Hypocalcemia

Diagnosis

Indications for Testing

• Neurologic signs
  • Perioral numbness or other paresthesias
  • Muscle spasms/cramps
  • Neuromuscular irritability
• Thyroid or parathyroid resection or other neck surgery, irradiation to neck
• Chronic kidney disease
• Prolongation of QT interval on electrocardiogram (ECG)
• Malnutrition or malabsorption

Laboratory Testing

• Initial testing
  • Serum calcium and albumin 
    • Corrected calcium = measured total calcium + 0.8 (4.0 - serum albumin)
  • Phosphate
  • Magnesium
  • Creatinine
• If calcium is low, consider repeat testing with ionized calcium
  • Ionized calcium needs no correction for hypoalbuminemia but should be corrected for pH
• If hypocalcemia is confirmed, order intact PTH
  • Elevated PTH, normal or high phosphate, normal magnesium, high creatinine: consider renal failure/pseudohypoparathyroidism
  • Elevated PTH, normal or low phosphate, normal magnesium, normal creatinine: consider vitamin D testing
    • Low vitamin D 25(OH): vitamin D deficiency confirmed
  • Low PTH, normal or high phosphate, normal creatinine, low or normal magnesium: consider hypoparathyroidism or hypomagnesemia
  • Normal PTH, normal or low phosphate, normal creatinine, normal magnesium, low albumin: consider hypoalbuminemia (pseudohypocalcemia)

Monitoring

• Serum calcium, phosphate, and creatinine: measure weekly during initial therapy, then monthly
• Once stabilized on therapy, measure values one to two times/year