Abstract
Neonatal hypocalcaemia is defined as serum calcium (S-Ca) < 2.0 mmol/L in fullterm newborns and < 1.75 mmol/L in preterm newborns. Neonatal hypocalcaemia is either early onset (<3 days of age) or late onset (>3 days of age). Newborns with hypocalcaemia are often asymptomatic, but may present with hypotonia, apnea, poor feeding, jitteriness, seizures, and cardiac failure. Signs of hypocalcaemia rarely occur unless S-Ca drops below 1.75 mmol/L. Neonatal hypocalcaemia can be a result of hypoparathyroidism (transient or primary), increased serum calcitonin, sepsis, asphyxia, hepatopathy, hypomagnesaemia, high phosphate load, transient hypoparathyroidism, and, rarely, transient neonatal pseudohypoparathyroidism (transient resistance to biological actions of parathyroid hormone [PTH]). We present three boys (two with gestational age 39 weeks, one 36 weeks; none of them with either asphyxia or sepsis) with mild hypotonia, where S-Ca in the range of 1.67-1.9 mmol/L was detected within the first three days of life, together with hyperphosphataemia (serum phosphate [P] 2.5-2.6 mmol/L), normomagnesaemia (serum magnesium [Mg] 0.77-0.88 mmol/L), normal alkaline phosphatase (ALP) activity (2.8-4.5 µkat/L) and high serum PTH (40-51 pg/mL; normal = 5-28). In spite of gradual increase of S-Ca, the elevated serum PTH persisted beyond days 3, 4 and 6 in all three boys, together with normal or low-to-normal S-Ca, high or normal-to-high serum P and no increases in serum ALP. The mothers´ S-Ca, P, Mg, ALP, PTH levels were within normal reference ranges. With regard to laboratory results, the diagnosis of transient neonatal pseudohypoparathyroidism (due to immaturity of PTH-receptors) is highly probable.in these three neonates.

Key words: Calcium; Neonate; Hypocalcaemia; Parathyroid hormone; Pseudohypoparathyroidism