Parathyroid hormone

Think of parathyroid hormone (PTH) as the withdrawal slip for your bone bank. Each time your blood calcium levels drop, your parathyroid glands kick in. These four small, bean-shaped glands in your neck, behind your thyroid, make PTH. The job of PTH is to jump-start remodeling to take calcium out of your bones.

With failed kidneys, your blood calcium levels may drop so often that your parathyroid glands make PTH over and over. In time, the glands can grow (called hypertrophy). They can even get so big that they can't shut off.

If your PTH levels are too high, too much calcium will be withdrawn from your bones. This is called secondary hyperparathyroidism (sHPTH), and it can make your bones weak and more likely to break. The type of bone disease caused by sHPTH is called renal osteodystrophy. Target blood levels of PTH for people on dialysis are from 150 to 300 pg/mL.