EFFECT OF PHOTOTHERAPY ON SERUM ELECTROLYTES IN NEONATES ≥35 WEEKS OF GESTATION WITH HYPERBILIRUBINEMIA

Abstract

Background: Neonatal hyperbilirubinemia is common (≈60% of term and 85% of preterm infants) and can lead to neurotoxicity or kernicterus if untreated. Phototherapy is the standard, effective treatment that converts unconjugated bilirubin into water-soluble isomers for excretion. However, phototherapy has been associated with electrolyte disturbances (hypocalcemia, hyponatremia, hyperkalemia) in some infants. We evaluated changes in serum sodium, potassium, calcium (ionized and total) and magnesium in neonates (≥35 weeks gestation) undergoing phototherapy. Materials and Methods: We conducted a prospective observational study of 86 neonates ≥35 weeks gestation with unconjugated hyperbilirubinemia requiring phototherapy. Subjects were managed per AAP guidelines. Venous blood samples were obtained before phototherapy and after 48 hours. Serum sodium, potassium, total and ionized calcium, magnesium and total bilirubin were measured. Continuous variables are reported as mean ± SD. Paired t-tests compared pre- and post-therapy values; p<0.05 was considered significant. Results: The cohort included 86 neonates (55.8% female) with mean age ≈5 days and mean birth weight ~2.72 kg. Table 1 shows that 34.9% were late-preterm (35–36+6 wk), 44.2% early-term, and 20.9% full-term; 24.4% were low birth weight (<2500 g). All had normal baseline electrolytes (Table 2). After 48 hours of phototherapy, mean total bilirubin fell significantly (14.95 ± 2.41 to 8.86 ± 2.03 mg/dL, p<0.0001). Serum sodium also declined significantly (139.36 ± 3.73 to 137.85 ± 3.91 mEq/L, p<0.0001), whereas changes in potassium (5.02 ± 0.80 to 4.98 ± 0.82 mEq/L, p=0.312), ionized calcium (1.10 ± 0.10 to 1.09 ± 0.10 mmol/L, p=0.689), total calcium (9.12 ± 0.48 to 9.10 ± 0.47 mg/dL, p=0.682) and magnesium (2.01 ± 0.65 to 1.99 ± 0.66 mEq/L, p=0.345) were not significant (Table 2). No neonate developed symptomatic hypocalcemia or severe hyponatremia. Subgroup analysis showed a greater mean sodium drop in low-birth-weight infants (–3.15 vs –1.02 mEq/L; p=0.016), but sex, gestational age and phototherapy type had no significant effects. Conclusion: In this cohort of term neonates, phototherapy significantly lowered serum sodium but had minimal effects on potassium and calcium levels. These findings align with previous reports that phototherapy can cause mild hyponatremia and electrolyte shifts. We recommend routine monitoring of electrolytes during prolonged phototherapy, especially in high-risk or low-birth-weight infants.