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Hypocalcemia (Low Level of Calcium in the Blood)

by James L. Lewis, III, MD

In hypocalcemia, the calcium level in blood is too low.

  • A low calcium level may result from a problem with the parathyroid glands, as well as from diet, kidney disorders, or certain drugs.

  • As hypocalcemia progresses, muscle cramps are common, and people may become confused, depressed, and forgetful and have tingling in their lips, fingers, and feet as well as stiff, achy muscles.

  • Usually, the disorder is detected by routine blood tests.

  • Calcium and vitamin D supplements may be used.

Although most of the body's calcium is stored in bones, some circulates in the blood (see Overview of Calcium). About 40% of the calcium in blood is attached (bound) to proteins in blood, mainly albumin. Protein-bound calcium acts as a reserve but has no active function in the body. Only unbound calcium affects the body’s functions. Thus, hypocalcemia causes problems only when the level of unbound calcium is low. Unbound calcium has an electrical (ionic) charge, so it is called ionized calcium.

Causes

Hypocalcemia most commonly results when too much calcium is lost in urine or when not enough calcium is moved from bones into the blood. Causes of hypocalcemia include the following:

  • A low level of parathyroid hormone (hypoparathyroidism), as can occur when the parathyroid glands are damaged during thyroid gland surgery

  • Lack of response to a normal level of parathyroid hormone (pseudohypoparathyroidism)

  • No parathyroid glands at birth

  • A low level of magnesium (hypomagnesemia), which reduces the activity of parathyroid hormone

  • Vitamin D deficiency (due to inadequate consumption or inadequate exposure to sunlight)

  • Kidney dysfunction (a common cause), which results in more calcium excreted in urine and makes the kidneys less able to activate vitamin D

  • Inadequate consumption of calcium

  • Disorders that decrease calcium absorption

  • Pancreatitis

  • Certain drugs, including rifampin (an antibiotic), anticonvulsants (such as phenytoin and phenobarbital), bisphosphonates (such as alendronate, ibandronate, risedronate, and zoledronic acid), calcitonin, chloroquine, corticosteroids, and plicamycin

Symptoms

The calcium level in blood can be moderately low without causing any symptoms. If levels of calcium are low for long periods, people may develop dry scaly skin, brittle nails, and coarse hair. Muscle cramps involving the back and legs are common. Over time, hypocalcemia can affect the brain and cause neurologic or psychologic symptoms, such as confusion, memory loss, delirium, depression, and hallucinations. These symptoms disappear if the calcium level is restored.

An extremely low calcium level may cause tingling (often in the lips, tongue, fingers, and feet), muscle aches, spasms of the muscles in the throat (leading to difficulty breathing), stiffening and spasms of muscles (tetany), seizures, and abnormal heart rhythms.

Diagnosis

Hypocalcemia is often detected by routine blood tests before symptoms become obvious. Doctors measure the total calcium level (which includes calcium bound to albumin) and the albumin level in blood to determine whether the level of unbound calcium is low.

Blood tests are done to evaluate kidney function and to measure magnesium, phosphate, parathyroid hormone, and vitamin D levels. Other substances in blood may be measured to help determine the cause.

Treatment

Calcium supplements, given by mouth, are often all that is needed to treat hypocalcemia. If a cause is identified, treating the disorder causing hypocalcemia or changing drugs may restore the calcium level.

Once symptoms appear, calcium is usually given intravenously. Taking vitamin D supplements helps increase the absorption of calcium from the digestive tract.

Drugs Mentioned In This Article

  • Generic Name
    Select Brand Names
  • ARALEN
  • No US brand name
  • RIFADIN, RIMACTANE
  • BONIVA
  • FOSAMAX
  • ACTONEL
  • DILANTIN
  • MIACALCIN