Association of major metal elements and their ratios in whole blood with risk of recurrent pneumonia in children younger than 36 months: a hospital-based case-control study

Objective To study the association between the concentration of calcium, iron, zinc, copper, and magnesium and their ratios in whole blood and the risk of recurrent pneumonia in infants and young children, and to provide guidelines for the prevention and control of recurrent pneumonia in the population.

Methods A case-control study was conducted among 86 children (< 36 months of age) with recurrent pneumonia who were hospitalized between September 2018 and February 2019, and 174 age-matched healthy children who underwent physical examinations during the same period at Tongshan County People's Hospital in Hubei province. Relevant information on the participants was obtained from the hospital's electronic medical records, and venous blood samples were collected to measure the concentrations of the five metal elements and their ratios. Multivariate logistic regression analysis was used to assess risk factors for recurrent pneumonia in infants and young children; and receiver operating cure (ROC) analysis was used to determine the significance of ratios of mental elements in predicting recurrent pneumonia.

Results The cases had a lower calcium concentration than the controls (1.59 ± 0.22 vs. 1.66 ± 0.17 mmol/L), with a deficiency rate of 22.09%, but a higher copper concentration (17.62 ± 6.18 vs. 14.11 ± 2.97 μmol/L) and a higher magnesium/calcium ratio (0.95 ± 0.14 vs. 0.90 ± 0.12) and copper/zinc ratio (0.25 ± 0.07 vs. 0.20 ± 0.04). Multivariate logistic regression analysis showed that low blood calcium (odds ratio OR = 0.120, 95% confidence interval CI : 0.027 to 0.530), high blood copper (OR = 1.209, 95%CI: 1.127 to 1.298), high magnesium/calcium ratio (OR = 1.039, 95%CI: 1.015 to 1.063), and high copper/zinc ratio (OR = 1.216, 95%CI: 1.137 to 1.301) were associated with an increased risk of recurrent pneumonia in infants and young children. ROC curve analysis showed that the area under the curve (AUC) of magnesium/calcium ratio, copper/zinc ratio, and their combination in predicting recurrent pneumonia in infants were 0.608, 0.707, and 0.758, respectively (P < 0.05 for all).

Conclusion The children less than 36 months of age with recurrent pneumonia have reduced whole blood calcium but increased calcium deficiency rate, copper concentration, magnesium/calcium ratio, and copper/zinc ratio, and magnesium/calcium and copper/zinc ratios could predict the risk of recurrent pneumonia in the children to some extent.