Hypocalcemia
Hypocalcemia is a low serum calcium concentration, most often from insufficient parathyroid hormone action (postsurgical or autoimmune hypoparathyroidism, hypomagnesemia, or PTH resistance) or from vitamin D deficiency and chronic kidney disease. Severe or symptomatic disease requires urgent intravenous calcium, while chronic disease is managed with oral calcium, vitamin D repletion, and calcitriol when PTH is absent or the kidney cannot activate vitamin D.
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What this article covers
- Overview
Definition: hypocalcemia is a serum calcium concentration below the normal range, from insufficient parathyroid hormone (PTH) secretion or action, insufficient vitamin D, or a process that consumes…
- Epidemiology
Outpatient screening detection: most hypocalcemic disorders are identified incidentally on a metabolic panel and are mild, with calcium 7.5 to 8.9 mg/dL (1.9 to 2.2 mmol/L).
- Risk factors
Recent anterior neck surgery: thyroidectomy, parathyroidectomy, or radical neck dissection risking direct injury or devascularization of the parathyroid glands.
- Pathophysiology
PTH normally defends serum calcium: it mobilizes bone calcium, increases renal calcium reabsorption, and stimulates renal 1-alpha-hydroxylase to generate active vitamin D; loss of any step in this axis lowers calcium.
- Clinical features
Most patients are asymptomatic or mildly symptomatic: intermittent paresthesia of the hands and feet or perioral numbness is the most common presentation.
- Differential diagnosis
Hypoparathyroidism (postsurgical, autoimmune, infiltrative, congenital): low or inappropriately normal PTH, unlike the elevated PTH of PTH resistance or secondary causes.
- Diagnosis
Establish severity by the corrected calcium level, not a formal criteria set: mild hypocalcemia is 7.5 to 8.9 mg/dL (1.9 to 2.2 mmol/L) and typically asymptomatic; severe hypocalcemia is below 7.5…
- Management
First, for severe hypocalcemia (calcium below 7.5 mg/dL [1.9 mmol/L]) or any symptomatic patient (tetany, laryngospasm, seizure, QT prolongation), give IV calcium and correct magnesium concurrently…
- Complications
Sudden cardiac death: from QT interval prolongation and myocardial dysfunction in severe, untreated hypocalcemia.
- Prognosis
Excellent with prompt treatment of severe disease: IV calcium rapidly reverses acute neuromuscular and cardiac manifestations.
- Prevention
Correct vitamin D deficiency before starting an antiresorptive drug: check 25-hydroxyvitamin D and treat any level below 20 ng/mL (50 nmol/L) before intravenous bisphosphonate or denosumab therapy…
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Related articles
- Hypoparathyroidism
Hypoparathyroidism is PTH deficiency causing hypocalcemia and hyperphosphatemia, most often from inadvertent parathyroid injury during anterior neck surgery. First-line treatment is oral calcium plus calcitriol titrated to a low-normal serum calcium, with recombinant PTH reserved for inadequate control.
- Pseudohypoparathyroidism
Pseudohypoparathyroidism is a rare genetic cause of hypocalcemia from end-organ (kidney and bone) resistance to parathyroid hormone, most often from a maternally inherited inactivating GNAS mutation that produces the Albright hereditary osteodystrophy phenotype alongside hypocalcemia, hyperphosphatemia, and an elevated, not low, PTH level. Acute symptomatic hypocalcemia is treated with intravenous calcium, and chronic disease is managed with oral calcium and calcitriol.
- Familial hypocalciuric hypercalcemia
Familial hypocalciuric hypercalcemia is an autosomal dominant, lifelong, asymptomatic hypercalcemia caused by an inactivating mutation of the calcium-sensing receptor, which raises the parathyroid hormone and renal calcium reabsorption set point. The clinching test is a 24-hour urine calcium-creatinine clearance ratio below 0.01, and management is reassurance and family screening, since parathyroidectomy does not correct the calcium and is not indicated.