Hypocalcemia is defined as a total serum calcium concentration of less than 2.1 mmol/L (8.5 mg/dL) in children, less than 2 mmol/L (8 mg/dL) in term neonates, and less than 1.75 mmol/L (7 mg/dL) in preterm neonates.
Hypocalcaemia is one of the commonest disorders of mineral metabolism seen in children and can be a consequence of several different aetiologies. These include a failure of secretion or action of parathyroid hormone, disorders of vitamin D metabolism and abnormal function of the calcium sensing receptor.
Normal Calcium Metabolism
Calcium is the most abundant mineral in the body. Of the body’s total calcium, 99% is in bone, and serum levels constitute less than 1%.Various factors regulate the homeostasis of calcium and maintain serum calcium within a narrow range. These include parathormone (PTH), vitamin D, hepatic and renal function (for conversion of vitamin D to active metabolites), and serum phosphate and magnesium levels.
Although total serum calcium levels are often measured and reported, ionized calcium is the active and physiologically important component.
The concentration of calcium in the serum is critical to many important biologic functions, including the following:
Calcium messenger system by which extracellular messengers regulate cell function
Activation of several cellular enzyme cascades
Smooth muscle and myocardial contraction
Nerve impulse conduction
- Secretory activity of exocrine glands.
Effects of Hypocalcemia on the Bodily Functions
Hypocalcemia manifests as central nervous system (CNS) irritability and poor muscular contractility. Low calcium levels decrease the threshold of excitation of neurons, causing them to have repetitive responses to a single stimulus. Because neuronal excitability occurs in sensory and motor nerves, hypocalcemia produces a wide range of peripheral and CNS effects, including paresthesias, tetany (ie, contraction of hands, arms, feet, larynx, bronchioles), seizures, and even psychiatric changes in children.
Overall, one of the most common causes of hypocalcemia is renal failure, which results in hypocalcemia because of inadequate 1-hydroxylation of 25-hydroxyvitamin D and hyperphosphatemia due to diminished glomerular filtration.
Although hypocalcemia is most commonly observed among neonates, it is frequently reported in older children and adolescents, especially in PICU settings.
Hypocalcemia in a Neonate
In the neonatal age hpocalcemia may be caused by:
Maternal Diabetes mellitus