CMP
Low serum calcium
Normal alk phos
PTH (low or inappropriately normal in setting of hypocalcemia)
EKG
Magnesium levels
Phosphate levels (high)
Low serum calcium
Normal alk phos
Hypoparathyroidism
Vitamin D deficiency
Hypothyroidism
Pseudohypoparathyroidism 
Congenital adrenal hyperplasia
Kidney disease
Levothyroxine toxicity
Malabsorption