PTH is a hormone your parathyroid glands make, which helps control the calcium level in your blood. If calcium blood levels are too low, your parathyroid glands will release PTH to raise calcium levels. If calcium levels are too high, these glands will stop making PTH. This test helps diagnose hyperparathyroidism (too much PTH) and hypoparathyroidism (too little PTH), monitor kidney disease, and determine whether high calcium blood levels relate to parathyroid glands.