Hyperphosphatemia in Dogs (High Phosphorus Levels)

What is Hyperphosphatemia in Dogs?

Hyperphosphatemia is the term for high phosphorus levels in the blood. Phosphorus is a mineral found in bones that, together with calcium, helps to build strong, healthy bone structure. Phosphorus also helps to maintain cell structures and aids in cell energy production. Most of the phosphorus in a dog’s body is stored in bone, but a small percentage is present in the blood.  

Calcium and phosphorus have an inverse relationship. When phosphorus levels in the blood are high, calcium levels tend to be lower. For this reason, clinical signs of high phosphorus correlate with clinical signs of too little calcium in the blood (hypocalcemia). 

Phosphorus is absorbed in the small intestine and is released in the urine. The kidneys and parathyroid glands are important in maintaining phosphorus levels. Diseases associated with the kidneys, bones, parathyroid gland, or gastrointestinal tract can lead to hyperphosphatemia. The most common disease leading to hyperphosphatemia is chronic renal failure (CRF). 

Symptoms of Excess Phosphorus Levels in the Blood of Dogs

Signs of kidney disease can be seen in cases of chronic, or long-lasting, hyperphosphatemia. These symptoms include increased thirst and urination, diluted urine, dehydration, or inappropriate urination. In animal that already have been diagnosed with chronic renal failure, hyperphosphatemia can speed up the progression of this disease. 

In high levels, phosphate can combine with calcium to create a solid. This causes a syndrome called metastatic mineralization, which means the decomposition of chemical compounds in otherwise normal tissues. The most common body systems affected by metastatic mineralization are the urinary system (the kidneys in particular) and the gastrointestinal system. Symptoms of metastatic mineralization can include muscle tremors, muscle atrophy, or seizures. 

Hyperphosphatemia in dogs can also cause lethargy, depression, or loss of appetite. 

Causes of Excess Phosphorus Levels in the Blood of Dogs

Young, growing dogs can have higher phosphorus levels due to increased growth hormone in their systems and increased need for phosphorus for bone development. Older dogs are more likely to have diseases that will eventually lead to the development of chronic hyperphosphatemia. 

Kidney disease is the most common cause of hyperphosphatemia in dogs. However, it can also be related to increased absorption of phosphorus through the gastrointestinal tract or through transcellular shifting (transport of solutes by a cell through a cell) of phosphorus, usually from bone. 

Hyperphosphatemia can also be related to: 

• Vitamin D toxicity  

• Enema intoxication through the use of phosphate-containing enemas  

• Urinary tract obstruction 

• Endocrinopathies (hyperthyroidism, hypoparathyroidism, hypoadrenocorticism) 

• Cancer  

• Nutritional supplementation  

• Bladder rupture  

• Bone or muscle disease  

• Xylitol intoxication 

• Snakebites 

• Acromegaly (overproduction of growth hormone) 

Occasionally, phosphorus will be elevated in cases of serious trauma or in conditions such as acute tumor lysis syndrome (seen most commonly with end stage tumors) and rhabdomyolysis, which is a muscular disorder. 

How Veterinarians Diagnose Hyperphosphatemia in Dogs

Hyperphosphatemia is diagnosed through a blood work profile called a biochemistry panel. Other diagnostic methods may be needed to discover the underlying cause of hyperphosphatemia. Those include imaging or additional bloodwork (such as thyroid testing or a complete blood count).

Treatment for Hyperphosphatemia in Dogs

Hospitalization may be needed in severe cases of hyperphosphatemia. Your dog may receive IV fluid therapy and medications such as dextrose, insulin, aluminum hydroxide, or calcium carbonate that can help to decrease phosphorus in the blood. 

When dogs are diagnosed with chronic elevations of blood phosphorus, they are commonly treated orally with phosphate binders. Dietary restriction of phosphorus is recommended through switching your dog to a low protein or prescription renal care diets. Because phosphorus and calcium bind together, in some cases restricting calcium intake is also recommended. 

In all cases of hyperphosphatemia, the underlying cause must be found and correctly treated to have the best outcome for your dog. 

Recovery and Management of Hyperphosphatemia in Dogs

Bloodwork is recommended at regular intervals in patients that have experienced frequent episodes of hyperphosphatemia or have a disease that causes hyperphosphatemia. Once diagnosed, it can be possible for the condition to be managed at home with medications including oral phosphate binders or phosphate-restricted diets. 

Dogs with acute cases of hyperphosphatemia that occur because of issues like vitamin D toxicity should recover fully after treatment with IV fluid therapy and use of medications for binding the phosphorus and are unlikely to require lifelong, at home management.