Phosphorus and calcium work together to keep your bones and teeth strong. Healthy kidneys remove extra phosphorus, so if you have kidney failure - even with hemodialysis - your levels may be too high. Too much phosphorus can cause itching, bone pain, brittle bones, muscle aches, and heart damage, so it’s very important to make sure it doesn’t build up in your blood.

As the phosphorus builds up in the blood it will irreversibly combine with serum calcium making an insoluble product. This causes many problems. The calcium-phosphate product will float in your blood stream coating everything that it touches. It can coat and harden blood vessels and heart valves. The calcium-phosphate can also dissolve out of the blood stream forming  little rocks under the skin. This is called calcyphylaxis. The exact cause of calciphylaxis is poorly understood but has been found to involve calcifications of small and medium blood vessels leading to cutaneous skin necrosis. Lesions usually develop as a result of local skin trauma or at injection sites. The early phase involves focal central skin death, often surrounded by painful subcutaneous plaques and purpuric patches in a reticulate pattern. The late phase includes dusky plaques with induration that may progress into ulcers covered by thick, dark eschar that is very tender and leads to necrosis. Lesions may be solitary or multiple, covering several body regions.

Lesions commonly affect areas with thick adipose tissue such as the breast, thighs and abdomen. Other areas that may be involved are the legs, back and less commonly the penis. Patients with lesions that affect the lower extremities are reported to have a better prognosis. When lesions present bilaterally, they often are symmetrical and present in a "kissing" pattern. Skin lesions need to be monitored closely, because they may become infected and gangrenous. Gangrene puts patients with calciphylaxis at high risk of sepsis, which may lead to death.

Although calciphylaxis has significant skin involvement, the disease process also can involve many organs and muscle groups, including the kidneys and, less commonly, the heart, skeletal muscle, lungs and gastrointestinal tract. Skeletal muscle involvement usually is localized to the buttocks and thighs, but smaller muscle groups such as the tongue may also be involved. Painful muscle necrosis and cases of severe rhabdomyolysis have been reported.

Another problem with rising phosphorus is that when it combines with serum calcium, it effectively lowers the circulating calcium in the blood stream. On the back of your thyroid gland are four glands called the parathyroid glands.
 

These glands are responsible for maintaining a normal serum calcium by secreting a hormone called parathyroid hormone. This hormone has three functions that all will try to raise serum calcium concentration.

Mobilization of calcium from bone: Although the mechanisms remain obscure, a well-documented effect of parathyroid hormone is to stimulate osteoclasts to reabsorb bone mineral, liberating calcium into blood.

Enhancing absorption of calcium from the small intestine: Facilitating calcium absorption from the small intestine would clearly serve to elevate blood levels of calcium. Parathyroid hormone stimulates this process, but indirectly by stimulating production of the active form of vitamin D in the kidney. Vitamin D induces synthesis of a calcium-binding protein in intestinal epithelial cells that facilitates efficient absorption of calcium into blood.
Suppression of calcium loss in urine: In addition to stimulating fluxes of calcium into blood from bone and intestine, parathyroid hormone puts a brake on excretion of calcium in urine, thus conserving calcium in blood. This effect is mediated by stimulating tubular reabsorption of calcium. Another effect of parathyroid hormone on the kidney is to stimulate loss of phosphate ions in urine.

So.... High parathyroid hormone can lead to weakening of the bones.

In summary then, high serum phosphorus causes phosphorus to bind with calcium leading to calcyphylaxis and to lowering of the serum calcium level. This leads to elevation of parathyroid hormone that removes calcium from the bones.
 

Most people on hemodialysis need to take a phosphate binder to help control the level of phosphorus in their blood. Phosphate binders "soak up" extra phosphorus from food before it reaches your bloodstream. It then passes from your body in your stool. You take phosphate binders along with meals and snacks. They may cause constipation but you can ask your dietitian to suggest ways to increase fiber in your diet to help. Be sure to tell your care team if you become constipated.

Most people on hemodialysis will also need to limit the amount of phosphorus in their diet. Your dietitian will work with you to limit the following high phosphorus foods:

Dairy products of all kinds
Dried beans and peas
Whole grains
Nuts
Cola, Moxie, and pepper-type drinks (root beer, clear, and fruit-flavored sodas don’t tend to have much phosphorus)
Your care team will watch your phosphorus levels every month and help you make changes to your diet and medications if needed. If you have any questions about your phosphorus levels, ask your doctor or someone on your care team.

 

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