Bone Disease in CKD

Having healthy bones is essential for maintaining the body structure and mobility. The human skeleton supports the body’s weight and protects the brain and other organs. The skeleton is also the storehouse for two important minerals — calcium and phosphorus.

In people with bone disease related to kidney failure, bone cells called osteoclasts and osteoblasts are often not in balance. This condition is called renal osteodystrophy, also known as Chronic Kidney Disease – Mineral Bone Disease (CKD-MBD). The bone cells get out of balance when calcium, parathyroid hormone (PTH), phosphorus and activated vitamin D are all out of balance.

Over time, renal osteodystrophy can cause the bones to break easily and harden the soft tissues of the body, including the heart. This may even lead to a higher death rate in people with end stage renal disease (ESRD).

Healthy kidneys activate vitamin D into a form that helps the body to absorb calcium from the bowel. If the activated vitamin D levels drop too low, less calcium is absorbed from the diet, and blood calcium levels fall. The kidney also removes phosphate from the body, so in cases of renal failure the phosphate tends to accumulate and its levels rise in the blood. This means that in renal failure patients, calcium tends to be low and phosphate high. This causes four small glands in the neck – the parathyroid glands – to release a hormone known as the parathyroid hormone (PTH). PTH draws calcium from the bones to raise blood calcium levels, resulting in weakened bones.

Diagnosis and Treatment

CKD-MBD can be suspected in the following conditions:

  • the blood calcium level is low
  • the blood phosphate level is high
  • the blood parathyroid hormone (PTH) is high

Reducing dietary intake of phosphate is most important for preventing CKD-MBD. Also, tablets called phosphate binders – such as calcium carbonate, calcium acetate, aluminium hydroxide, lanthanum or sevelamer – are often prescribed. It is essential that these tablets are taken with meals (and snacks) to bind the phosphate in the bowel. Phosphate is then removed in the stools. If this does not work, a person can be prescribed a synthetic form of Vitamin D such as alfacalcidol, calcitriol or paricalcitol. Newer drugs available now include cinacalcet. Being on dialysis will also help to correct the problem, as it removes phosphate from, and puts calcium into, the blood. If this is not enough, increasing the amount of dialysis a patient receives can improve CKD-MBD control.