What is renal bone disease?
Chronic kidney disease (CKD) associated mineral bone disease (MBD) happens when there are flaws in calcium, phosphorus, parathyroid hormone, and vitamin D metabolism. This leads to unusual bone turnover, mineralization, and promotes calcification of blood vessels and soft-tissue.1 When blood vessels become calcified, they become hard and can put you at risk for stroke and heart attacks.
How does CKD cause problems with bone?
CKD-MBD is a common complication seen in many patients with CKD, and almost all patients on dialysis.2 This usually starts in CKD stage 3, however the severity varies from patient to patient. There are several factors that play a role in developing CKD-MBD.
Phosphorous is present in many foods. Working kidneys usually remove extra levels of phosphorous in the body. In patients with CKD, the kidneys are not able to remove unneeded phosphorous. High levels of phosphorous lead to increased levels of parathyroid hormone.2 The parathyroid glands are four small glands in the neck that release the parathyroid hormone. Parathyroid hormone works to start-up the removing of phosphorous through the kidneys as well as increase calcium levels in the body. These collective duties of parathyroid hormone result in the breakdown of bone since most of the calcium in the body is stored in bone. Over time, this will weaken your bones and put you at risk of brittle and broken bones.
Another factor in bone disease is vitamin D. Vitamin D helps with calcium balance in the body. We get vitamin D mainly through diet and sunlight. Healthy kidneys change vitamin D to a usable form for the body called calcitriol. Calcitriol increases calcium intake in the stomach from our diet. Non-working kidneys lead to low levels of calcitriol which leads to further increase in parathyroid hormone. This makes hyper-parathyroid hormone levels even higher.
How is bone mineral disease in CKD diagnosed?
Bone changes can begin long before any symptoms appear. The rising of blood work can include levels of calcium, phosphorous, parathyroid hormone, and vitamin D. There are no medical image tests to diagnose CKD-MBD. However, a stomach x-ray can be done to test for stomach calcifications that may occur. If diagnosis is uncertain, a bone biopsy may be needed. The biopsies of patients with bone disease may reflect high or low bone turnover. This is usually performed under local anesthesia and a portion of the hip bone is taken as a sample. There are four different types of bones seen in patients suffering from renal bone disease. How the bone looks depends on the amount of bone turnover that is occurring. In patients that are not on dialysis, high bone turnover bone disease is more common, whereas patients that are on dialysis low bone turnover is more prevalent. 3
How is bone mineral disease in CKD treated? (Table 1)
The usual way of treatment is to control phosphorous and parathyroid hormone levels. This can be achieved through changes in your diet, dialysis, or medication. You will need to reduce your dietary intake of phosphorus by avoiding milk, seeds, cheese, nuts, peanut butter, dark soda, and beer. Medications called phosphate binders can be taken with meals and snacks to combine the phosphorus in the stomach and lower phosphorus intake in the blood. Examples of phosphate binders are calcium carbonate (tums), calcium acetate (PhosLo), sevelamer hydrochloride (Renagel). Vitamin D can also be added, however caution is needed as this can increase calcium levels in the blood, which can contribute to more calcification. If all these treatments don’t work and the parathyroid hormone level continues to remain high, your doctor may consider removing the parathyroid gland. Exercise will help make bones stronger.
|Avoid foods high in phosphorous||Decreases the amount of phosphorous the kidney has to excrete|
|Phosphate Binders||Binds phosphorous in the gut, therefore decreasing amount of phosphorous in the blood|
|Parathyroid gland removal||Controls level of parathyroid hormone (if does not respond to medical treatment).|
|Exercise||Increases bone strength|
Why is this so important?
Bone disease affects a lot of people with CKD. If left untreated, you could be at risk of joint pains and broken bones. Also, the metabolic abnormalities that occur in CKD-MBD can put you at risk for cardiovascular complications like stroke and heart attack.
1. Uhlig, Katrin, Jeffrey S. Berns, Bryan Kestenbaum, Raj Kumar, Mary B. Leonard, Kevin J. Martin, Stuart M. Sprague, and Stanley Goldfarb. “KDOQI US Commentary on the 2009 KDIGO Clinical Practice Guideline for the Diagnosis, Evaluation, and Treatment of CKD– Mineral and Bone Disorder (CKD-MBD).” American Journal of Kidney Diseases 55.5 (2010): 773-99.
2. Mitch, William. “132.” Goldman: Goldman’s Cecil Medicine. 24th ed. New York: Elsevier, 2012. 812-13.
3. Thomas, R., A. Kanso, and J. Sedor. “Chronic Kidney Disease and Its Complications.” Primary Care: Clinics in Office Practice 35.2 (2008): 329-44.
This article was originally printed in the March 2013 issue of aakpRENALIFE magazine.