High Phosphorus in Cats

Published Feb. 26, 2024
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In This Article


What Is High Phosphorus in Cats?

Phosphorus is an essential mineral for your cat’s health. It plays several important roles, including growing, maintaining, and repairing cells and tissues, as well as maintaining vitamin D and calcium levels. Phosphorus is also responsible for regulating protein, fat, and carbohydrate metabolism.

Most of the phosphorus in a cat’s body is bonded to calcium, forming calcium phosphate, which creates and maintains healthy bones and teeth. The remainder of a cat’s phosphorus circulates in the blood to aid in metabolism.

When a cat’s phosphorus levels are above a normal range (2.5 mg/dL to 5.5 mg/dL), they have a condition called hyperphosphatemia. High phosphorus in cats is most often caused by kidney disease, but other conditions can also lead to hyperphosphatemia.

High phosphorus levels can result in low calcium levels, which can cause the cat’s body to break down bone to release stored calcium.

If a cat’s phosphorus level has been elevated for months or years, they may experience decreased bone density, which can cause weak bones, bone pain, and fractures. In some cases, hyperphosphatemia can cause calcium to deposit in soft tissues, especially if levels are chronically elevated. This can result in painful calcified lesions on the cat’s paw, as well as calcification in blood vessels, which can lead to cardiovascular disease.

Symptoms of High Phosphorus in Cats

Symptoms of high phosphorus in cats depend on the underlying cause of your cat’s high phosphorus levels. However, general signs include:

Causes of High Phosphorus in Cats

High phosphorus in cats occurs when a cat has too much phosphorus or too little calcium, because these minerals have an inverse relationship. Common causes of high phosphorus in cats include:

  • Chronic kidney disease (CKD)—Cats with CKD don’t eliminate enough phosphorus, and hyperphosphatemia commonly develops. High phosphorus levels are linked to disease progression and increased fatality rates in cats with CKD. Addressing hyperphosphatemia is important to prevent complications of CKD and to help your cat feel better.

  • Acute kidney injury— Conditions, such as when the bladder is blocked from an obstruction and poison ingestion, can cause acute kidney injury and can lead to high phosphorus levels because the kidneys’ ability to eliminate phosphorus is impaired.

  • Hyperthyroidism—Excess thyroid hormones lead to increased tissue breakdown that releases phosphorus into the bloodstream, causing increased phosphorus levels.

  • Bone cancer—Bone cancer can cause imbalances in phosphorus and calcium levels, leading to hyperphosphatemia.

  • Osteoporosis—When bone breakdown exceeds bone formation, phosphorus is released, contributing to hyperphosphatemia.

  • Diabetes—Diabetic cats can develop hyperphosphatemia, likely because high blood glucose levels pull phosphorus into the bloodstream.

  • Excess vitamin D ingestion—Elevated vitamin D levels cause increased absorption of phosphorus from the intestines as well as increased reabsorption by the kidneys, leading to elevated phosphorus levels.

  • Tumor lysis syndrome—Cancer treatments can cause damaged cancer cells to release phosphorus, leading to hyperphosphatemia.

Any cat can develop hyperphosphatemia. However, older cats and those who are overweight are at an increased risk for many conditions, such as CKD and diabetes, that can lead to elevated phosphorus levels.

How Veterinarians Diagnose High Phosphorus in Cats

If your cat is suspected of having hyperphosphatemia, their veterinarian will perform a comprehensive health assessment, which may include:

  • History—Your veterinarian will ask you to provide a thorough history about any symptoms your cat has been exhibiting, pre-existing health conditions, and if your cat has your cat has swallowed anything poisonous.

  • Physical exam—Your veterinarian will examine your cat from whiskers to tail to check for abnormalities.

  • Screening blood work—A complete blood count (CBC) can help assess your cat’s overall health and a biochemistry profile shows your cat’s phosphorus levels, as well as other helpful parameters such as kidney values and glucose levels.

  • Urinalysis—Your veterinarian may recommend a urinalysis to further evaluate your cat’s health.

  • Thyroid testing—If the cause of your cat’s hyperphosphatemia is not evident, your veterinarian may recommend a thyroid test.

  • X-rays—Your veterinarian may recommend X-rays to check for bone abnormalities or to assess your cat’s kidneys.

Treatment of High Phosphorus in Cats

Treatment for high phosphorus in cats depends on the underlying cause. Potential treatment strategies include:

  • CKD—CKD has no cure, but the condition can be managed to slow disease progression and improve your cat’s quality of life. Prescription diets that are low in phosphorus are beneficial for cats with CKD. If a prescription kidney diet can’t control your cat’s phosphate levels, your veterinarian may recommend medications that block phosphate absorption from the intestines.

  • Vitamin D toxicity—Treatment for cats affected by vitamin D toxicity includes intravenous (IV) fluids and medications to prevent absorption of vitamin D, and to decrease phosphorus and calcium levels.

  • Hyperthyroidism—Controlling your cat’s hyperthyroidism can help normalize their phosphorus levels.

  • Diabetes—Treating your cat’s diabetes will regulate their blood glucose concentrations, which can help normalize their phosphorus levels.

Recovery and Management of High Phosphorus in Cats

In some cases, such as if your cat has hyperthyroidism or diabetes, controlling your cat’s underlying condition will keep their phosphorus levels in normal range.

Cats with CKD require long-term monitoring and maintenance, and dietary management can take a month or two to normalize phosphorus levels. Your veterinarian will likely recheck your cat’s blood work every four to six weeks.

Prevention of High Phosphorus in Cats

Cat parents can’t prevent every case of high phosphorus. However, to reduce your feline friend’s hyperphosphatemia risk, follow these tips:

  • Keep your cat at a healthy weight to help reduce their risk for conditions, such as diabetes and CKD, that can lead to elevated phosphorus levels.

  • Store all medications and supplements in a safe location, away from your cat.

  • Schedule regular veterinary visits to monitor your cat’s health, so conditions are detected early when they are easier to treat and manage.

Jenny Alonge, DVM


Jenny Alonge, DVM


Dr. Jenny Alonge graduated from Mississippi State University College of Veterinary Medicine in 2002. She completed an equine medicine and...

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