What is the evaluation and management approach for hypocalcemia (low calcium levels)?

Evaluation and Management of Hypocalcemia

The evaluation of hypocalcemia should begin with measurement of ionized calcium, which is more accurate than total calcium, along with parathyroid hormone (PTH), magnesium, phosphorus, vitamin D levels, and renal function tests to determine the underlying cause. 1

Diagnosis

Laboratory Assessment

• Ionized calcium: Most accurate test for diagnosis (normal range: 1.1-1.3 mmol/L)
• Albumin-corrected total calcium: When ionized calcium is unavailable
  • Formula: Corrected calcium (mg/dL) = Total calcium (mg/dL) + 0.8 × [4 - Serum albumin (g/dL)] 2
• Parathyroid hormone (PTH): Essential for determining etiology
• Magnesium: Hypomagnesemia can cause or worsen hypocalcemia
• Phosphorus: To identify hyperphosphatemia
• 25-hydroxyvitamin D: To assess vitamin D status
• Renal function tests: To evaluate kidney function

Clinical Manifestations

• Neuromuscular: Perioral numbness, carpopedal spasms, tetany, paresthesias
• Cardiac: Prolonged QT interval, arrhythmias
• Other: Fatigue, irritability, abnormal involuntary movements

Management

Acute Symptomatic Hypocalcemia

1. For severe symptoms (tetany, seizures, cardiac arrhythmias):

   • Administer calcium gluconate 50-100 mg/kg IV slowly with ECG monitoring 1
   • Do not exceed infusion rate of 200 mg/minute in adults 1
   • Monitor ionized calcium every 1-4 hours during continuous infusion 3

2. For moderate symptoms:

   • Calcium gluconate 1-2 g IV over 10-20 minutes 3
   • Follow with continuous infusion if needed

Chronic Hypocalcemia

1. Oral calcium supplementation:

   • Elemental calcium 1-2 g/day divided into multiple doses 1
   • Common formulations: calcium carbonate, calcium citrate

2. Vitamin D supplementation:

   • Daily vitamin D supplementation for all patients with hypocalcemia 1
   • Consider calcitriol for severe or refractory cases

Special Considerations

• Chronic kidney disease: Patients with GFR <60 mL/min/1.73 m² are at risk for hypocalcemia 2

  • Target calcium levels: 8.4-9.5 mg/dL, preferably toward lower end 1
  • Monitor calcium, PTH, and phosphate regularly

• Drug interactions:

  • Cardiac glycosides: Risk of synergistic arrhythmias; close ECG monitoring recommended 3
  • Calcium channel blockers: Calcium administration may reduce response 3
  • Ceftriaxone: Contraindicated with calcium in neonates due to risk of fatal precipitates 3

Monitoring

• During intermittent infusions: Measure serum calcium every 4-6 hours 3
• During continuous infusion: Measure serum calcium every 1-4 hours 3
• For chronic management: Regular monitoring of calcium, PTH, magnesium, and renal function 1

Complications and Pitfalls

• Tissue necrosis and calcinosis: Can occur with or without extravasation; immediately discontinue IV administration at affected site if noted 3
• Rapid administration risks: Hypotension, bradycardia, cardiac arrhythmias; always dilute calcium gluconate with 5% dextrose or normal saline and infuse slowly 3
• Aluminum toxicity: Calcium products may contain aluminum (up to 400 mcg per liter) that can be toxic 3
• Hypercalciuria: Can lead to renal dysfunction; maintain serum calcium in low-normal range for patients with hypoparathyroidism 4

Prevention

• Increased monitoring during periods of biological stress (surgery, fracture, infection, childbirth) 1
• Avoid alcohol and cola drinks, which can worsen hypocalcemia 1
• Long-term untreated hypocalcemia increases risk of osteopenia or osteoporosis 1