Hyponatremia in children with pneumonia rarely means SIADH.

Background: Hyponatremia (HN) < 135 mmol/L is a frequent finding in children with community-acquired pneumonia (CAP). We aimed to determine the proportion of syndrome of inappropriate antidiuretic hormone secretion (SIADH) among patients with CAP and HN. Moreover, we wished to investigate the relationship between HN and inflammatory markers, bacterial etiology and prognosis in hospitalized children with CAP.

Methods: We carried out a prospective, observational, multicentre, prospective cohort study. Eligible participants were children from 1 month to 17 years old hospitalized due to CAP from 2012 to 2015.

Results: A total of 150 children were analyzed. Forty-five (30%) patients had serum sodium levels of less than 135 mmol/L. Patients with HN had significantly higher concentrations of inflammatory biomarkers. They also had significantly lower osmolality and urine sodium. They also had longer hospitalizations and more days of fever. Only 16 out of the 45 (35%) patients with HN had confirmed calculated plasma osmolality (<275 mOsm/kg). Only 5 out of 37 (13%) patients with available measurements of plasma osmolality and urine sodium fulfilled the criteria for SIADH. Among the 16 patients with HN and hypo-osmolality, 15 had a fractional sodium excretion (EFNa) levels of less than 1%. We found a significant inverse linear correlation between serum sodium and C-reactive protein, as well as serum sodium and procalcitonin. We found a significant direct correlation between serum sodium and urine sodium.

Conclusion: HN is a common finding in hospitalized children with CAP. True SIADH is a rare event. HN has a good correlation with inflammatory biomarkers.