Phototherapy-induced hypocalcemia and hypoparathyroidism in icteric term newborns

Phototherapy is demonstrated to cause hypocalcemia by decreasing melatonin levels and increasing cortisol levels. However, the relationship between parathyroid hormone (PTH) level and calcium has not been previously evaluated in patients receiving phototherapy. Our study aimed to evaluate the effect of phototherapy on ionized calcium (iCa), total calcium (tCa), corrected calcium (cCa), magnesium (Mg), phosphorus (P), 25-hydroxyvitamin D (25(OH)D), and PTH levels.

Infants who were born at term and received inpatient phototherapy for indirect hyperbilirubinemia were included in our study. The patients' gestational age, birth weight, and phototherapy durations were recorded. Total bilirubin, albumin, iCa, tCa, cCa, Mg, 25(OH)D, and PTH levels before and after phototherapy were compared. Laboratory results were also compared between patients who received phototherapy for ≤24 h, 25-47 h, and ≥48 h.

A total of 166 term infants were included in the study. The mean duration of phototherapy was 31.9 ± 9.2 h. Albumin levels before and after phototherapy were similar (p=0.246). However, there were significant decreases in iCa, tCa, cCa, Mg, 25(OH)D, and PTH levels after phototherapy (p<0.001), while P level was significantly increased after phototherapy (p<0.001). In addition, P levels increased with >24 h of phototherapy, while iCa, tCa, cCa, Mg, 25(OH)D, and PTH levels decreased significantly with ≥48 h of phototherapy (p=0.002, p=0.008, p=0.001, p=0.012, and p<0.001, respectively).

This study demonstrates that PTH suppression is one of the causes of phototherapy-induced hypocalcemia.