How should I treat hypocalcemia in an adult, differentiating symptomatic cases (muscle cramps, tetany, seizures, ECG changes, serum calcium <7.0 mg/dL) from asymptomatic or chronic mild cases?

Treatment of Hypocalcemia

For acute symptomatic hypocalcemia (tetany, seizures, cardiac arrhythmias, or calcium <7.0 mg/dL), immediately administer intravenous calcium chloride 10% solution 10 mL (270 mg elemental calcium) over 2-5 minutes with continuous ECG monitoring, while for asymptomatic or chronic mild hypocalcemia, start oral calcium carbonate 1-2 g three times daily plus vitamin D supplementation, keeping total elemental calcium intake below 2,000 mg/day. 1, 2

Immediate Assessment and Stabilization

Before administering any calcium, check and correct magnesium first—hypocalcemia cannot be adequately corrected without addressing concurrent hypomagnesemia, which is present in 28% of hypocalcemic patients. 1 If hypomagnesemia is present, administer magnesium sulfate 1-2 g IV bolus immediately, followed by calcium replacement. 1

Obtain essential labs immediately: pH-corrected ionized calcium (most accurate), serum albumin, parathyroid hormone (PTH), magnesium, phosphate, creatinine, and 25-hydroxyvitamin D. 3, 4 Perform a 12-lead ECG to assess for QT prolongation (>500 ms indicates high risk for torsades de pointes). 3, 1

Acute Symptomatic Hypocalcemia Management

Severity Classification

• Severe (corrected calcium <7.0 mg/dL or ionized calcium <0.75 mmol/L): Causes tetany, seizures, laryngospasm, cardiac arrhythmias, altered mental status—requires immediate IV calcium 3
• Moderate (corrected calcium 7.0-8.0 mg/dL): Produces Chvostek's/Trousseau's signs, muscle cramps, paresthesias 3
• Mild (corrected calcium 8.0-8.4 mg/dL): May be asymptomatic or cause only fatigue and mild paresthesias 3

Intravenous Calcium Administration

Calcium chloride is strongly preferred over calcium gluconate because it delivers 3 times more elemental calcium per volume (10 mL of 10% calcium chloride contains 270 mg elemental calcium vs. only 90 mg in calcium gluconate). 1, 2

Dosing:

• Adults: Calcium chloride 10% solution 10 mL (270 mg elemental calcium) IV over 2-5 minutes 1, 2
• Pediatrics: 2.7-5.0 mg/kg hydrated calcium chloride (0.027-0.05 mL/kg of 10% solution) 2
• Administer via central or deep vein when possible to avoid tissue necrosis if extravasation occurs 1, 2

Critical monitoring during IV administration:

• Continuous ECG monitoring is mandatory to detect arrhythmias 1, 4
• Measure ionized calcium every 4-6 hours during intermittent infusions, every 1-4 hours during continuous infusion 1, 4
• Never administer calcium through the same IV line as sodium bicarbonate or phosphate-containing fluids (precipitation will occur) 1, 5
• Administer slowly—not to exceed 1 mL/min—to avoid hypotension, bradycardia, and cardiac arrest 1, 2

Special Clinical Scenarios

Massive transfusion/trauma patients: Each unit of blood products contains approximately 3 g of citrate that chelates calcium. Monitor ionized calcium continuously and provide ongoing calcium replacement. Citrate metabolism is impaired by hypoperfusion, hypothermia, and hepatic insufficiency. 3, 1

Tumor lysis syndrome with elevated phosphate: Use extreme caution with calcium replacement when phosphate is elevated due to risk of calcium-phosphate precipitation in tissues and kidneys. Administer calcium gluconate 50-100 mg/kg IV slowly only if symptomatic. 1

Seizures from hypocalcemia: Administer IV calcium immediately without waiting for laboratory confirmation if hypocalcemia is suspected. 4

Transition to Oral Maintenance Therapy

Once acute symptoms resolve, transition to oral regimen:

• Calcium carbonate 1-2 g three times daily (preferred due to 40% elemental calcium content and low cost) 3, 1
• Divide doses throughout the day with meals to optimize absorption 3
• Limit individual doses to 500 mg elemental calcium 3
• Total elemental calcium intake must not exceed 2,000 mg/day from all sources (dietary + supplements) 3, 1

