Phosphate promotes the progression of chronic kidney disease (CKD)
The vicious cycle of hyperphosphataemia
- In cats with CKD, phosphate is retained in the metabolic process. The resulting hyperphosphataemia is one of the main causes of disease progression. Reducing phosphate can prolong the life of the chronic kidney diseased cat.
Loss of nephrons leads to impaired renal function as a result of which less phosphate is eliminated.
Consequently, more phosphate remains in the blood, resulting in hyperphosphataemia.
At the same, various mechanisms reduce the blood calcium level, causing hypocalcaemia. Calcium and phosphate are evenly balanced. Different processes and hormones contribute to maintaining that balance.
4. When the blood calcium level is too low (hypocalcaemia), parathyroid hormone (PTH) is released from the adrenal cortex. PTH is produced for the purpose of raising the blood calcium level and reducing the blood phosphate level. At the same time, PTH increases the elimination of more phosphate. Elimination of phosphate is, however, greatly reduced in an impaired kidney so that phosphate builds up in the blood causing an increase in the existing hyperphosphataemia.
5. PTH releases calcium from the bones in order to raise the blood calcium level. Calcium release from bone is achieved by bone depletion. As calcium is stored in bone as calcium phosphate, phosphate is also automatically released so that the already existing hyperphosphataemia is further increased.
Release of calcium from the bones can lead to their softening and becoming deformed and also raises not only the level of phosphate but also of blood calcium.
6. Combined with an elevated phosphate level (hyperphosphataemia), a normal, but especially an elevated calcium level (hypercalcaemia) can lead to calcification of soft tissue, blood vessels, the stomach wall, paws and, above all, the kidneys.
Calcification of the kidneys leads to further kidney damage and accelerates the progression of chronic kidney disease.
It is therefore clear why hyperphosphataemia results in further kidney damage and a poorer CKD prognosis.
7. The kidneys play a role in regulating the calcium and phosphate levels in the blood by transforming vitamin D into its active form, calcitriol. Calcitriol is an adversary of parathyroid hormone. It inhibits the release of PTH.
If kidney damage in CKD causes less calcitriol to be produced, PTH inhibition will be insufficient, resulting in further depletion of the bones, further elevation of the blood calcium and phosphate levels, increased calcification and thus kidney damage. A vicious cycle results from the uninhibited effects of the parathyroid hormone.
This state of excessive PTH production caused by CKD is known as secondary hyperparathyroidism and has a negative impact on cats’ kidneys (kidney calcification = nephrocalcinosis) and the entire organism.
8. This explains why phosphate reduction is important for cats with CKD.
Reducing phosphate with the aid of the only phosphate binder approved for animals, lanthanum carbonate, can help to extend the life of your cat.
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