Approach to Neonatal Hypocalcemia

Abstract

Hypocalcemia in neonates is defined as total serum calcium concentration less than 7.5-8 mg/dL and/or ionized calcium less than 4.4 mg/dL in neonates (>1500 g) and total serum calcium concentration less than 7 mg/dL or ionized calcium less than 3.6 mg/dL in low-birth-weight neonates (<1500 g). About 80% of the calcium transfer across the placenta occurs in the last trimester. Parathyroid hormone-related peptide (PTHrP) regulates the positive calcium balance in the placenta. Postpartum serum calcium level in neonates depends on an intricate relationship between PTH and renal and skeletal factors. Based on the timing of the presentation, hypocalcemia can be early onset (develops in the first 72 hours of life) and late onset (occurs after 72 hours of life). Causes of early-onset hypocalcemia include prematurity, SGA, IUGR, birth asphyxia, diabetes mellitus, or toxemia in the mother. Late-onset neonatal hypocalcemia may be caused by increased dietary phosphate content, neonatal vitamin D deficiency, hypomagnesemia, hypoparathyroidism, or parathyroid hormone resistance. We present a neonate with hypocalcemia due to transient hypoparathyroidism secondary to maternal adenoma. A thorough history and physical examination are essential to identify at-risk asymptomatic infants who need screening for hypocalcemia. Neonatal hypocalcemia can be a serious event and can cause serious morbidity and mortality. Majority of the early as well as transient late neonatal hypocalcemia resolves completely, while lifelong treatment may be required in some cases depending on the etiology. A 14-day-old male infant was brought to the emergency department with the complaints of worsening seizure-like activity since Day 3 of life. He was born at 39 weeks with a birth weight of 3.09 kg via vaginal delivery to a G3 mother and was sent home on Day 2 of life. Mother noticed shaking of his extremities during sleep on Day 3 of life. These episodes gradually increased in severity and frequency. Mother described these events as diffuse generalized stiffening and shaking, facial grimacing, and gaze abnormalities with cyanosis. There were no constitutional symptoms or sick contacts. Current diet included standard neonatal formula. Maternal history was significant for parathyroid adenoma detected during her second pregnancy. Surgery was deferred as the size of the adenoma reduced after delivery. During her current pregnancy, mother's serum calcium was elevated, with a maximum of up to 12 mg/dL, requiring hydration. Initial laboratory studies revealed hypocalcemia (serum calcium 5.3 mg/dL), hyperphosphatemia (8.2 mg/dL), hypomagnesemia (1.34 mg/dL), low serum 25 hydroxy vitamin D (25OHD) (12.9 ng/ mL), and inappropriately low intact PTH level (19 pg/mL). Other laboratory studies including hematologic, septic, and metabolic workup were normal. The urine calcium creatinine ratio was 0.3 mg/mg.