Comparison of Serum Electrolytes among Febrile Children with and without Seizures: A Cross-sectional Study

Introduction: Febrile Seizures (FS) are common in early childhood, and bedside biochemical testing is frequently ordered despite mixed evidence regarding underlying biochemical drivers. Clarifying which analytes truly differ at presentation can help streamline acute care, particularly in resource-constrained settings. Aim: To compare serum sodium, magnesium, total calcium, ionised calcium, and 25-hydroxyvitamin D levels between children with febrile seizures (FS) and age-matched children with febrile illness without seizures (FI). A secondary objective was to evaluate these analytes across FS subgroups based on seizure type (simple vs. complex). Materials and Methods: A cross-sectional study was conducted at Max Super Speciality Hospital, Saket, New Delhi, India, from April to November 2016. Children aged six months to five years were enrolled as FS cases (n=64) and febrile illness controls without seizures (FI; n=64). FS cases were included according to the International League Against Epilepsy (ILAE) and American Academy of Paediatrics (AAP) criteria. Serum sodium and total calcium were measured using ion-selective electrodes (indirect potentiometry), magnesium by the calmagite timed endpoint method, ionised calcium by direct potentiometry, and 25-hydroxyvitamin D by chemiluminescent immunoassay. Student’s t-test/ANOVA and χ² tests were used for statistical analysis. Results: The FS and FI groups were comparable with respect to age and sex. Within the FS cohort, 19 children (29.7%) had a prior history of febrile seizures, and 8 (12.5%) reported a positive family history. Forty children (62.5%) presented with complex febrile seizures. Mean±SD analyte values in the FS versus FI groups were as follows: sodium 138.17±5.10 vs. 138.61±4.72 mEq/L (p-value=0.615); magnesium 1.85±0.26 vs. 1.79±0.22 mg/dL (p-value=0.179); total calcium 8.88±0.56 vs. 9.27±0.55 mg/dL (p-value<0.0001); ionised calcium 0.97±0.14 vs. 1.01±0.11 mmol/L (p-value≈0.07); and vitamin D 20.02 ±8.08 vs. 20.43±9.77 ng/mL (p-value=0.792). No meaningful inter-relationships were observed among the five biomarkers. Conclusion: Children with FS had significantly lower total calcium levels and a non significant trend toward lower ionised calcium levels compared with febrile controls, while sodium, magnesium, and vitamin D levels did not differ significantly. In this clinical setting, routine assessment of total and ionised calcium in children with FS appears justified. Vitamin D levels were low in both groups, supporting the need for population-level vitamin D optimisation strategies.