HypocalcemiaHypocalcemia is a laboratory and clinical abnormality that is observed with relative frequency, especially in neonatal pediatric patients.

Definition

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.

Causes

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:

Prematurity

Birth asphyxia

Maternal Diabetes mellitus

Intrauterine growth retardation

One cause of late neonatal hypocalcemia is an exogenous phosphate load; this is most commonly seen in developing countries. The problem results when the neonate is fed with phosphate-rich formula or cow’s milk. Whole cow’s milk has 7 times the phosphate load of breast milk.

Hypocalcemia in Infants and Children

Hypoparathyroidism, abnormal vitamin D production or action, and hyperphosphatemia are among the causes of hypocalcemia in infants and children.

Other causes of hypocalcemia in infants and children include the following:

Malabsorption syndromes

Hungry bone syndrome

Alkalosis- metabolic or respiratory

Pancreatitis

Clinical Signs and Symptoms

In patients with hypocalcemia, the history varies depending on age. In newborns, patient history can include the following:

  • Possibly no symptoms
  • Lethargy
  • Poor feeding
  • Vomiting
  • Abdominal distension

History in children can be as follows:

  • Seizures
  • Twitching
  • Cramping
  • Laryngospasm, a rare initial manifestation.

Children’s symptoms include the following:

  • Lethargy
  • Cyanosis
  • Tremulousness
  • Seizures
  • Apnea
  • Tetany and signs of nerve irritability, such as the Chvostek sign, carpopedal spasm, the Trousseau sign, and stridor.
Investigations
There are several important investigations required in the management of a child with hypocalcaemia, the majority of which are biochemical in nature. It is usually the total plasma calcium that is measured in the blood although some laboratories and near patient testing facilities will measure the ionised calcium which is usually 50% of the total plasma calcium.
The following investigations needs to be done
Plasma albumin
Plasma or serum alkaline phosphatase
Plasma creatinine
Plasma 25-hydroxyvitamin D
Serum parathyroid hormone
Store serum, e.g. for 1,25-dihydroxyvitamin D3
Send blood for DNA studies as appropriate
Urine for calcium/creatinine ratio
X-ray of wrist or knee.
Treatment

Any newborn infant with hypocalcemia should be monitored in the neonatal ICU. (Because most babies with hypocalcemia are preterm, they often have already been admitted there.)

Treatment of asymptomatic patients with hypocalcemia remains controversial, especially with regard to neonates. Some authorities suggest that treating such patients is unnecessary. Most clinicians agree, however, that hypocalcemia should be treated promptly in any symptomatic neonate or older child because of the condition’s serious implications for neuronal and cardiac function. Any child with symptomatic hypocalcemia should be admitted to the hospital .

Oral calcium therapy is used in asymptomatic patients and as follow-up to intravenous (IV) calcium therapy. IV treatment is usually indicated in patients having seizures, those who are critically ill, and those who are planning to have surgery.

Managing Seizures

General medical care in patients with hypocalcemia involves stabilization with management of the patient’s airway and breathing if seizures occur. Anticonvulsants are commonly administered before hypocalcemia is confirmed in a new patient. However, seizures usually do not respond to the usual antiseizure medications until calcium is intravenously administered.

More to consider

Magnesium administration is necessary to correct any hypomagnesemia because hypocalcemia does not respond until the low magnesium level is corrected.

Administration of phosphate-lowering agents may be necessary if hypocalcemia is associated with hyperphosphatemia.

Dietary Advice

A diet high in calcium and low in phosphate is required in most instances. Infants drinking regular cow’s milk or evaporated milk must be given humanized infant formula instead. Patients with renal failure should be given a low-solute, low-phosphate formula.

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