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Hormones and Minerals
In healthy adults, bone tissue is continually being remodeled and rebuilt. The kidneys play an important role in maintaining healthy bone mass and structure because one of their jobs is to balance calcium and phosphorus levels in the blood.
Calcium is a mineral that builds and strengthens bones. It's found in many foods, particularly milk and other dairy products. If calcium levels in the blood become too low, four small glands in the neck called the parathyroid glands release a hormone called parathyroid hormone (PTH). This hormone draws calcium from the bones to raise blood calcium levels. Too much PTH in the blood will remove too much calcium from the bones; over time, the constant removal of calcium weakens the bones.
Phosphorus, which is found in most foods, also helps regulate calcium levels in the bones. Healthy kidneys remove excess phosphorus from the blood. When the kidneys stop working normally, phosphorus levels in the blood can become too high, leading to lower levels of calcium in the blood and resulting in the loss of calcium from the bones.
Healthy kidneys produce calcitriol, a form of vitamin D, to help the body absorb dietary calcium into the blood and the bones. If calcitriol levels drop too low, PTH levels increase, and calcium is removed from the bones. Calcitriol and PTH work together to keep calcium balance normal and bones healthy. In a patient with kidney failure, the kidneys stop making calcitriol. The body then can't absorb calcium from food and starts removing it from the bones.
How is renal osteodystrophy diagnosed?
To diagnose renal osteodystrophy, your doctor may take a sample of your blood to measure levels of calcium, phosphorus, PTH, and calcitriol. The doctor may perform a bone biopsy to see how dense your bones are. A bone biopsy is done under local anesthesia and involves removing a small sample of bone from the hip and analyzing it under a microscope. Determining the cause of renal osteodystrophy helps the doctor decide on a course of treatment.