The purpose of the parathyroid hormone (PTH) test is to measure the PTH or parathormone levels in the blood. Any abnormalities in PTH can be detected using the PTH blood test. The test is compatible for both adults and children, irrespective of gender. Your doctor will prescribe a PTH blood test if calcium or phosphorus abnormalities are suspected. Symptoms like increased thirst, nausea, vomiting, fatigue and abdominal pain might indicate this.