PTH and Hypocalcemia: An initial workup of her hypocalcemia (with the patient on supplementation) was consistent with primary hypoparathyroidism: an ionized calcium of 4.3 mg/dL (1.07 mmol/L) (normal reference range: 4.5-5.6 mg/dL; 1.13-1.40 mmol/L), serum calcium 8.5 mg/dL (2.13 mmol/L) (normal reference range: 8.7-10.3 mg/dL; 2.17-2.58 mmol/L), serum phosphorous 4.6 mg/dL (1.49 mmol/L) (normal reference range: 3.0-4.3 mg/dL; 0.97-1.39 mmol/L), and an inappropriately low PTH of 12 pg/mL (1.27 pmol/L) (normal reference range: 15-65 pg/mL; 1.59-7.09 pmol/L).