Tests that examine the neck and blood are used to detect (find) and diagnose parathyroid cancer. Once blood tests are done and hyperparathyroidism is diagnosed, imaging tests may be done to help find which of the parathyroid glands is overactive. Sometimes the parathyroid glands are hard to find and imaging tests are done to find exactly where they are.   Parathyroid cancer may be hard to diagnose because the cells of a benign parathyroid adenoma and a malignant parathyroid cancer look alike. The patient's symptoms, blood levels of calcium and parathyroid hormone, and characteristics of the tumor are also used to make a diagnosis.    The following tests and procedures may be used:         -   Physical exam and history : An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patients health habits and past illnesses and treatments will also be taken.    -   Blood chemistry studies : A procedure in which a blood sample is checked to measure the amounts of certain substances released into the blood by organs and tissues in the body. An unusual (higher or lower than normal) amount of a substance can be a sign of disease. To diagnose parathyroid cancer, the sample of blood is checked for its calcium level.     -   Parathyroid hormone test: A procedure in which a blood sample is checked to measure the amount of parathyroid hormone released into the blood by the parathyroid glands. A higher than normal amount of parathyroid hormone can be a sign of disease.    -   Sestamibi scan : A type of radionuclide scan used to find an overactive parathyroid gland. A very small amount of a radioactive substance called technetium 99 is injected into a vein and travels through the bloodstream to the parathyroid gland. The radioactive substance will collect in the overactive gland and show up brightly on a special camera that detects radioactivity.    -   CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.    -   SPECT scan (single photon emission computed tomography scan): A procedure that uses a special camera linked to a computer to make a 3-dimensional (3-D) picture. A very small amount of a radioactive substance is injected into a vein. As the substance travels through the blood, the camera rotates around the neck and takes pictures. Blood flow and metabolism are higher than normal in areas where cancer cells are growing. These areas will show up brighter in the picture. This procedure may be done just before or after a CT scan.    -   Ultrasound exam: A procedure in which high-energy sound waves (ultrasound) are bounced off internal tissues or organs and make echoes. The echoes form a picture of body tissues called a sonogram.    -   Angiogram : A procedure to look at blood vessels and the flow of blood. A contrast dye is injected into the blood vessel. As the contrast dye moves through the blood vessel, x-rays are taken to see if there are any blockages.    -   Venous sampling : A procedure in which a sample of blood is taken from specific veins and checked to measure the amounts of certain substances released into the blood by nearby organs and tissues. If imaging tests do not show which parathyroid gland is overactive, blood samples may be taken from veins near each parathyroid gland to find which one is making too much PTH.