In patients with parathyroid carcinoma, mean serum calcium declined from 14.1 mg/ dl to 12.4 mg/ dl (3.5 mmol/ l to 3.1 mmol/ l), while in patients with primary HPT, serum calcium levels declined from 12.7 mg/ dl to 10.4 mg/ dl (3.2 mmol/ l to 2.6 mmol/ l).