Researchers prefer parathyroid arteriography because it causes less discomfort to the patient and requires less experience to do the procedure. However, parathyroid arteriography provides positive results in only 50% of patients undergoing the procedure. Parathyroid venous sampling provides greater amounts of positive results but the readings are often imprecise. Parathyroid tissue secretes a hormone known as PTH (parathyroid hormone). The release of PTH is stimulated by low levels of calcium in the blood.