Contents
Causes
Hypocalcaemia is an reduction of the corrected blood calcium below the upper limit of the normal range. This usually means a corrected calcium that is less than 2.1mM. There are various causes of hypocalcaemia.
- Hypoparathyroidism
- Dietary deficiency
- Chronic renal failure
- Vitamin D deficiency (either dietary or inadequate sunlight exposure)
- Vitamin D malabsorption
- Vitamin D resistance
- Pseudohypoparathyroidism
- Loop diuretics
- Di George syndrome
- Parathyroidectomy
- Acute pancreatitis
- Phenytoin
- Hypomagnesaemia
- Severe acute hyperphosphataemia
- Alkalosis
Activation of vitamin D occurs in the kidney. This activation becomes deficient in chronic renal failure.
Vitamin D is a fat soluble vitamin (along with vitamins A, E and K). Its asborption is particularly prone to problems in chronic pancreatitis or prolonged obstructive jaundice, both of which compromise the absorption of fats.
Di George syndrome is a rare congenital abnormality in which the parathyroid glands and thymus fail to form.
Acute pancreatitis can be associated with considerable intrabdominal necrosis and calcium can be deposited in the necrotic tissue, thereby drawing it out of the blood. Curiously, hypercalcaemia can precipitate acute pancreatitis.
Magnesium is required for the release of parathyroid hormone.
Clinical Features
Many of the features of hypocalcaemia relate to its role in the function of electrically excitable tissues (skeletal muscle, cardiac muscle and nerves).
Cardiac arrhythmias can develop; the QT interval may be prolonged on the ECG.
Paraesthesia (pins and needles; numbness and tingling) is an early sign and tends to affect the fingers and the perioral area.
Skeletal muscle becomes unstable and prone to prolonged, sustained contraction (tetany); in part this may be due to instability of the nerves that innervate the muscle as much as the muscle fibres themselves. Adequate levels of extracellular divalent cations are necessary to stabilise the transmembrane potential of excitable tissues and the burden of this role falls upon calcium. Chvostek's sign is a form of tetany that affects the facial muscles and is triggered by tapping the cheek. Trousseau's sign is spasm of the muscles of the hand, which draws the hand into a clawed, clenched posture, that is precipitated by leaving an inflated blood pressure cuff on the arm for no more than a few minutes. Muscle spasms can also affect the larynx and produce stridor.
Patients may be irritable, depressed or psychotic. Convulsions can occur.
Investigations
If hypocalcaemia is suspected it can be confirmed by a blood test. An ECG is vital to determine if the heart is showing electrical instability.
Other investigations relate to finding the cause. The level of parathyroid hormone in the blood can be measured. In almost all causes of hypocalcaemia the concentration of parathyroid hormone will be elevated because the hypocalcaemia stimulates the parathyroid glands to release parathyroid hormone; parathyroid hormone levels will be low in hypoparathyroidism because the parathyroid glands have failed and in hypomagnesaemia because the parathyroid glands are unable to respond.
Vitamin D levels can be determined.
Treatment
The main thrust of the treatment is to correct the underlying cause where possible. Calcium supplements can be employed to return calcium levels to normal, aided by activated vitamin D. If rapid correction of hypocalcaemia is necessary, the initial dose of calcium can be given intravenously.