How should severe hypocalcemia be corrected?

Correcting Hypocalcemia (0.82 mmol/L)

For a calcium level of 0.82 mmol/L (ionized), immediately administer intravenous calcium chloride 10 mL of 10% solution (270 mg elemental calcium) over 2-5 minutes with continuous ECG monitoring, as this represents severe symptomatic hypocalcemia requiring urgent correction. 1

Immediate Assessment & Stabilization

Before administering calcium, you must:

• Check magnesium first – hypomagnesemia is present in 28% of hypocalcemic patients and calcium replacement will fail without correcting magnesium 1. If magnesium <1.0 mg/dL, give magnesium sulfate 1-2 g IV bolus immediately before calcium 1
• Obtain baseline ECG to document QTc interval and monitor for arrhythmias during calcium administration 1
• Verify IV line patency – use a central line when possible because calcium chloride causes severe tissue necrosis if extravasated 1

Acute IV Calcium Replacement

Calcium chloride is strongly preferred over calcium gluconate because 10 mL of 10% calcium chloride delivers 270 mg elemental calcium versus only 90 mg from the same volume of calcium gluconate 1. This 3-fold difference is critical in severe hypocalcemia.

Dosing Protocol

• Initial bolus: Calcium chloride 10 mL of 10% solution IV over 2-5 minutes 1
• Continuous infusion: If ionized calcium remains <0.9 mmol/L after bolus, start calcium gluconate infusion at 1-2 mg elemental calcium/kg/hour, titrating to maintain ionized calcium 1.15-1.36 mmol/L 1
• Monitoring frequency: Measure ionized calcium every 4-6 hours during intermittent infusions and every 1-4 hours during continuous infusion 1, 2

Critical Safety Measures During IV Administration

• Never mix calcium with sodium bicarbonate or phosphate-containing fluids – precipitation will occur 1
• Continuous cardiac monitoring is mandatory to detect QT prolongation and arrhythmias 1
• Hold calcium administration if serum phosphate >5.5 mg/dL – the elevated calcium-phosphorus product markedly increases soft-tissue calcification risk 1

Transition to Oral Therapy

Once the patient is stable and able to take oral medications:

• Calcium carbonate 1-2 g three times daily (providing 1,200-2,400 mg elemental calcium) 1
• Calcitriol 0.5-2 mcg daily if hypoparathyroidism is the cause 1
• Limit total elemental calcium intake to ≤2,000 mg/day from all sources (diet + supplements) to prevent hypercalciuria and nephrocalcinosis 1

Essential Concurrent Interventions

Magnesium Correction

Hypomagnesemia impairs both PTH secretion and end-organ PTH response, making calcium supplementation ineffective 1. If magnesium is low:

• Magnesium sulfate 1-2 g IV bolus for symptomatic patients 1
• Oral magnesium oxide 12-24 mmol daily for chronic supplementation 1

Vitamin D Assessment

• Measure 25-hydroxyvitamin D – if <30 ng/mL, start ergocalciferol 50,000 IU monthly for 6 months 1
• Do not start calcitriol before correcting nutritional vitamin D deficiency – this can precipitate hypercalcemia 1

Target Calcium Levels & Monitoring

• Acute phase target: Ionized calcium 1.15-1.36 mmol/L (corrected total calcium 8.4-9.5 mg/dL) 1
• Chronic management target: Maintain corrected total calcium in the low-normal range (8.4-9.5 mg/dL) to minimize hypercalciuria while preventing symptoms 1
• Monitoring frequency: Check corrected calcium and phosphorus at least every 3 months during chronic supplementation 1

Special Clinical Scenarios

If Patient Has CKD Stage 5

• Target corrected calcium 8.4-9.5 mg/dL (toward the lower end) 1
• Avoid calcium-based phosphate binders if corrected calcium >10.2 mg/dL or PTH <150 pg/mL 1
• Consider adjusting dialysate calcium to 3.0-3.5 mEq/L if additional calcium supply is needed 1

If Phosphate is Elevated (>5.5 mg/dL)

• Do not give calcium until phosphate is reduced below 5.5 mg/dL – the calcium-phosphorus product must stay <55 mg²/dL² 1
• Start non-calcium-containing phosphate binders (sevelamer or lanthanum) first 1
• Only after phosphate control is achieved can you safely administer calcium 1

If Patient is Receiving Massive Transfusion

• Monitor ionized calcium continuously – each unit of blood products contains ~3 g of citrate that binds calcium 1
• Citrate metabolism is impaired by hypoperfusion, hypothermia, and hepatic insufficiency, requiring more aggressive calcium replacement 1

Common Pitfalls to Avoid

• Never use calcium gluconate alone in severe hypocalcemia – it delivers insufficient elemental calcium 1
• Never correct calcium before correcting magnesium – calcium replacement will fail 1
• Never give calcium through the same IV line as bicarbonate – precipitation occurs 1
• Never exceed 2,000 mg/day total elemental calcium – increases risk of vascular calcification and kidney stones 1
• Never start active vitamin D before checking 25-hydroxyvitamin D – may cause hypercalcemia if nutritional deficiency exists 1

Recent Guideline Shift

The 2025 KDIGO Controversies Conference shifted away from "permissive hypocalcemia," particularly in patients on calcimimetics, because severe hypocalcemia occurs in 7-9% of such patients and causes muscle spasms, paresthesia, and myalgia 1. This represents a paradigm shift toward more aggressive correction while carefully monitoring for vascular calcification risk 1.