CORE Kidney

Bone and Kidney Disease

Chronic Kidney Disease and Mineral Bone Disorder

Kidneys play an important role in maintaining an appropriate blood level of minerals such as calcium and phosphorus. These minerals strengthen the bones. Kidneys are responsible for activating vitamin D, which is another important factor for bone health. Activated vitamin D is called calcitriol. It helps with the entry of dietary calcium from the gut into the blood.

In patients with chronic kidney disease, the kidneys cannot make sufficient amounts of calcitriol. As a result, the blood calcium level drops. On the other hand, blood phosphorus levels become elevated due to the kidneys' inability to get rid of the phosphorus as a waste product. The imbalance of calcium and phosphorus is an important feature in patients with chronic kidney disease.

There are four small glands called parathyroid glands located in the front of the neck. These glands produce a substance called parathyroid hormone (PTH). PTH can restore the blood level of calcium by drawing calcium from the bones and releasing it into the blood. Parathyroid glands produce more and more PTH in patients with chronic kidney disease as an attempt to restore the blood calcium level. The parathyroid glands will eventually become overactive and draw a lot of calcium from the bones, which results in the weakening of the bones and increased risk of bone fracture.

In addition to the bone disorder, there are other negative consequences of abnormal levels of blood minerals in patients with chronic kidney disease. The imbalance of blood levels of calcium and phosphorus may end up depositing calcium in other body tissues, such as skin or blood vessels. The deposits of calcium in the skin may cause non-healing ulcers and calcium deposits in blood vessels can damage vessel walls and lead to stroke and heart attack. The elevated blood level of phosphorus is related to an increased risk of death.

The combination of abnormal blood mineral levels and its negative consequences on bones and other organs is called Chronic Kidney Disease and Mineral Bone Disorder (CKD-MBD).  

Is CKD-MBD a rare or common condition in patients with chronic kidney disease?

CKD-MBD is common in patients with chronic kidney disease. Almost all of the kidney patients who are on dialysis are affected by CKD-MBD.

CKD-MBD can occur in patients who have reduced kidney function but not on dialysis yet. 

How can you know if you are affected by CKD-MBD?

Your doctor can periodically check your blood levels of calcium, phosphorus, PTH, and vitamin D.
 

The blood test is enough to make the diagnosis of CKD-MBD. Imaging studies may show evidence suggestive of CKD-MBD. However, performing imaging studies is not necessary routinely. Bone biopsy can be performed in some situations to examine the bone structure under the microscope directly.

How is CKD-MBD prevented and treated?

The first step is diet modification. Restriction of phosphorus rich foods is very important.

Some examples on foods with high phosphorus content:

  • Dairy products
  • Beans, peanuts
  • Dark sodas
  • Seeds (pumpkin, squash)
  • Fish

Education about the diet is critical. Your doctor may ask you to see a dietician for education about your diet.

If CKD-MBD cannot be controlled by diet changes, then your doctor may prescribe medications called phosphorus binders to limit the absorption of phosphorus from gut to blood. These medications should be taken with meals.

There are synthetic activated vitamin D which can be prescribed to reduce the abnormally elevated parathyroid hormone level in order to avoid drawing a lot of calcium from bone. On the other hand, synthetic activated vitamin D medications can increase the absorption of dietary calcium from the gut into blood.

Dialysis can remove phosphorus as well. Some patients on dialysis may require more dialysis for more phosphorus removal.

Disclaimer: The UCLA Health System cannot guarantee the accuracy of such information. The information is provided without warranty or guarantee of any kind. Please speak to your Physician before making any changes.