Hypocalcemia is defined as a serum calcium concentration of less than 2.25 mmol/L.
Etiology
Vitamin D Deficiency
This can result from insufficient dietary intake of vitamin D or inadequate sunlight exposure. It can also occur due to impaired intestinal absorption caused by conditions such as obstructive jaundice, chronic diarrhea, or steatorrhea. Additionally, liver cirrhosis or renal failure may lead to defects in vitamin D hydroxylation.
Hypoparathyroidism
This is often observed clinically after unintentional removal of the parathyroid glands during parathyroid or thyroid surgery, leading to parathyroid hormone deficiency. This results in reduced bone resorption and increased bone formation, ultimately causing hypocalcemia.
Chronic Renal Failure
Reduced intestinal calcium absorption can occur in this condition, along with elevated serum phosphate levels, both of which contribute to decreased serum calcium levels.
Acute Pancreatitis
Reduced responsiveness to parathyroid hormone, overproduction of glucagon, and the formation of calcium soaps due to the binding of pancreatic lipase to calcium released from inflamed or necrotic pancreatic tissue can impair calcium absorption.
Clinical Manifestations
Hypocalcemia is associated with increased neuromuscular excitability, presenting with perioral and fingertip numbness and tingling, tetany, hyperactive deep tendon reflexes, and a positive Chvostek's sign. Severe cases can result in laryngospasm, bronchospasm, seizures, or even respiratory arrest. Neuropsychiatric symptoms include irritability, depression, and cognitive impairment.
The cardiovascular effects primarily involve arrhythmias, such as conduction block, which, in severe cases, can lead to ventricular fibrillation or heart failure. The classic electrocardiographic presentation includes significant prolongation of the QT interval and the ST segment. Hypocalcemia can also cause skeletal discomfort, pathological fractures, and skeletal deformities.
Diagnosis
Diagnosis is usually based on the patient's medical history, physical examination, and laboratory testing. A serum calcium concentration below 2.25 mmol/L is indicative of hypocalcemia.
Treatment
When symptoms such as tetany or laryngospasm are present, immediate intervention is necessary. Intravenous administration of 10% calcium gluconate, diluted and injected slowly over a period of time (10–20 ml), typically produces rapid effects. Continuous intravenous infusion of 10% calcium gluconate diluted in 5% glucose solution can be used, with the infusion rate adjusted until serum calcium levels reach the lower limit of the normal range.
For patients with concurrent hypomagnesemia, magnesium supplementation is helpful in resolving hypocalcemia. Chronic hypocalcemia requires treatment of the underlying condition, such as addressing vitamin D deficiency or managing hypoparathyroidism. Combined calcium and vitamin D supplementation is commonly recommended. Calcitriol with calcium carbonate or calcium gluconate is frequently used in clinical practice. The therapeutic goal is to maintain serum calcium levels within the lower limit of the normal range.