The diagnosis of overactive parathyroids is characterized by a combination of an elevated level of serum calcium plus an elevated level of serum parathyroid hormone.
    Diagnosis usually is made easily by documenting an increased two-site parathyroid hormone (PTH) level in a patient with elevated levels of blood and urine calcium. Only a very rare nonparathyroid malignant tumor in such patients secretes pure parathyroid hormone. Most secrete parathyroid hormone-related peptide, and this substance does not cross-react with the new parathyroid hormone assays.

Physical Examination 
• Mass in the neck. Benign tumors rarely have a mass in the neck.
• Vocal cords may be paralyzed on one side, causing hoarseness.

Blood and Other Tests 
• The normal serum calcium level is 8.5 to 10.5 mg/dl and the level in benign tumors averages 11.0 mg/dl but
  most parathyroid cancers have levels over 14 mg/dl.
• Intact or two-site PTH levels increased. 
• Urinary cyclic AMP levels are elevated in almost all patients.