Hypocalcemia

Initial confirmation

• Hypocalcemia → Confirm with repeat measurement +/- ionized Ca++
• Then assess: Serum Mg++, Intact PTH level, and vitamin D status

Serum Mg++ — Low

• Evaluate for etiologies of hypomagnesemia:
• 1. Gastrointestinal losses (vomiting, diarrhea, malabsorption)
• 2. Renal wasting
• 3. Alcoholism
• 4. Malnutrition
• 5. Drug-induced
• 6. Perform 24 hr urine and further testing as appropriate

Serum Mg++ — Normal

• → Proceed to evaluate for hypoparathyroidism

Intact PTH level — Elevated

• Evaluate for etiologies of secondary hyperparathyroidism:
• 1. Malabsorption
• 2. Vitamin D deficiency
• 3. Pseudohypoparathyroidism types 1, 2
• 4. Vitamin D-dependent rickets types 1, 2

Intact PTH level — Low/inappropriately normal

• → Evaluate for hypoparathyroidism

Evaluate for hypoparathyroidism

• 1. Complete medical history, family history, past surgical history for prior parathyroid, thyroid, or neck surgery
• 2. Physical examination (neck scar, candidiasis, signs of tetany, cataracts, short stature, mental retardation)
• 3. Family history: mental retardation, features of autoimmune disorders (Addison disease, autoimmune thyroid disease), deafness, renal anomalies, thalassemia, or iron overload
• 4. Further lab testing, genetic screening, and testing of family members as appropriate (activating CaSR mutation; PTH mutation; AIRE, GCMB, or GATA3 mutational analysis)
• 5. Assessment of autoantibodies (21-hydroxylase abs, antiparathyroid abs)
• 6. Hearing test, renal imaging (as appropriate)

Vitamin D status (25-hydroxy vitamin D measurement)

• Vitamin D sufficiency confirmed (25-hydroxy vitamin D >20 ng/mL) → Evaluate for hypoparathyroidism
• Vitamin D deficiency confirmed → Evaluate for gastrointestinal losses, low dietary intake, low sunlight exposure → Replete vitamin D