Calcium deficiency

Hypocalcaemia

In medicine, hypocalcaemia (or hypocalcemia) is the presence of low serum calcium levels in the blood, usually taken as less than 2.1 mmol/L or 9 mg/dl or an ionized calcium level of less than 1.1 mmol/L or 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. In the setting of low serum albumin (frequently seen in patients with chronic diseases, hepatic disease or even long term hospitalization), the formula for corrected calcium is: Corrected calcium (mg/dL) = measured total Ca (mg/dL) + 0.8 (4.0 - serum albumin [g/dL]), where 4.0 represents the average albumin level in g/dL; in SI units: Corrected calcium (mmol/L) = measured total Ca (mmol/L) + 0.02 (40 - serum albumin [g/L]), where 40 represents the average albumin level in g/L. Thus, if the albumin is low, the measured calcium may appear low when in fact it is physiologically within normal limits.

Cause

It manifests as a symptom of a parathyroid hormone [PTH] deficiency/malfunction, a Vitamin D deficiency, or unusually high magnesium levels (hypermagnesaemia), or low magnesium levels (hypomagnesaemia).
More specifically, hypocalcaemia may be associated with low PTH levels as seen in hereditary hypoparathyroidism, acquired hypoparathyroidism (surgical removal MCC of hypoparathyroidism), and hypomagnesaemia. Hypocalcaemia may be associated with high PTH levels when the parathyroid hormone is ineffective; in chronic renal failure, the hydroxylation of vitamin D is ineffective, calcium levels in the blood fall, and high PTH levels are produced in response to the low calcium, but fail to return calcium levels to normal.

• Eating disorders
• Exposure to mercury, including infantile acrodynia
• Excessive dietary magnesium, as with supplementation.
• Prolonged use of medications/laxatives containing magnesium
• Chelation Therapy for metal exposure, particularly EDTA
• Absent parathyroid hormone (PTH)
  • Hereditary hypoparathyroidism
  • Acquired hypoparathyroidism
  • Hypomagnesaemia
  • 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
  • In DiGeorge Syndrome, a disease characterized by the failure of the third and fourth pharyngeal pouches to develop, the parathyroid glands do not form and there is thus a lack of PTH.
• 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 hyperphosphataemia
    • Tumour lysis syndrome
    • Acute renal failure
    • Rhabdomyolysis (initial stage)
• Exposure to hydrofluoric acid
• As a complication of pancreatitis
• As a result of hyperventilation
• Alkalosis, often caused by hyperventilation
• Neonatal hypocalcaemia
  • Very low birth weight (less than 1500 grams)
  • Gestational age less than 32 weeks

Symptoms

The neuromuscular symptoms of hypocalcemia are caused by a positive bathmotropic effect due to the decreased interaction of calcium with sodium channels. Since calcium blocks sodium channels and inhibits depolarization of nerve and muscle fibers, diminished calcium lowers the threshold for depolarization.^[1] The symptoms can be recalled by the mnemonic "CATS go numb"- Convulsions, Arrhythmias, Tetany and numbness/parasthesias in hands, feet, around mouth and lips.

• Petechiae which appear as on-off spots, then later become confluent, and appear as purpura (larger bruised areas, usually in dependent regions of the body).
• Oral, perioral and acral paresthesias, tingling or 'pins and needles' sensation in and around the mouth and lips, and in the extremities of the hands and feet. This is often the earliest symptom of hypocalcaemia.
• Carpopedal and generalized tetany (unrelieved and strong contractions of the hands, and in the large muscles of the rest of the body) 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)^[2]
• Tendon reflexes are hyperactive
• Life threatening complications
  • Laryngospasm
  • Cardiac arrhythmias
• ECG changes include:
  • Intermittent QT prolongation, or intermittent prolongation of the QTc (corrected QT interval) on the EKG (electrocardiogram) is noted. The implications of intermittent QTc prolongation predisposes to life-threatening cardiac electrical instability (and this is therefore a more critical condition than constant QTc prolongation). This type of electrical instability puts the patient at high risk of torsades de pointes, a specific type of ventricular fibrillation which appears on an EKG (or ECG) as something which looks a bit like a sine wave with a regularly increasing and decreasing amplitude. (Torsades de pointes, as with any type of ventricular tachycardia, causes death, unless the patient can be electrically cardioverted, and returned to a normal cardiac rhythm.)