Hypocalcæmi

Hypocalcæmi denotes a lower-than-normal level of calcium in the extracellular fluid, most often in serum. Normal total calcium generally ranges from about 8.5 to 10.5 mg/dL, with ionized calcium about 1.12 to 1.32 mmol/L; total calcium can be affected by albumin levels, so measurement of ionized calcium or correction for albumin is sometimes needed.

Causes of hypocalcæmi are diverse. Reduced secretion or action of parathyroid hormone (PTH) is a common cause, as after thyroid or parathyroid surgery or in autoimmune or infiltrative diseases. Vitamin D deficiency or resistance lowers intestinal calcium absorption. Chronic kidney disease impairs calcitriol production and promotes phosphate retention, both contributing to hypocalcæmi. Acute pancreatitis, massive transfusion with citrate, sepsis, and magnesium deficiency can contribute. Drugs such as loop diuretics, bisphosphonates, or certain anticonvulsants may also play a role. Hypoalbuminaemia lowers measured total calcium but not necessarily the ionized fraction; acid–base status can shift calcium binding to albumin.

Clinical features range from asymptomatic to neuromuscular irritability, including perioral numbness, tingling, cramps, tetany, Chvostek sign, and Trousseau phenomenon; seizures may occur. Cardiac effects include prolongation of the QT interval. Symptoms often reflect low ionized calcium rather than total calcium.

Diagnosis involves measurement of total and ionized calcium, with correction for albumin if needed (corrected calcium = measured Ca + 0.8 × [4 − albumin g/dL]). Assessment typically includes magnesium, phosphorus, PTH, vitamin D status, and renal function to identify the underlying cause.

Management depends on severity. Acute symptomatic hypocalcæmi is treated with intravenous calcium, usually calcium gluconate, with cardiac monitoring and gradual conversion to oral calcium as appropriate. Chronic management uses oral calcium supplementation and active vitamin D (calcitriol) or analogs, while addressing underlying causes and correcting magnesium deficiency if present.