.(22–24)

Patients exhibited a stepwise decline in serum zinc as sepsis severity and SOFA scores increased—measured at 82.79 ± 10.29 mg/dl in non-septic cases, 70.02 ± 10.18 mg/dl in sepsis, 49.81 ± 6.53 mg/dl in severe sepsis, and 41.71 ± 4.40 mg/dl in septic shock—highlighting zinc’s involvement in immune dysregulation during critical illness. This pattern mirrors prior pediatric research demonstrating that serum zinc concentrations parallel escalating sepsis severity and the extent of organ dysfunction. (4,18,25,26)

Receiver operating characteristic analysis further affirmed the prognostic value of serum zinc. A threshold of ≤88.9 mg/dL achieved 100 % sensitivity and 92.5 % specificity for severe pneumonia, demonstrating excellent discrimination of high-risk cases. These results align with Saleh et al. (2018), who identified a comparable zinc cut-off for predicting pneumonia severity, thereby reinforcing its validity as a biomarker. (18)

Our findings also revealed that PICU patients requiring MV and inotropic support exhibited significantly lower zinc levels. echoing previous studies that associate zinc deficiency and the need for advanced life support measures, possibly due to zinc's role in cellular repair and epithelial barrier function during severe infections. (18,20,25,27,28)

Additionally, both PICU and ward cohorts exhibited an inverse relationship between serum zinc concentrations and hospitalization duration: patients with prolonged inpatient stays had significantly lower zinc levels. This parallels the observations of Kumar and Prakash (2020), who reported extended recovery periods in zinc-deficient children suffering from respiratory infections. (28)

The PRISM III score, a well-established metric for predicting mortality risk in pediatric intensive care units, showed an inverse correlation with serum zinc levels in our study. This finding aligns with previous research from Egypt and China, further supporting the association between lower zinc levels and increased risk of mortality in critically ill children. (18,29)

A meta-analysis, along with numerous individual studies, consistently demonstrated higher serum zinc levels in survivors compared to non-survivors in critical illness. These findings further corroborate our results, reinforcing the prognostic significance of zinc in pediatric pneumonia and its potential role in improving clinical outcomes. (18,20,28,30)

ROC curve analysis in our study identified a serum zinc cut-off of ≤68.44 mg/dL as a strong predictor of PICU mortality, with an area under the curve (AUC) of 0.793, demonstrating substantial discriminative power. This threshold surpasses the previously reported cut-off of 36.6 mg/dL, suggesting that higher zinc levels may still hold prognostic value in predicting survival outcomes among critically ill pediatric patients. (18)

 Conclusion

This study underscores a significant inverse correlation between admission-day serum zinc levels and pneumonia severity, mortality risk, and length of hospital stay. The results reinforce the pivotal role of zinc deficiency in the pathogenesis of severe pneumonia and highlight its potential utility as a biomarker for assessing disease severity and predicting clinical outcomes in pediatric populations.

Competing interests

        No financial or non-financial benefits have been received or will be accepted by any organization directly or indirectly related to the subject of this article.