Bone Disease in Chronic Kidney Disease

CKD-MBD occurs when the kidneys fail to maintain the proper levels of calcium and phosphorus in the blood, leading to abnormal bone hormone levels. CKD-MBD is a common problem in people with kidney disease and affects almost all patients receiving dialysis.
CKD-MBD is most serious in children because their bones are still growing. The condition slows bone growth and causes deformities. One such deformity occurs when the legs bend inward toward each other or outward away from each other; this deformity is referred to as “renal rickets.” Another serious complication is short stature. Symptoms can be seen in growing children with renal disease even before they start dialysis.
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 and ensure the vitamin D a person receives from sunlight and food becomes activated.
Calcium is a mineral that builds and strengthens bones. Calcium is 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, an element 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 higher PTH levels and the loss of calcium from the bones. Even before blood levels of phosphorus become elevated, the kidneys are forced to work harder to clear phosphorus from the body.
How is CKD-MBD treated?
CKD-MBD can be treated with changes in diet. Reducing dietary intake of phosphorus is one of the most important steps in preventing bone disease. Almost all foods contain phosphorus, but it is especially high in milk, cheese, dried beans, peas, nuts, and peanut butter. Drinks such as cocoa, dark sodas, and beer are also high in phosphorus. Often, medications called phosphate binders—such as calcium carbonate (Tums), calcium acetate (PhosLo), sevelamer hydrochloride (Renagel), or lanthanum carbonate (Fosrenol)—are prescribed with meals and snacks to bind phosphorus in the bowel. These medications decrease the absorption of phosphorus into the blood. A renal dietitian can help develop a dietary plan to control phosphorus levels in the blood.