Hypocalcemia Diagnosis

Acute Hypocalcemia

• Patients have rapid decrease in serum Ca and present with symptomatic hypocalcemia
• Hallmark is neuromuscular tetany
• Serum Ca <1.875 mmol/L (7.5 mg/dL)

• Asymptomatic mild hypocalcemia

• Serum Ca (ionized Ca is preferred measurement)
  • Should be corrected to an albumin level of 40 mmol/L

• Albumin
  • Hypoalbuminemia may result in false hypocalcemia if total serum Ca is measured
  • For each 1 g/dL decrease in albumin below 4 g/dL, subtract 0.8 mg/dL from the total serum Ca

• Phosphorous, PTH, Mg and if available, 25(OH)D, 1,25(OH)₂D

• Serum Ca is low, serum phosphate is high, 1,25(OH)₂D is low, PTH levels are usually low or undetectable
  • PTH levels may be inappropriately normal if some PTH production is preserved
  • PTH levels will be high if hypocalcemia is caused by resistance to PTH

• Vit D deficient patient will have hypophosphatemia, high PTH, low level of 1,25(OH)₂D
  • 1,25(OH)₂D can be low but stimulation of the renal 1-α-hydroxylase by PTH can result in normal or elevated 1,25(OH)₂D

• Increased metabolism of Vit D can lead to low levels of 25(OH)D which may occur in patients given anticonvulsant or anti TB medications eg Phenobarbital, Phenytoin, Rifampicin