Hypocalcaemia

In medicine, hypocalcemia is the presence of low serum calcium levels in the blood, usually taken as less than 3.5 mmol/L or 9 mg/dl or an ionized calcium level of less than 1.1 mmol/L (4.5 mg/dL). It is a type of electrolyte disturbance. In the blood, about half of all calcium is bound to proteins such as serum albumin, but it is the unbound, or ionized, calcium that the body regulates. If a person has abnormal levels of blood proteins then the plasma calcium may be inaccurate. The ionized calcium level is considered more clinically accurate in this case.

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Cause

It mainly occurs due to a deficiency of parathyroid hormone, inefficient parathyroid hormone, or deficiency of Vitamin D. It may be seen alongside hypomagnesemia.

More specifically, causes include:

• Eating disorders
• Absent parathyroid hormone (PTH)
  • Hereditary hypoparathyroidism
  • Acquired hypoparathyroidism
  • Hypomagnesemia
  • Following parathyroidectomy, "Hungry Bone Syndrome"
  • Following thyroidectomy, the parathyroid glands are located very close to the thyroid and are easily injured or even accidentally removed during thyroidectomy
• Ineffective PTH
  • Chronic renal failure
  • Absent active vitamin D
    • Decreased dietary intake
    • Decreased sun exposure
    • Defective Vitamin D metabolism
      • Anticonvulsant therapy
      • Vitamin-D dependent rickets, type I
  • Ineffective active vitamin D
    • Intestinal malabsorption
    • Vitamin-D dependent rickets, type II
  • Pseudohypoparathyroidism
• Deficient PTH
  • Severe acute hyperphosphatemia
    • Tumor lysis syndrome
    • Acute renal failure
    • Rhabdomyolysis (initial stage)
  • Osteitis fibrosa following parathyroidectomy
• Exposure to hydrofluoric acid
• As a complication of pancreatitis

Symptoms

• Perioral tingling and parasthesia, 'pins and needles' sensation over the extremities of hands and feet. This is the earliest symptom of hypocalcemia.
• Tetany, carpopedal spasm are seen.
• Latent tetany
  • Trousseau sign of latent tetany (eliciting carpal spasm by inflating the blood pressure cuff and maintaining the cuff pressure above systolic)
  • Chvostek's sign (tapping of the inferior portion of the zygoma will produce facial spasms)
• Tendon reflexes are hyperactive
• Life threatening complications
  • Laryngospasm
  • Cardiac arrhythmias
• EKG changes
  • Prolonged QTc
• Prolonged ST interval

Management

• Two ampoules of intravenous calcium gluconate 10% is given slowly in a period of 10 minutes, or if the hypocalcemia is severe, calcium chloride is given instead.
• Maintenance doses of both calcium and vitamin-D (often as 1,25-(OH)₂-D₃, i.e. calcitriol)) are often necessary to prevent further decline.

Animals

Farm animals, mainly cows, can suffer hypocalcaemia (or milk fever) after calving. This is due to a large calcium demand and a slow response from the animal in terms of intestinal absorption or bone resorption. If a cow or other animal is affected it will collapse and have muscle spasms. It will eventually enter a coma and can die.

The treatment is an injection of calcium gluconate. It can be prevented in part by avoiding excess calcium, or more commonly, by regulating potassium in the diet before calving.

See also

• Calcium metabolism
• Hypercalcaemia
• Calcium deficiency (plant disorder)
• Hypomagnesemia with secondary hypocalcemia