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The Kidney Connection - Renal Bone Disease
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Many patients with chronic kidney disease (CKD) are unaware that the kidney is involved with the health of their bones. Renal bone disease (a.k.a renal osteodystrophy) occurs when your kidneys fail to maintain the proper levels of calcium and phosphorus in your blood. Thin and Weak Bones About 90% of those with kidney disease suffer from this condition. It causes bones to become thin and weak. They can also hurt or easily break. This occurs when calcium is lost from the bones. Renal bone disease is more serious in children because their bones are still growing. The condition slows bone growth and causes deformities and short stature. Symptoms can be seen in children with renal disease before they begin dialysis. Calcium, Phosphorus, and Calcitriol Some of the basic ways calcium and phosphorus levels are associated with renal osteodystrophy include: - Phosphorus and calcium levels in the blood are regulated by the kidneys and are dependent upon each other.
- When your kidneys are no longer functioning, the phosphorus level rises while the free calcium level decreases.
- These factors lower serum calcium, causing the body to increase the parathyroid hormone (PTH) level in the blood.
- Your kidneys help to synthesize vitamin D, the essential factor in absorbing calcium in the intestines.
- As the kidneys fail, they can no longer convert the vitamin D you consume into an "active" form the body can use. Fortunately, this form is available as a prescription medication.
- Calcium is most essential for maintaining healthy bones.
How does renal osteodystrophy progress? Calcium builds and strengthens your bones. It is found in many foods, especially dairy products. If calcium levels become too low, the four small parathyroid glands in the neck release the PTH. Too much PTH in the blood removes too much calcium from the bones. Over time, bones weaken. Found in most foods, phosphorus helps regulate calcium levels in your bones. If you have kidney failure, phosphorus levels become too high, leading to lower levels of calcium in the blood. Healthy kidneys produce a form of vitamin D called calcitriol. With renal failure, the kidneys stop producing calcitriol. When this happens, the body cannot absorb calcium from food. PTH levels also increase if calcitriol levels are too low. Bone Disorders Following are some of the types of bone disorders you should know about: - Osteoporosis. A reduction of bone mass causing porous, fragile bones.
- Osteomalacia. A reduction of calcium causing bones to soften.
- Osteitis fibrosa. Bone with calcium replaced by scar-type tissue.
- Osteosclerosis. Abnormally hardened bone.
Renal osteodystrophy can begin many years before symptoms appear or the patient needs dialysis or a kidney transplant. These symptoms are not usually seen until patients have been on dialysis for several years. More Information Last Updated April 2007
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