hypocalcemia
HYPOCALCEMIA
Hypocalcemia is the occurs when serum calcium concentration is below the lower limit of normal range.
Acute hypocalcemia has neuromuscular tetany as hallmark symptom. Patients have rapid decrease in serum calcium and present with symptomatic hypocalcemia.
It is an emergency condition and requires immediate attention. Ca (IV) should be administered until signs and symptoms abate or until serum Ca levels rise.
Chronic hypocalcemia has asymptomatic mild hypocalcemia. Treatment is necessary to avoid long term complications. Oral Ca may be administered.

Classification

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)
Chronic Hypocalcemia
  • Asymptomatic mild hypocalcemia

Laboratory Tests

  • 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
Parathyroid-Related Disorders
  • 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 Related Disorders
  • 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
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