Bone Disease

Bone disease that occurs when your kidneys fail to maintain the proper levels of calcium and phosphorus in your blood is called renal osteodystrophy. It's a common problem in people with kidney disease and affects 90 percent of dialysis patients.

Bone changes can begin many years before symptoms actually appear in people with kidney disease. Older patients and women who have gone through menopause are at greater risk for this disease because they're already vulnerable to osteoporosis, another bone disease. If left untreated, the bones gradually become thin and weak leading to bone and joint pain and increased risk of bone fractures.

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 because they help 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 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 which over time 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. This can lead to lower levels of calcium in the blood and result 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 a normal calcium balance and healthy bones. 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.

Diagnosis

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. Determining the cause of renal osteodystrophy helps the doctor decide on a course of treatment.

Treatment

Controlling PTH and phosphorus levels prevents calcium from being withdrawn from the bones. The first line of treatment is a change in diet or medication.

Reducing dietary intake of phosphorus is one of the most important steps in preventing bone disease. Almost all foods contain phosphorus, but it's especially high in milk, cheese, dried beans, peas, nuts, and peanut butter. Limit drinks such as cocoa, dark sodas, and beer. Often, medications are prescribed with meals and snacks to bind phosphorus in the bowel. These decrease the absorption of phosphorus into the blood. A dietitian can help develop a dietary plan to control phosphorus levels in the blood.

If your kidneys aren't making adequate amounts of calcitriol, you can take synthetic calcitriol as a pill or an injection. Your doctor may prescribe a calcium supplement in addition to calcitriol.

Exercise has been found to increase bone strength in some patients. It's important, however, to consult a doctor or health care professional before beginning any exercise program.

A good treatment program, including proper attention to diet and medications, can improve your body's ability to repair bones damaged by renal osteodystrophy.