Hypocalcemia is a fall in calcium in the blood below normal: total calcium < 8.5 mg/dL (2.12 mmol/L) or a reduced ionized calcium. Calcium is needed for the work of nerves, muscles and the heart, so its deficit shows up as increased excitability of tissues.
About 45% of blood calcium is bound to albumin, so with low albumin the measured "total" calcium is understated — the result must be corrected or the ionized calcium looked at.
Causes
The most common cause is a lack of parathyroid hormone (hypoparathyroidism), for example after thyroid surgery. Calcium is also lowered by a deficit of vitamin D (with secondary hyperparathyroidism) and by chronic kidney disease, in which the activation of vitamin D is impaired.
A separate cause is a deficit of magnesium: it disrupts the production and action of parathyroid hormone. Less often hypocalcemia is caused by acute pancreatitis and some medications.
Symptoms
Mild chronic hypocalcemia may not be felt. With a pronounced or rapid fall, numbness and tingling appear around the mouth and in the fingertips, along with muscle spasms and cramps (tetany).
A doctor may check the Chvostek sign (twitching of the facial muscles when tapped) and the Trousseau sign (spasm of the hand when a cuff is inflated). In severe cases, seizures, laryngospasm and heart-rhythm disturbances are possible.
Diagnosis and what to do
Total and ionized calcium, albumin, parathyroid hormone, vitamin D, magnesium, phosphorus and creatinine are measured — this helps find the cause. With low albumin, the corrected or ionized calcium is used.
Treatment depends on the cause: calcium supplements and active forms of vitamin D, correction of a magnesium deficit. Acute severe hypocalcemia is treated in hospital.
Reference ranges
Approximate reference values for blood calcium in adults (laboratories differ):
| Total calcium | 2.12 – 2.62 mmol/L (8.5 – 10.5 mg/dL) |
| Ionized calcium | 1.16 – 1.31 mmol/L |
| Hypocalcemia (total) | < 2.12 mmol/L (< 8.5 mg/dL) |
| Albumin correction | +0.2 mmol/L for every −10 g/L of albumin below 40 g/L |
Calculate using this marker
Calculators where Hypocalcemia is used directly:
Frequently asked questions
Why is calcium "falsely" low when albumin is low?
Almost half of blood calcium is bound to albumin, while the laboratory measures total calcium. With low albumin it is understated, although the active (ionized) calcium may be normal. That is why an albumin correction is used or ionized calcium is measured.
How dangerous is hypocalcemia?
Mild chronic hypocalcemia may not be felt. A pronounced or rapid fall causes numbness, muscle spasms (tetany) and, in severe cases, seizures, laryngospasm and heart-rhythm disturbances, which require emergency care.