📊 Definitions
• Hypocalcemia: total Ca <8.5 mg/dL (2.1 mmol/L) or ionized Ca <4.8 mg/dL (1.2 mmol/L)
• Symptoms: paresthesias, tetany, Chvostek sign, Trousseau sign, laryngospasm, seizures, prolonged QT interval
• Ionized Ca is biologically active (affected by pH, albumin)
🩺 Causes by Mechanism
• Hypoparathyroidism: DiGeorge syndrome (22q11 deletion, hypocalcemia + cardiac defects), autoimmune, postsurgical, genetic (CASR, GCMB)
• Vitamin D deficiency/rickets: nutritional (breastfed without supplements), malabsorption (CF, celiac), liver disease, anticonvulsants
• Pseudohypoparathyroidism: peripheral resistance to PTH (Albright hereditary osteodystrophy), normal/elevated PTH, hypocalcemia, hyperphosphatemia
• Renal failure: decreased 1,25-OH vitamin D, hyperphosphatemia
• Other: pancreatitis (saponification), hungry bone syndrome (post-parathyroidectomy), Mg deficiency (impaired PTH secretion/action), tumor lysis (hyperphosphatemia)
📋 Evaluation
• Total Ca, ionized Ca, PTH, vitamin D (25-OH, 1,25-OH), phosphate, Mg, albumin, renal function
• EKG: prolonged QT interval
• Genetic testing for DiGeorge (FISH 22q11), CASR mutations
⚠️ Emergency Treatment
• Acute symptomatic tetany/seizures: IV calcium gluconate (10%) 100-200 mg/kg (1-2 mL/kg) over 15-30 minutes, then continuous infusion
• Chronic: oral calcium (calcium carbonate or citrate), vitamin D (calcitriol for hypoparathyroidism)
📌 Decision strategy: Correct hypocalcemia with IV calcium if symptomatic. Check PTH, Mg, vitamin D, phosphate. DiGeorge syndrome presents with hypocalcemia + cardiac defects + T-cell deficiency.