Version July 2025
ALGORITHM —
IMMEDIATE ACTION —
The degree of hypocalcemia, along with the rate of fall of serum calcium concentration, determines symptoms and urgency of therapy.
Rapidly identify and begin immediate treatment with intravenous (IV) calcium if any of the following are present:
●Severe symptoms of hypocalcemia – Carpopedal spasm, tetany, seizures.
●Complications of hypocalcemia – Heart failure or prolonged QT interval.
●Acute decrease in corrected serum calcium concentration to ≤7.5 mg/dL (≤1.9 mmol/L), which can increase the risk of complications. To correct serum calcium for any abnormality in albumin, use a calcium correction formula, for example: (calculator 1) for mg/dL, (calculator 2) for standard international units.
If possible, obtain repeat calcium (ionized calcium or total calcium corrected for albumin) with concomitant intact parathyroid hormone (PTH) prior to treatment. Treatment should never be delayed if blood for diagnostic studies cannot be collected.
For those with milder symptoms of neuromuscular irritability (paresthesias) and corrected serum calcium concentrations ≥7.5 mg/dL (1.9 mmol/L), initial treatment with oral calcium supplementation is sufficient. If symptoms do not improve with oral supplementation, IV calcium infusion is required. (See "Clinical manifestations of hypocalcemia" and "Treatment of hypocalcemia", section on 'Severe symptomatic and/or acute hypocalcemia'.)
IV calcium is not warranted as initial therapy for asymptomatic hypocalcemia in patients with impaired renal function in whom correction of hyperphosphatemia and of low circulating 1,25-dihydroxyvitamin D are usually the primary goals. (See "Overview of chronic kidney disease-mineral and bone disorder (CKD-MBD)", section on 'Disorders of calcium balance'.)
INITIAL EVALUATION —
Patients not requiring immediate action require a timely evaluation to identify and treat the underlying cause (table 1). (See "Etiology of hypocalcemia in adults" and "Diagnostic approach to hypocalcemia" and "Treatment of hypocalcemia".)
Repeat serum calcium — The first step in the evaluation of hypocalcemia is to repeat the measurement (ionized calcium or total calcium corrected for albumin) to confirm that there is a true decrease in the serum calcium concentration.
●If the diagnosis of hypocalcemia is in doubt, due to hypoalbuminemia, atypical or absent symptoms, multiple myeloma, or a minimally reduced serum calcium concentration, obtain a serum ionized calcium for the repeat measurement.
●If a laboratory known to measure ionized calcium reliably is not available, the total calcium should be repeated and corrected for the presence of hypoalbuminemia (when present), using a calcium correction formula. There are a number of formulas that have been used to correct the total calcium for serum albumin concentrations [(calculator 1) for mg/dL or (calculator 2) for standard international units], but none appear to be universally acceptable when examined for their correlation with ionized calcium.
If available, review previous values for serum calcium.
Measure PTH — If hypocalcemia is confirmed, measure intact PTH concomitantly with another serum calcium (table 2). (See "Diagnostic approach to hypocalcemia", section on 'Laboratory evaluation'.)
●PTH low or inappropriately normal – A serum PTH within the normal reference range in a patient with hypocalcemia is abnormal. A low or inappropriately normal serum PTH concentration in a patient with hypocalcemia is most consistent with hypoparathyroidism. (See "Hypoparathyroidism", section on 'Diagnosis and evaluation'.)
Hypomagnesemia or autosomal dominant hypocalcemia, a rare disorder characterized by an activating mutation in the calcium-sensing receptor gene or its downstream pathway, are alternative diagnoses. (See "Hypoparathyroidism", section on 'Differential diagnosis'.)
Obtain:
•Magnesium
Hypomagnesemia (serum magnesium concentration below 0.8 mEq/L [1 mg/dL or 0.4 mmol/L]) causes hypocalcemia by inducing PTH resistance or deficiency. Hypocalcemia should resolve within minutes or hours after restoration of normal serum magnesium concentrations if hypomagnesemia was the cause of the hypocalcemia. (See "Hypomagnesemia: Evaluation and treatment".)
A few patients with magnesium-responsive hypocalcemia have normal serum magnesium concentrations. These patients are presumed to have tissue magnesium deficiency. Thus, magnesium supplementation may be indicated in patients with unexplained hypocalcemia who are at risk for hypomagnesemia, such as patients with chronic malabsorption or alcoholism, even when serum magnesium concentrations are normal.
●PTH high – A high serum PTH in a patient with hypocalcemia may be secondary to chronic kidney disease, vitamin D deficiency, or pseudohypoparathyroidism (rare). (See "Vitamin D deficiency in adults: Definition, clinical manifestations, and treatment" and "Etiology of hypocalcemia in infants and children", section on 'End-organ resistance to PTH (pseudohypoparathyroidism)'.)
Obtain:
•25-hydroxyvitamin D
•Creatinine
•Phosphate
REFERENCE RANGE —
The normal range for serum calcium is approximately 8.6 to 10.2 mg/dL (2.15 to 2.54 mmol/L). Interpretation of a specific abnormal test result should be based upon the reference range reported with that result.
CITATIONS —
The supporting references for this content are accessible in the linked topics.