Vitamin D Supplementation Strategy

For Vitamin D Deficiency (25-OH vitamin D <30 ng/mL):

• Ergocalciferol (vitamin D2) 50,000 IU orally once monthly for 6 months 1
• Cholecalciferol (vitamin D3) 400-800 IU daily for maintenance 3, 1

For Hypoparathyroidism or Refractory Cases:

• Calcitriol 0.5-2 mcg daily (or 20-30 ng/kg body weight daily) 3, 1
• Alfacalcidol 30-50 ng/kg body weight daily (alternative) 3
• These active vitamin D metabolites should be used under endocrinologist guidance 3

Chronic Hypocalcemia Management

Target Calcium Levels

Maintain corrected total calcium in the low-normal range (8.4-9.5 mg/dL or 2.10-2.37 mmol/L) to minimize hypercalciuria and prevent nephrocalcinosis while avoiding symptoms. 3, 1

Monitoring Requirements

• Measure corrected total calcium and phosphorus at least every 3 months 3, 1
• Monitor pH-corrected ionized calcium, magnesium, PTH, and creatinine regularly 3, 1
• Keep calcium-phosphorus product <55 mg²/dL² to prevent vascular calcification 3
• Monitor urinary calcium excretion to detect hypercalciuria 1
• Annual thyroid function testing in high-risk populations (25% of patients with 22q11.2 deletion syndrome develop hypothyroidism) 1

Special Population Considerations

Chronic kidney disease (CKD) patients:

• Treat when corrected calcium <8.4 mg/dL AND intact PTH is above target range for CKD stage 3, 1
• Elemental calcium from phosphate binders should not exceed 1,500 mg/day 1
• Do NOT use calcium-based phosphate binders when corrected calcium >10.2 mg/dL or PTH <150 pg/mL 1
• The 2025 KDIGO Controversies Conference shifted away from "permissive hypocalcemia" because severe hypocalcemia occurs in 7-9% of patients on calcimimetics, causing muscle spasms, paresthesia, and myalgia 1

Patients with 22q11.2 deletion syndrome:

• 80% lifetime prevalence of hypocalcemia due to hypoparathyroidism 3, 1
• Daily calcium and vitamin D supplementation recommended for all adults 3, 1
• Heightened surveillance during biological stress (surgery, childbirth, infection, fractures) 3, 1
• Avoid alcohol and carbonated beverages (especially colas) which worsen hypocalcemia 3, 1

Patients on bisphosphonates or denosumab:

• Require calcium 600 mg/day and vitamin D3 400 IU/day supplementation to prevent severe hypocalcemia 3, 1

Critical Pitfalls to Avoid

• Never attempt to correct hypocalcemia without first checking and correcting magnesium—this is futile and delays effective treatment 1, 4
• Avoid overcorrection: Iatrogenic hypercalcemia causes renal calculi, nephrocalcinosis, and renal failure 3, 1
• Never mix calcium with sodium bicarbonate or phosphate-containing solutions (precipitation occurs) 1, 5
• Do not use calcium gluconate in tumor lysis syndrome with elevated phosphate except for life-threatening hyperkalemia-induced arrhythmias 1
• Calcium administration can transiently lower serum potassium through transcellular shifts—monitor and correct concurrently 1
• In patients on cardiac glycosides, calcium administration can cause synergistic arrhythmias—give slowly in small amounts with close ECG monitoring 5
• Extravasation causes severe tissue necrosis—if it occurs, immediately discontinue infusion at that site 1, 5

Algorithm for ECG Changes and Arrhythmia Prevention

1. Obtain baseline 12-lead ECG before treatment in all known hypocalcemic patients 1
2. Document QTc interval before and every 8-12 hours after calcium replacement 1
3. If QTc >500 ms or QTc prolongation >60 ms above baseline: Immediately correct hypocalcemia, hypokalemia, and hypomagnesemia concurrently 1
4. Maintain potassium 4.5-5.0 mmol/L (supratherapeutic range) when QT prolongation is present 1
5. Administer IV magnesium 1-2 g MgSO4 bolus as first-line therapy for torsades de pointes, regardless of serum magnesium level 1
6. Discontinue all non-essential QT-prolonging drugs during treatment 1
7. Consider temporary transvenous pacing at rates >70 bpm if torsades persists despite electrolyte correction 1